Why doesn t Java offer operator overloading

Question

Coming from C   to Java  the obvious unanswered question is why didn t Java include operator overloading   Isn t Complex a  b  c  a   b   c  much simpler than Complex a  b  c  a   b add c     Is there a known reason for this  valid arguments for not allowing operator overloading  Is the reason arbitrary  or lost to time

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Technically  there is operator overloading in every programming language that can deal with different types of numbers  e g  integer and real numbers  Explanation  The term overloading means that there are simply several implementations for one function  In most programming languages different implementations are provided for the operator    one for integers  one for reals  this is called operator overloading   Now  many people find it strange that Java has operator overloading for the operator   for adding strings together  and from a mathematical standpoint this would be strange indeed  but seen from a programming language s developer s standpoint  there is nothing wrong with adding builtin operator overloading for the operator   for other classes e g  String  However  most people agree that once you add builtin overloading for   for String  then it is generally a good idea to provide this functionality for the developer as well   A completely disagree with the fallacy that operator overloading obfuscates code  as this is left for the developer to decide  This is na  ve to think  and to be quite honest  it is getting old    1 for adding operator overloading in Java 8

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I think that people making decisions simply forgot about complex values   matrix algebra  set theory and other cases when overloading would allow to use the standard notation without building everything into the language  Anyway  only mathematically oriented software really benefits from such features  A generic customer application almost never needs them  They arguments about the unnecessary obfuscation are obviously valid when a programmer defines some program-specific operator where it could be the function instead  A name of the function  when clearly visible  provides the hint that it does  Operator is a function without the readable name  Java is generally designed about philosophy that some extra verbosity is not bad as it makes the code more readable  Constructs that do the same just have less code to type in used to be called a  quot syntax sugar quot  in the past  This is very different from the Python philosophy  for instance  where shorter is near always seen as better  even if providing less context for the second reader

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Well you can really shoot yourself in the foot with operator overloading  It s like with pointers people make stupid mistakes with them and so it was decided to take the scissors away   At least I think that s the reason  I m on your side anyway

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Assuming you wanted to overwrite the previous value of the object referred to by a  then a member function would have to be invoked   Complex a  b  c         a   b add c     In C    this expression tells the compiler to create three  3  objects on the stack  perform addition  and copy the resultant value from the temporary object into the existing object a   However  in Java  operator  doesn t perform value copy for reference types  and users can only create new reference types  not value types  So for a user-defined type named Complex  assignment means to copy a reference to an existing value   Consider instead   b set 1  0      initialize to real number  1  a   b   b set 2  0   assert   a equals b        this assertion will fail   In C    this copies the value  so the comparison will result not-equal  In Java  operator  performs reference copy  so a and b are now referring to the same value  As a result  the comparison will produce  equal   since the object will compare equal to itself   The difference between copies and references only adds to the confusion of operator overloading  As  Sebastian mentioned  Java and C  both have to deal with value and reference equality separately -- operator  would likely deal with values and objects  but operator  is already implemented to deal with references   In C    you should only be dealing with one kind of comparison at a time  so it can be less confusing  For example  on Complex  operator  and operator   are both working on values -- copying values and comparing values respectively

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This is not a good reason to disallow it but a practical one   People do not always use it responsibly  Look at this example from the Python library scapy    gt  gt  gt  IP    lt IP   gt   gt  gt  gt  IP   TCP    lt IP frag 0 proto TCP   lt TCP   gt  gt   gt  gt  gt  Ether   IP   TCP    lt Ether type 0x800   lt IP frag 0 proto TCP   lt TCP   gt  gt  gt   gt  gt  gt  IP   TCP    GET   HTTP 1 0 r n r n   lt IP frag 0 proto TCP   lt TCP   lt Raw load  GET   HTTP 1 0 r n r n    gt  gt  gt   gt  gt  gt  Ether   IP   IP   UDP    lt Ether type 0x800   lt IP frag 0 proto IP   lt IP frag 0 proto UDP   lt UDP   gt  gt  gt  gt   gt  gt  gt  IP proto 55  TCP    lt IP frag 0 proto 55   lt TCP   gt  gt    Here is the explanation      The   operator has been used as a composition operator between two   layers  When doing so  the lower layer can have one or more of its   defaults fields overloaded according to the upper layer   You still   can give the value you want   A string can be used as a raw layer

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Saying  that operator overloading leads to logical errors of type that operator does not match the operation logic  it s like saying nothing  The same type of error will occur if function name is inappropriate for operation logic - so what s the solution  drop the ability of function usage     This is a comical answer -  Inappropriate for operation logic   every parameter name  every class  function or whatever can be logicly inappropriate  I think that this option should be available in respectable programing language  and those that think that it s unsafe - hey no bothy says you have to use it   Lets take the C   They drooped the pointers but hey - there is  unsafe code  statement - program as you like on your own risk

User · Answer

Technically  there is operator overloading in every programming language that can deal with different types of numbers  e g  integer and real numbers  Explanation  The term overloading means that there are simply several implementations for one function  In most programming languages different implementations are provided for the operator    one for integers  one for reals  this is called operator overloading   Now  many people find it strange that Java has operator overloading for the operator   for adding strings together  and from a mathematical standpoint this would be strange indeed  but seen from a programming language s developer s standpoint  there is nothing wrong with adding builtin operator overloading for the operator   for other classes e g  String  However  most people agree that once you add builtin overloading for   for String  then it is generally a good idea to provide this functionality for the developer as well   A completely disagree with the fallacy that operator overloading obfuscates code  as this is left for the developer to decide  This is na  ve to think  and to be quite honest  it is getting old    1 for adding operator overloading in Java 8

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Assuming you wanted to overwrite the previous value of the object referred to by a  then a member function would have to be invoked   Complex a  b  c         a   b add c     In C    this expression tells the compiler to create three  3  objects on the stack  perform addition  and copy the resultant value from the temporary object into the existing object a   However  in Java  operator  doesn t perform value copy for reference types  and users can only create new reference types  not value types  So for a user-defined type named Complex  assignment means to copy a reference to an existing value   Consider instead   b set 1  0      initialize to real number  1  a   b   b set 2  0   assert   a equals b        this assertion will fail   In C    this copies the value  so the comparison will result not-equal  In Java  operator  performs reference copy  so a and b are now referring to the same value  As a result  the comparison will produce  equal   since the object will compare equal to itself   The difference between copies and references only adds to the confusion of operator overloading  As  Sebastian mentioned  Java and C  both have to deal with value and reference equality separately -- operator  would likely deal with values and objects  but operator  is already implemented to deal with references   In C    you should only be dealing with one kind of comparison at a time  so it can be less confusing  For example  on Complex  operator  and operator   are both working on values -- copying values and comparing values respectively

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James Gosling likened designing Java to the following       There s this principle about moving  when you move from one apartment to another apartment  An interesting experiment is to pack up your apartment and put everything in boxes  then move into the next apartment and not unpack anything until you need it  So you re making your first meal  and you re pulling something out of a box  Then after a month or so you ve used that to pretty much figure out what things in your life you actually need  and then you take the rest of the stuff -- forget how much you like it or how cool it is -- and you just throw it away  It s amazing how that simplifies your life  and you can use that principle in all kinds of design issues  not do things just because they re cool or just because they re interesting     You can read the context of the quote here  Basically operator overloading is great for a class that models some kind of point  currency or complex number  But after that you start running out of examples fast   Another factor was the abuse of the feature in C   by developers overloading operators like   amp  amp          the cast operators and of course  new   The complexity resulting from combining this with pass by value and exceptions is well covered in the Exceptional C   book

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Assuming Java as the implementation language then a  b  and c would all be references to type Complex with initial values of null  Also assuming that Complex is immutable as the mentioned BigInteger and similar immutable BigDecimal  I d I think you mean the following  as you re assigning the reference to the Complex returned from adding b and c  and not comparing this reference to a      Isn t    Complex a  b  c  a   b   c        much simpler than   Complex a  b  c  a   b add c

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Groovy has operator overloading  and runs in the JVM  If you don t mind the performance hit  which gets smaller everyday   It s automatic based on method names  e g       calls the  plus argument   method

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Assuming you wanted to overwrite the previous value of the object referred to by a  then a member function would have to be invoked   Complex a  b  c         a   b add c     In C    this expression tells the compiler to create three  3  objects on the stack  perform addition  and copy the resultant value from the temporary object into the existing object a   However  in Java  operator  doesn t perform value copy for reference types  and users can only create new reference types  not value types  So for a user-defined type named Complex  assignment means to copy a reference to an existing value   Consider instead   b set 1  0      initialize to real number  1  a   b   b set 2  0   assert   a equals b        this assertion will fail   In C    this copies the value  so the comparison will result not-equal  In Java  operator  performs reference copy  so a and b are now referring to the same value  As a result  the comparison will produce  equal   since the object will compare equal to itself   The difference between copies and references only adds to the confusion of operator overloading  As  Sebastian mentioned  Java and C  both have to deal with value and reference equality separately -- operator  would likely deal with values and objects  but operator  is already implemented to deal with references   In C    you should only be dealing with one kind of comparison at a time  so it can be less confusing  For example  on Complex  operator  and operator   are both working on values -- copying values and comparing values respectively

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The Java designers decided that operator overloading was more trouble than it was worth  Simple as that   In a language where every object variable is actually a reference  operator overloading gets the additional hazard of being quite illogical - to a C   programmer at least  Compare the situation with C  s    operator overloading and Object Equals and Object ReferenceEquals  or whatever it s called

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There are a lot of posts complaining about operator overloading  I felt I had to clarify the  quot operator overloading quot  concepts  offering an alternative viewpoint on this concept   Code obfuscating  This argument is a fallacy    Obfuscating is possible in all languages    It is as easy to obfuscate code in C or Java through functions methods as it is in C   through operator overloads     C   T operator    const T  amp  a  const T  amp  b     add        T c      c value   a value - b value      subtract        return c         Java static T add  T a  T b     add        T c   new T        c value   a value - b value      subtract        return c         C    T add  T a  T b     add           T c      c value   a value - b value      subtract           return c           Even in Java s standard interfaces For another example  let s see the Cloneable interface in Java  You are supposed to clone the object implementing this interface  But you could lie  And create a different object  In fact  this interface is so weak you could return another type of object altogether  just for the fun of it  class MySincereHandShake implements Cloneable       public Object clone                return new MyVengefulKickInYourHead              As the Cloneable interface can be abused obfuscated  should it be banned on the same grounds C   operator overloading is supposed to be  We could overload the toString   method of a MyComplexNumber class to have it return the stringified hour of the day  Should the toString   overloading be banned  too  We could sabotage MyComplexNumber equals to have it return a random value  modify the operands    etc  etc  etc   In Java  as in C    or whatever language  the programmer must respect a minimum of semantics when writing code  This means implementing a add function that adds  and Cloneable implementation method that clones  and a    operator than increments   What s obfuscating anyway  Now that we know that code can be sabotaged even through the pristine Java methods  we can ask ourselves about the real use of operator overloading in C      Clear and natural notation  methods vs  operator overloading  We ll compare below  for different cases  the  quot same quot  code in Java and C    to have an idea of which kind of coding style is clearer     Natural comparisons     C   comparison for built-ins and user-defined types bool    isEqual            A    B   bool    isNotEqual         A    B   bool    isLesser           A  lt   B   bool    isLesserOrEqual    A  lt   B       Java comparison for user-defined types boolean isEqual            A equals B    boolean isNotEqual           A equals B    boolean isLesser           A comparesTo B   lt  0   boolean isLesserOrEqual    A comparesTo B   lt   0    Please note that A and B could be of any type in C    as long as the operator overloads are provided  In Java  when A and B are not primitives  the code can become very confusing  even for primitive-like objects  BigInteger  etc         Natural array container accessors and subscripting     C   container accessors  more natural value          myArray 25               subscript operator value          myVector 25              subscript operator value          myString 25              subscript operator value          myMap  quot 25 quot                subscript operator myArray 25     value                    subscript operator myVector 25    value                    subscript operator myString 25    value                    subscript operator myMap  quot 25 quot      value                    subscript operator     Java container accessors  each one has its special notation value          myArray 25               subscript operator value          myVector get 25          method get value          myString charAt 25       method charAt value          myMap get  quot 25 quot            method get myArray 25     value                    subscript operator myVector set 25  value                  method set myMap put  quot 25 quot   value                   method put  In Java  we see that for each container to do the same thing  access its content through an index or identifier   we have a different way to do it  which is confusing  In C    each container uses the same way to access its content  thanks to operator overloading     Natural advanced types manipulation The examples below use a Matrix object  found using the first links found on Google for  quot Java Matrix object quot  and  quot C   Matrix object quot      C   YMatrix matrix implementation on CodeProject    http   www codeproject com KB architecture ymatrix aspx    A  B  C  D  E  F are Matrix objects  E    A    B   2    E     A - B     C   D    F    E                       deep copy of the matrix     Java JAMA matrix implementation  seriously        http   math nist gov javanumerics jama doc     A  B  C  D  E  F are Matrix objects  E   A times B times 0 5     E plusEquals A minus B  times C plus D      F   E copy                   deep copy of the matrix  And this is not limited to matrices  The BigInteger and BigDecimal classes of Java suffer from the same confusing verbosity  whereas their equivalents in C   are as clear as built-in types     Natural iterators     C   Random Access iterators   it                       move to the next item --it                       move to the previous item it    5                    move to the next 5th item  random access  value    it                gets the value of the current item  it   3 1415               sets the value 3 1415 to the current item   it  foo                  call method foo   of the current item     Java ListIterator lt E gt   quot bi-directional quot  iterators value   it next            move to the next item  amp  return the value value   it previous        move to the previous item  amp  return the value it set 3 1415              sets the value 3 1415 to the current item     Natural functors     C   Functors myFunctorObject  quot Hello World quot   42        Java Functors     myFunctorObject execute  quot Hello World quot   42        Text concatenation     C   stream handling  with the  lt  lt  operator                      stringStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        fileStream      lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        outputStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        networkStream   lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot    anythingThatOverloadsShiftOperator  lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot        Java concatenation myStringBuffer append  quot Hello  quot   append 25  append  quot  World quot      Ok  in Java you can use MyString    quot Hello  quot    25    quot  World quot    too    But  wait a second  This is operator overloading  isn t it  Isn t it cheating     -D   Generic code  The same generic code modifying operands should be usable both for built-ins primitives  which have no interfaces in Java   standard objects  which could not have the right interface   and user-defined objects  For example  calculating the average value of two values of arbitrary types     C   primitive advanced types template lt typename T gt  T getAverage const T  amp  p lhs  const T  amp  p rhs       return  p lhs   p rhs    2      int     intValue       getAverage 25  42    double  doubleValue    getAverage 25 25  42 42    complex complexValue   getAverage cA  cB       cA  cB are complex Matrix  matrixValue    getAverage mA  mB       mA  mB are Matrix     Java primitive advanced types    It won t really work in Java  even with generics  Sorry    Discussing operator overloading Now that we have seen fair comparisons between C   code using operator overloading  and the same code in Java  we can now discuss  quot operator overloading quot  as a concept    Operator overloading existed since before computers Even outside of computer science  there is operator overloading  For example  in mathematics  operators like    -     etc  are overloaded  Indeed  the signification of    -     etc  changes depending on the types of the operands  numerics  vectors  quantum wave functions  matrices  etc    Most of us  as part of our science courses  learned multiple significations for operators  depending on the types of the operands  Did we find them confusing  them    Operator overloading depends on its operands This is the most important part of operator overloading  Like in mathematics  or in physics  the operation depends on its operands  types  So  know the type of the operand  and you will know the effect of the operation    Even C and Java have  hard-coded  operator overloading In C  the real behavior of an operator will change according to its operands  For example  adding two integers is different than adding two doubles  or even one integer and one double  There is even the whole pointer arithmetic domain  without casting  you can add to a pointer an integer  but you cannot add two pointers      In Java  there is no pointer arithmetic  but someone still found string concatenation without the   operator would be ridiculous enough to justify an exception in the  quot operator overloading is evil quot  creed  It s just that you  as a C  for historical reasons  or Java  for personal reasons  see below  coder  you can t provide your own    In C    operator overloading is not optional    In C    operator overloading for built-in types is not possible  and this is a good thing   but user-defined types can have user-defined operator overloads  As already said earlier  in C    and to the contrary to Java  user-types are not considered second-class citizens of the language  when compared to built-in types  So  if built-in types have operators  user types should be able to have them  too  The truth is that  like the toString    clone    equals   methods are for Java  i e  quasi-standard-like   C   operator overloading is so much part of C   that it becomes as natural as the original C operators  or the before mentioned Java methods  Combined with template programming  operator overloading becomes a well known design pattern  In fact  you cannot go very far in STL without using overloaded operators  and overloading operators for your own class       but it should not be abused Operator overloading should strive to respect the semantics of the operator  Do not subtract in a   operator  as in  quot do not subtract in a add function quot   or  quot return crap in a clone method quot    Cast overloading can be very dangerous because they can lead to ambiguities  So they should really be reserved for well defined cases  As for  amp  amp  and     do not ever overload them unless you really know what you re doing  as you ll lose the the short circuit evaluation that the native operators  amp  amp  and    enjoy   So    Ok    Then why it is not possible in Java  Because James Gosling said so   I left out operator overloading as a fairly personal choice because I had seen too many people abuse it in C    James Gosling  Source  http   www gotw ca publications c family interview htm  Please compare Gosling s text above with Stroustrup s below   Many C   design decisions have their roots in my dislike for forcing people to do things in some particular way       Often  I was tempted to outlaw a feature I personally disliked  I refrained from doing so because I did not think I had the right to force my views on others  Bjarne Stroustrup  Source  The Design and Evolution of C    1 3 General Background     Would operator overloading benefit Java  Some objects would greatly benefit from operator overloading  concrete or numerical types  like BigDecimal  complex numbers  matrices  containers  iterators  comparators  parsers etc    In C    you can profit from this benefit because of Stroustrup s humility  In Java  you re simply screwed because of Gosling s personal choice    Could it be added to Java  The reasons for not adding operator overloading now in Java could be a mix of internal politics  allergy to the feature  distrust of developers  you know  the saboteur ones that seem to haunt Java teams      compatibility with the previous JVMs  time to write a correct specification  etc   So don t hold your breath waiting for this feature      But they do it in C     Yeah    While this is far from being the only difference between the two languages  this one never fails to amuse me  Apparently  the C  folks  with their  quot every primitive is a struct  and a struct derives from Object quot   got it right at first try    And they do it in other languages    Despite all the FUD against used defined operator overloading  the following languages support it  Kotlin  Scala  Dart  Python  F   C   D  Algol 68  Smalltalk  Groovy  Perl 6  C    Ruby  Haskell  MATLAB  Eiffel  Lua  Clojure  Fortran 90  Swift  Ada  Delphi 2005    So many languages  with so many different  and sometimes opposing  philosophies  and yet they all agree on that point  Food for thought

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Well you can really shoot yourself in the foot with operator overloading  It s like with pointers people make stupid mistakes with them and so it was decided to take the scissors away   At least I think that s the reason  I m on your side anyway

User · Answer

James Gosling likened designing Java to the following       There s this principle about moving  when you move from one apartment to another apartment  An interesting experiment is to pack up your apartment and put everything in boxes  then move into the next apartment and not unpack anything until you need it  So you re making your first meal  and you re pulling something out of a box  Then after a month or so you ve used that to pretty much figure out what things in your life you actually need  and then you take the rest of the stuff -- forget how much you like it or how cool it is -- and you just throw it away  It s amazing how that simplifies your life  and you can use that principle in all kinds of design issues  not do things just because they re cool or just because they re interesting     You can read the context of the quote here  Basically operator overloading is great for a class that models some kind of point  currency or complex number  But after that you start running out of examples fast   Another factor was the abuse of the feature in C   by developers overloading operators like   amp  amp          the cast operators and of course  new   The complexity resulting from combining this with pass by value and exceptions is well covered in the Exceptional C   book

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While the Java language does not directly support operator overloading  you can use the Manifold compiler plugin in any Java project to enable it   It supports Java 8 - 13  the current Java version  and is fully supported in IntelliJ IDEA

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Well you can really shoot yourself in the foot with operator overloading  It s like with pointers people make stupid mistakes with them and so it was decided to take the scissors away   At least I think that s the reason  I m on your side anyway

User · Answer

I think this may have been a conscious design choice to force developers to create functions whose names clearly communicate their intentions  In C   developers would overload operators with functionality that would often have no relation to the commonly accepted nature of the given operator  making it nearly impossible to determine what a piece of code does without looking at the definition of the operator

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Saying  that operator overloading leads to logical errors of type that operator does not match the operation logic  it s like saying nothing  The same type of error will occur if function name is inappropriate for operation logic - so what s the solution  drop the ability of function usage     This is a comical answer -  Inappropriate for operation logic   every parameter name  every class  function or whatever can be logicly inappropriate  I think that this option should be available in respectable programing language  and those that think that it s unsafe - hey no bothy says you have to use it   Lets take the C   They drooped the pointers but hey - there is  unsafe code  statement - program as you like on your own risk

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Alternatives to Native Support of Java Operator Overloading  Since Java doesn t have operator overloading  here are some alternatives you can look into    Use another language   Both Groovy and Scala have operator overloading  and are based on Java  Use java-oo  a plugin that enables operator overloading in Java   Note that it is NOT platform independent   Also  it has many issues  and is not compatible with the latest releases of Java  i e  Java 10    Original StackOverflow Source  Use JNI  Java Native Interface  or alternatives   This allows you to write C or C    maybe others   methods for use in Java   Of course this is also NOT platform independent    If anyone is aware of others  please comment  and I will add it to this list

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There are a lot of posts complaining about operator overloading  I felt I had to clarify the  quot operator overloading quot  concepts  offering an alternative viewpoint on this concept   Code obfuscating  This argument is a fallacy    Obfuscating is possible in all languages    It is as easy to obfuscate code in C or Java through functions methods as it is in C   through operator overloads     C   T operator    const T  amp  a  const T  amp  b     add        T c      c value   a value - b value      subtract        return c         Java static T add  T a  T b     add        T c   new T        c value   a value - b value      subtract        return c         C    T add  T a  T b     add           T c      c value   a value - b value      subtract           return c           Even in Java s standard interfaces For another example  let s see the Cloneable interface in Java  You are supposed to clone the object implementing this interface  But you could lie  And create a different object  In fact  this interface is so weak you could return another type of object altogether  just for the fun of it  class MySincereHandShake implements Cloneable       public Object clone                return new MyVengefulKickInYourHead              As the Cloneable interface can be abused obfuscated  should it be banned on the same grounds C   operator overloading is supposed to be  We could overload the toString   method of a MyComplexNumber class to have it return the stringified hour of the day  Should the toString   overloading be banned  too  We could sabotage MyComplexNumber equals to have it return a random value  modify the operands    etc  etc  etc   In Java  as in C    or whatever language  the programmer must respect a minimum of semantics when writing code  This means implementing a add function that adds  and Cloneable implementation method that clones  and a    operator than increments   What s obfuscating anyway  Now that we know that code can be sabotaged even through the pristine Java methods  we can ask ourselves about the real use of operator overloading in C      Clear and natural notation  methods vs  operator overloading  We ll compare below  for different cases  the  quot same quot  code in Java and C    to have an idea of which kind of coding style is clearer     Natural comparisons     C   comparison for built-ins and user-defined types bool    isEqual            A    B   bool    isNotEqual         A    B   bool    isLesser           A  lt   B   bool    isLesserOrEqual    A  lt   B       Java comparison for user-defined types boolean isEqual            A equals B    boolean isNotEqual           A equals B    boolean isLesser           A comparesTo B   lt  0   boolean isLesserOrEqual    A comparesTo B   lt   0    Please note that A and B could be of any type in C    as long as the operator overloads are provided  In Java  when A and B are not primitives  the code can become very confusing  even for primitive-like objects  BigInteger  etc         Natural array container accessors and subscripting     C   container accessors  more natural value          myArray 25               subscript operator value          myVector 25              subscript operator value          myString 25              subscript operator value          myMap  quot 25 quot                subscript operator myArray 25     value                    subscript operator myVector 25    value                    subscript operator myString 25    value                    subscript operator myMap  quot 25 quot      value                    subscript operator     Java container accessors  each one has its special notation value          myArray 25               subscript operator value          myVector get 25          method get value          myString charAt 25       method charAt value          myMap get  quot 25 quot            method get myArray 25     value                    subscript operator myVector set 25  value                  method set myMap put  quot 25 quot   value                   method put  In Java  we see that for each container to do the same thing  access its content through an index or identifier   we have a different way to do it  which is confusing  In C    each container uses the same way to access its content  thanks to operator overloading     Natural advanced types manipulation The examples below use a Matrix object  found using the first links found on Google for  quot Java Matrix object quot  and  quot C   Matrix object quot      C   YMatrix matrix implementation on CodeProject    http   www codeproject com KB architecture ymatrix aspx    A  B  C  D  E  F are Matrix objects  E    A    B   2    E     A - B     C   D    F    E                       deep copy of the matrix     Java JAMA matrix implementation  seriously        http   math nist gov javanumerics jama doc     A  B  C  D  E  F are Matrix objects  E   A times B times 0 5     E plusEquals A minus B  times C plus D      F   E copy                   deep copy of the matrix  And this is not limited to matrices  The BigInteger and BigDecimal classes of Java suffer from the same confusing verbosity  whereas their equivalents in C   are as clear as built-in types     Natural iterators     C   Random Access iterators   it                       move to the next item --it                       move to the previous item it    5                    move to the next 5th item  random access  value    it                gets the value of the current item  it   3 1415               sets the value 3 1415 to the current item   it  foo                  call method foo   of the current item     Java ListIterator lt E gt   quot bi-directional quot  iterators value   it next            move to the next item  amp  return the value value   it previous        move to the previous item  amp  return the value it set 3 1415              sets the value 3 1415 to the current item     Natural functors     C   Functors myFunctorObject  quot Hello World quot   42        Java Functors     myFunctorObject execute  quot Hello World quot   42        Text concatenation     C   stream handling  with the  lt  lt  operator                      stringStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        fileStream      lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        outputStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        networkStream   lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot    anythingThatOverloadsShiftOperator  lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot        Java concatenation myStringBuffer append  quot Hello  quot   append 25  append  quot  World quot      Ok  in Java you can use MyString    quot Hello  quot    25    quot  World quot    too    But  wait a second  This is operator overloading  isn t it  Isn t it cheating     -D   Generic code  The same generic code modifying operands should be usable both for built-ins primitives  which have no interfaces in Java   standard objects  which could not have the right interface   and user-defined objects  For example  calculating the average value of two values of arbitrary types     C   primitive advanced types template lt typename T gt  T getAverage const T  amp  p lhs  const T  amp  p rhs       return  p lhs   p rhs    2      int     intValue       getAverage 25  42    double  doubleValue    getAverage 25 25  42 42    complex complexValue   getAverage cA  cB       cA  cB are complex Matrix  matrixValue    getAverage mA  mB       mA  mB are Matrix     Java primitive advanced types    It won t really work in Java  even with generics  Sorry    Discussing operator overloading Now that we have seen fair comparisons between C   code using operator overloading  and the same code in Java  we can now discuss  quot operator overloading quot  as a concept    Operator overloading existed since before computers Even outside of computer science  there is operator overloading  For example  in mathematics  operators like    -     etc  are overloaded  Indeed  the signification of    -     etc  changes depending on the types of the operands  numerics  vectors  quantum wave functions  matrices  etc    Most of us  as part of our science courses  learned multiple significations for operators  depending on the types of the operands  Did we find them confusing  them    Operator overloading depends on its operands This is the most important part of operator overloading  Like in mathematics  or in physics  the operation depends on its operands  types  So  know the type of the operand  and you will know the effect of the operation    Even C and Java have  hard-coded  operator overloading In C  the real behavior of an operator will change according to its operands  For example  adding two integers is different than adding two doubles  or even one integer and one double  There is even the whole pointer arithmetic domain  without casting  you can add to a pointer an integer  but you cannot add two pointers      In Java  there is no pointer arithmetic  but someone still found string concatenation without the   operator would be ridiculous enough to justify an exception in the  quot operator overloading is evil quot  creed  It s just that you  as a C  for historical reasons  or Java  for personal reasons  see below  coder  you can t provide your own    In C    operator overloading is not optional    In C    operator overloading for built-in types is not possible  and this is a good thing   but user-defined types can have user-defined operator overloads  As already said earlier  in C    and to the contrary to Java  user-types are not considered second-class citizens of the language  when compared to built-in types  So  if built-in types have operators  user types should be able to have them  too  The truth is that  like the toString    clone    equals   methods are for Java  i e  quasi-standard-like   C   operator overloading is so much part of C   that it becomes as natural as the original C operators  or the before mentioned Java methods  Combined with template programming  operator overloading becomes a well known design pattern  In fact  you cannot go very far in STL without using overloaded operators  and overloading operators for your own class       but it should not be abused Operator overloading should strive to respect the semantics of the operator  Do not subtract in a   operator  as in  quot do not subtract in a add function quot   or  quot return crap in a clone method quot    Cast overloading can be very dangerous because they can lead to ambiguities  So they should really be reserved for well defined cases  As for  amp  amp  and     do not ever overload them unless you really know what you re doing  as you ll lose the the short circuit evaluation that the native operators  amp  amp  and    enjoy   So    Ok    Then why it is not possible in Java  Because James Gosling said so   I left out operator overloading as a fairly personal choice because I had seen too many people abuse it in C    James Gosling  Source  http   www gotw ca publications c family interview htm  Please compare Gosling s text above with Stroustrup s below   Many C   design decisions have their roots in my dislike for forcing people to do things in some particular way       Often  I was tempted to outlaw a feature I personally disliked  I refrained from doing so because I did not think I had the right to force my views on others  Bjarne Stroustrup  Source  The Design and Evolution of C    1 3 General Background     Would operator overloading benefit Java  Some objects would greatly benefit from operator overloading  concrete or numerical types  like BigDecimal  complex numbers  matrices  containers  iterators  comparators  parsers etc    In C    you can profit from this benefit because of Stroustrup s humility  In Java  you re simply screwed because of Gosling s personal choice    Could it be added to Java  The reasons for not adding operator overloading now in Java could be a mix of internal politics  allergy to the feature  distrust of developers  you know  the saboteur ones that seem to haunt Java teams      compatibility with the previous JVMs  time to write a correct specification  etc   So don t hold your breath waiting for this feature      But they do it in C     Yeah    While this is far from being the only difference between the two languages  this one never fails to amuse me  Apparently  the C  folks  with their  quot every primitive is a struct  and a struct derives from Object quot   got it right at first try    And they do it in other languages    Despite all the FUD against used defined operator overloading  the following languages support it  Kotlin  Scala  Dart  Python  F   C   D  Algol 68  Smalltalk  Groovy  Perl 6  C    Ruby  Haskell  MATLAB  Eiffel  Lua  Clojure  Fortran 90  Swift  Ada  Delphi 2005    So many languages  with so many different  and sometimes opposing  philosophies  and yet they all agree on that point  Food for thought

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James Gosling likened designing Java to the following       There s this principle about moving  when you move from one apartment to another apartment  An interesting experiment is to pack up your apartment and put everything in boxes  then move into the next apartment and not unpack anything until you need it  So you re making your first meal  and you re pulling something out of a box  Then after a month or so you ve used that to pretty much figure out what things in your life you actually need  and then you take the rest of the stuff -- forget how much you like it or how cool it is -- and you just throw it away  It s amazing how that simplifies your life  and you can use that principle in all kinds of design issues  not do things just because they re cool or just because they re interesting     You can read the context of the quote here  Basically operator overloading is great for a class that models some kind of point  currency or complex number  But after that you start running out of examples fast   Another factor was the abuse of the feature in C   by developers overloading operators like   amp  amp          the cast operators and of course  new   The complexity resulting from combining this with pass by value and exceptions is well covered in the Exceptional C   book

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James Gosling likened designing Java to the following       There s this principle about moving  when you move from one apartment to another apartment  An interesting experiment is to pack up your apartment and put everything in boxes  then move into the next apartment and not unpack anything until you need it  So you re making your first meal  and you re pulling something out of a box  Then after a month or so you ve used that to pretty much figure out what things in your life you actually need  and then you take the rest of the stuff -- forget how much you like it or how cool it is -- and you just throw it away  It s amazing how that simplifies your life  and you can use that principle in all kinds of design issues  not do things just because they re cool or just because they re interesting     You can read the context of the quote here  Basically operator overloading is great for a class that models some kind of point  currency or complex number  But after that you start running out of examples fast   Another factor was the abuse of the feature in C   by developers overloading operators like   amp  amp          the cast operators and of course  new   The complexity resulting from combining this with pass by value and exceptions is well covered in the Exceptional C   book

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Some people say that operator overloading in Java would lead to obsfuscation  Have those people ever stopped to look at some Java code doing some basic maths like increasing a financial value by a percentage using BigDecimal        the verbosity of such an exercise becomes its own demonstration of obsfuscation  Ironically  adding operator overloading to Java would allow us to create our own Currency class which would make such mathematical code elegant and simple  less obsfuscated

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The Java designers decided that operator overloading was more trouble than it was worth  Simple as that   In a language where every object variable is actually a reference  operator overloading gets the additional hazard of being quite illogical - to a C   programmer at least  Compare the situation with C  s    operator overloading and Object Equals and Object ReferenceEquals  or whatever it s called

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Assuming you wanted to overwrite the previous value of the object referred to by a  then a member function would have to be invoked   Complex a  b  c         a   b add c     In C    this expression tells the compiler to create three  3  objects on the stack  perform addition  and copy the resultant value from the temporary object into the existing object a   However  in Java  operator  doesn t perform value copy for reference types  and users can only create new reference types  not value types  So for a user-defined type named Complex  assignment means to copy a reference to an existing value   Consider instead   b set 1  0      initialize to real number  1  a   b   b set 2  0   assert   a equals b        this assertion will fail   In C    this copies the value  so the comparison will result not-equal  In Java  operator  performs reference copy  so a and b are now referring to the same value  As a result  the comparison will produce  equal   since the object will compare equal to itself   The difference between copies and references only adds to the confusion of operator overloading  As  Sebastian mentioned  Java and C  both have to deal with value and reference equality separately -- operator  would likely deal with values and objects  but operator  is already implemented to deal with references   In C    you should only be dealing with one kind of comparison at a time  so it can be less confusing  For example  on Complex  operator  and operator   are both working on values -- copying values and comparing values respectively

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Sometimes it would be nice to have operator overloading  friend classes and multiple inheritance   However I still think it was a good decision  If Java would have had operator overloading then we could never be sure of operator meanings without looking through source code  At present that s not necessary  And I think your example of using methods instead of operator overloading is also quite readable  If you want to make things more clear you could always add a comment above hairy statements      a   b   c Complex a  b  c  a   b add c

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Check out Boost Units  link text  It provides zero-overhead Dimensional analysis through operator overloading  How much clearer can this get   quantity lt force gt      F   2 0 newton  quantity lt length gt     dx   2 0 meter  quantity lt energy gt     E   F   dx  std  cout  lt  lt   Energy      lt  lt  E  lt  lt  endl    would actually output  Energy   4 J  which is correct

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Well you can really shoot yourself in the foot with operator overloading  It s like with pointers people make stupid mistakes with them and so it was decided to take the scissors away   At least I think that s the reason  I m on your side anyway

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I think this may have been a conscious design choice to force developers to create functions whose names clearly communicate their intentions  In C   developers would overload operators with functionality that would often have no relation to the commonly accepted nature of the given operator  making it nearly impossible to determine what a piece of code does without looking at the definition of the operator

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Check out Boost Units  link text  It provides zero-overhead Dimensional analysis through operator overloading  How much clearer can this get   quantity lt force gt      F   2 0 newton  quantity lt length gt     dx   2 0 meter  quantity lt energy gt     E   F   dx  std  cout  lt  lt   Energy      lt  lt  E  lt  lt  endl    would actually output  Energy   4 J  which is correct

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There are a lot of posts complaining about operator overloading  I felt I had to clarify the  quot operator overloading quot  concepts  offering an alternative viewpoint on this concept   Code obfuscating  This argument is a fallacy    Obfuscating is possible in all languages    It is as easy to obfuscate code in C or Java through functions methods as it is in C   through operator overloads     C   T operator    const T  amp  a  const T  amp  b     add        T c      c value   a value - b value      subtract        return c         Java static T add  T a  T b     add        T c   new T        c value   a value - b value      subtract        return c         C    T add  T a  T b     add           T c      c value   a value - b value      subtract           return c           Even in Java s standard interfaces For another example  let s see the Cloneable interface in Java  You are supposed to clone the object implementing this interface  But you could lie  And create a different object  In fact  this interface is so weak you could return another type of object altogether  just for the fun of it  class MySincereHandShake implements Cloneable       public Object clone                return new MyVengefulKickInYourHead              As the Cloneable interface can be abused obfuscated  should it be banned on the same grounds C   operator overloading is supposed to be  We could overload the toString   method of a MyComplexNumber class to have it return the stringified hour of the day  Should the toString   overloading be banned  too  We could sabotage MyComplexNumber equals to have it return a random value  modify the operands    etc  etc  etc   In Java  as in C    or whatever language  the programmer must respect a minimum of semantics when writing code  This means implementing a add function that adds  and Cloneable implementation method that clones  and a    operator than increments   What s obfuscating anyway  Now that we know that code can be sabotaged even through the pristine Java methods  we can ask ourselves about the real use of operator overloading in C      Clear and natural notation  methods vs  operator overloading  We ll compare below  for different cases  the  quot same quot  code in Java and C    to have an idea of which kind of coding style is clearer     Natural comparisons     C   comparison for built-ins and user-defined types bool    isEqual            A    B   bool    isNotEqual         A    B   bool    isLesser           A  lt   B   bool    isLesserOrEqual    A  lt   B       Java comparison for user-defined types boolean isEqual            A equals B    boolean isNotEqual           A equals B    boolean isLesser           A comparesTo B   lt  0   boolean isLesserOrEqual    A comparesTo B   lt   0    Please note that A and B could be of any type in C    as long as the operator overloads are provided  In Java  when A and B are not primitives  the code can become very confusing  even for primitive-like objects  BigInteger  etc         Natural array container accessors and subscripting     C   container accessors  more natural value          myArray 25               subscript operator value          myVector 25              subscript operator value          myString 25              subscript operator value          myMap  quot 25 quot                subscript operator myArray 25     value                    subscript operator myVector 25    value                    subscript operator myString 25    value                    subscript operator myMap  quot 25 quot      value                    subscript operator     Java container accessors  each one has its special notation value          myArray 25               subscript operator value          myVector get 25          method get value          myString charAt 25       method charAt value          myMap get  quot 25 quot            method get myArray 25     value                    subscript operator myVector set 25  value                  method set myMap put  quot 25 quot   value                   method put  In Java  we see that for each container to do the same thing  access its content through an index or identifier   we have a different way to do it  which is confusing  In C    each container uses the same way to access its content  thanks to operator overloading     Natural advanced types manipulation The examples below use a Matrix object  found using the first links found on Google for  quot Java Matrix object quot  and  quot C   Matrix object quot      C   YMatrix matrix implementation on CodeProject    http   www codeproject com KB architecture ymatrix aspx    A  B  C  D  E  F are Matrix objects  E    A    B   2    E     A - B     C   D    F    E                       deep copy of the matrix     Java JAMA matrix implementation  seriously        http   math nist gov javanumerics jama doc     A  B  C  D  E  F are Matrix objects  E   A times B times 0 5     E plusEquals A minus B  times C plus D      F   E copy                   deep copy of the matrix  And this is not limited to matrices  The BigInteger and BigDecimal classes of Java suffer from the same confusing verbosity  whereas their equivalents in C   are as clear as built-in types     Natural iterators     C   Random Access iterators   it                       move to the next item --it                       move to the previous item it    5                    move to the next 5th item  random access  value    it                gets the value of the current item  it   3 1415               sets the value 3 1415 to the current item   it  foo                  call method foo   of the current item     Java ListIterator lt E gt   quot bi-directional quot  iterators value   it next            move to the next item  amp  return the value value   it previous        move to the previous item  amp  return the value it set 3 1415              sets the value 3 1415 to the current item     Natural functors     C   Functors myFunctorObject  quot Hello World quot   42        Java Functors     myFunctorObject execute  quot Hello World quot   42        Text concatenation     C   stream handling  with the  lt  lt  operator                      stringStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        fileStream      lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        outputStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        networkStream   lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot    anythingThatOverloadsShiftOperator  lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot        Java concatenation myStringBuffer append  quot Hello  quot   append 25  append  quot  World quot      Ok  in Java you can use MyString    quot Hello  quot    25    quot  World quot    too    But  wait a second  This is operator overloading  isn t it  Isn t it cheating     -D   Generic code  The same generic code modifying operands should be usable both for built-ins primitives  which have no interfaces in Java   standard objects  which could not have the right interface   and user-defined objects  For example  calculating the average value of two values of arbitrary types     C   primitive advanced types template lt typename T gt  T getAverage const T  amp  p lhs  const T  amp  p rhs       return  p lhs   p rhs    2      int     intValue       getAverage 25  42    double  doubleValue    getAverage 25 25  42 42    complex complexValue   getAverage cA  cB       cA  cB are complex Matrix  matrixValue    getAverage mA  mB       mA  mB are Matrix     Java primitive advanced types    It won t really work in Java  even with generics  Sorry    Discussing operator overloading Now that we have seen fair comparisons between C   code using operator overloading  and the same code in Java  we can now discuss  quot operator overloading quot  as a concept    Operator overloading existed since before computers Even outside of computer science  there is operator overloading  For example  in mathematics  operators like    -     etc  are overloaded  Indeed  the signification of    -     etc  changes depending on the types of the operands  numerics  vectors  quantum wave functions  matrices  etc    Most of us  as part of our science courses  learned multiple significations for operators  depending on the types of the operands  Did we find them confusing  them    Operator overloading depends on its operands This is the most important part of operator overloading  Like in mathematics  or in physics  the operation depends on its operands  types  So  know the type of the operand  and you will know the effect of the operation    Even C and Java have  hard-coded  operator overloading In C  the real behavior of an operator will change according to its operands  For example  adding two integers is different than adding two doubles  or even one integer and one double  There is even the whole pointer arithmetic domain  without casting  you can add to a pointer an integer  but you cannot add two pointers      In Java  there is no pointer arithmetic  but someone still found string concatenation without the   operator would be ridiculous enough to justify an exception in the  quot operator overloading is evil quot  creed  It s just that you  as a C  for historical reasons  or Java  for personal reasons  see below  coder  you can t provide your own    In C    operator overloading is not optional    In C    operator overloading for built-in types is not possible  and this is a good thing   but user-defined types can have user-defined operator overloads  As already said earlier  in C    and to the contrary to Java  user-types are not considered second-class citizens of the language  when compared to built-in types  So  if built-in types have operators  user types should be able to have them  too  The truth is that  like the toString    clone    equals   methods are for Java  i e  quasi-standard-like   C   operator overloading is so much part of C   that it becomes as natural as the original C operators  or the before mentioned Java methods  Combined with template programming  operator overloading becomes a well known design pattern  In fact  you cannot go very far in STL without using overloaded operators  and overloading operators for your own class       but it should not be abused Operator overloading should strive to respect the semantics of the operator  Do not subtract in a   operator  as in  quot do not subtract in a add function quot   or  quot return crap in a clone method quot    Cast overloading can be very dangerous because they can lead to ambiguities  So they should really be reserved for well defined cases  As for  amp  amp  and     do not ever overload them unless you really know what you re doing  as you ll lose the the short circuit evaluation that the native operators  amp  amp  and    enjoy   So    Ok    Then why it is not possible in Java  Because James Gosling said so   I left out operator overloading as a fairly personal choice because I had seen too many people abuse it in C    James Gosling  Source  http   www gotw ca publications c family interview htm  Please compare Gosling s text above with Stroustrup s below   Many C   design decisions have their roots in my dislike for forcing people to do things in some particular way       Often  I was tempted to outlaw a feature I personally disliked  I refrained from doing so because I did not think I had the right to force my views on others  Bjarne Stroustrup  Source  The Design and Evolution of C    1 3 General Background     Would operator overloading benefit Java  Some objects would greatly benefit from operator overloading  concrete or numerical types  like BigDecimal  complex numbers  matrices  containers  iterators  comparators  parsers etc    In C    you can profit from this benefit because of Stroustrup s humility  In Java  you re simply screwed because of Gosling s personal choice    Could it be added to Java  The reasons for not adding operator overloading now in Java could be a mix of internal politics  allergy to the feature  distrust of developers  you know  the saboteur ones that seem to haunt Java teams      compatibility with the previous JVMs  time to write a correct specification  etc   So don t hold your breath waiting for this feature      But they do it in C     Yeah    While this is far from being the only difference between the two languages  this one never fails to amuse me  Apparently  the C  folks  with their  quot every primitive is a struct  and a struct derives from Object quot   got it right at first try    And they do it in other languages    Despite all the FUD against used defined operator overloading  the following languages support it  Kotlin  Scala  Dart  Python  F   C   D  Algol 68  Smalltalk  Groovy  Perl 6  C    Ruby  Haskell  MATLAB  Eiffel  Lua  Clojure  Fortran 90  Swift  Ada  Delphi 2005    So many languages  with so many different  and sometimes opposing  philosophies  and yet they all agree on that point  Food for thought

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I think this may have been a conscious design choice to force developers to create functions whose names clearly communicate their intentions  In C   developers would overload operators with functionality that would often have no relation to the commonly accepted nature of the given operator  making it nearly impossible to determine what a piece of code does without looking at the definition of the operator

User · Answer

Some people say that operator overloading in Java would lead to obsfuscation  Have those people ever stopped to look at some Java code doing some basic maths like increasing a financial value by a percentage using BigDecimal        the verbosity of such an exercise becomes its own demonstration of obsfuscation  Ironically  adding operator overloading to Java would allow us to create our own Currency class which would make such mathematical code elegant and simple  less obsfuscated

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There are a lot of posts complaining about operator overloading  I felt I had to clarify the  quot operator overloading quot  concepts  offering an alternative viewpoint on this concept   Code obfuscating  This argument is a fallacy    Obfuscating is possible in all languages    It is as easy to obfuscate code in C or Java through functions methods as it is in C   through operator overloads     C   T operator    const T  amp  a  const T  amp  b     add        T c      c value   a value - b value      subtract        return c         Java static T add  T a  T b     add        T c   new T        c value   a value - b value      subtract        return c         C    T add  T a  T b     add           T c      c value   a value - b value      subtract           return c           Even in Java s standard interfaces For another example  let s see the Cloneable interface in Java  You are supposed to clone the object implementing this interface  But you could lie  And create a different object  In fact  this interface is so weak you could return another type of object altogether  just for the fun of it  class MySincereHandShake implements Cloneable       public Object clone                return new MyVengefulKickInYourHead              As the Cloneable interface can be abused obfuscated  should it be banned on the same grounds C   operator overloading is supposed to be  We could overload the toString   method of a MyComplexNumber class to have it return the stringified hour of the day  Should the toString   overloading be banned  too  We could sabotage MyComplexNumber equals to have it return a random value  modify the operands    etc  etc  etc   In Java  as in C    or whatever language  the programmer must respect a minimum of semantics when writing code  This means implementing a add function that adds  and Cloneable implementation method that clones  and a    operator than increments   What s obfuscating anyway  Now that we know that code can be sabotaged even through the pristine Java methods  we can ask ourselves about the real use of operator overloading in C      Clear and natural notation  methods vs  operator overloading  We ll compare below  for different cases  the  quot same quot  code in Java and C    to have an idea of which kind of coding style is clearer     Natural comparisons     C   comparison for built-ins and user-defined types bool    isEqual            A    B   bool    isNotEqual         A    B   bool    isLesser           A  lt   B   bool    isLesserOrEqual    A  lt   B       Java comparison for user-defined types boolean isEqual            A equals B    boolean isNotEqual           A equals B    boolean isLesser           A comparesTo B   lt  0   boolean isLesserOrEqual    A comparesTo B   lt   0    Please note that A and B could be of any type in C    as long as the operator overloads are provided  In Java  when A and B are not primitives  the code can become very confusing  even for primitive-like objects  BigInteger  etc         Natural array container accessors and subscripting     C   container accessors  more natural value          myArray 25               subscript operator value          myVector 25              subscript operator value          myString 25              subscript operator value          myMap  quot 25 quot                subscript operator myArray 25     value                    subscript operator myVector 25    value                    subscript operator myString 25    value                    subscript operator myMap  quot 25 quot      value                    subscript operator     Java container accessors  each one has its special notation value          myArray 25               subscript operator value          myVector get 25          method get value          myString charAt 25       method charAt value          myMap get  quot 25 quot            method get myArray 25     value                    subscript operator myVector set 25  value                  method set myMap put  quot 25 quot   value                   method put  In Java  we see that for each container to do the same thing  access its content through an index or identifier   we have a different way to do it  which is confusing  In C    each container uses the same way to access its content  thanks to operator overloading     Natural advanced types manipulation The examples below use a Matrix object  found using the first links found on Google for  quot Java Matrix object quot  and  quot C   Matrix object quot      C   YMatrix matrix implementation on CodeProject    http   www codeproject com KB architecture ymatrix aspx    A  B  C  D  E  F are Matrix objects  E    A    B   2    E     A - B     C   D    F    E                       deep copy of the matrix     Java JAMA matrix implementation  seriously        http   math nist gov javanumerics jama doc     A  B  C  D  E  F are Matrix objects  E   A times B times 0 5     E plusEquals A minus B  times C plus D      F   E copy                   deep copy of the matrix  And this is not limited to matrices  The BigInteger and BigDecimal classes of Java suffer from the same confusing verbosity  whereas their equivalents in C   are as clear as built-in types     Natural iterators     C   Random Access iterators   it                       move to the next item --it                       move to the previous item it    5                    move to the next 5th item  random access  value    it                gets the value of the current item  it   3 1415               sets the value 3 1415 to the current item   it  foo                  call method foo   of the current item     Java ListIterator lt E gt   quot bi-directional quot  iterators value   it next            move to the next item  amp  return the value value   it previous        move to the previous item  amp  return the value it set 3 1415              sets the value 3 1415 to the current item     Natural functors     C   Functors myFunctorObject  quot Hello World quot   42        Java Functors     myFunctorObject execute  quot Hello World quot   42        Text concatenation     C   stream handling  with the  lt  lt  operator                      stringStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        fileStream      lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        outputStream    lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot                        networkStream   lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot    anythingThatOverloadsShiftOperator  lt  lt   quot Hello  quot   lt  lt  25  lt  lt   quot  World quot        Java concatenation myStringBuffer append  quot Hello  quot   append 25  append  quot  World quot      Ok  in Java you can use MyString    quot Hello  quot    25    quot  World quot    too    But  wait a second  This is operator overloading  isn t it  Isn t it cheating     -D   Generic code  The same generic code modifying operands should be usable both for built-ins primitives  which have no interfaces in Java   standard objects  which could not have the right interface   and user-defined objects  For example  calculating the average value of two values of arbitrary types     C   primitive advanced types template lt typename T gt  T getAverage const T  amp  p lhs  const T  amp  p rhs       return  p lhs   p rhs    2      int     intValue       getAverage 25  42    double  doubleValue    getAverage 25 25  42 42    complex complexValue   getAverage cA  cB       cA  cB are complex Matrix  matrixValue    getAverage mA  mB       mA  mB are Matrix     Java primitive advanced types    It won t really work in Java  even with generics  Sorry    Discussing operator overloading Now that we have seen fair comparisons between C   code using operator overloading  and the same code in Java  we can now discuss  quot operator overloading quot  as a concept    Operator overloading existed since before computers Even outside of computer science  there is operator overloading  For example  in mathematics  operators like    -     etc  are overloaded  Indeed  the signification of    -     etc  changes depending on the types of the operands  numerics  vectors  quantum wave functions  matrices  etc    Most of us  as part of our science courses  learned multiple significations for operators  depending on the types of the operands  Did we find them confusing  them    Operator overloading depends on its operands This is the most important part of operator overloading  Like in mathematics  or in physics  the operation depends on its operands  types  So  know the type of the operand  and you will know the effect of the operation    Even C and Java have  hard-coded  operator overloading In C  the real behavior of an operator will change according to its operands  For example  adding two integers is different than adding two doubles  or even one integer and one double  There is even the whole pointer arithmetic domain  without casting  you can add to a pointer an integer  but you cannot add two pointers      In Java  there is no pointer arithmetic  but someone still found string concatenation without the   operator would be ridiculous enough to justify an exception in the  quot operator overloading is evil quot  creed  It s just that you  as a C  for historical reasons  or Java  for personal reasons  see below  coder  you can t provide your own    In C    operator overloading is not optional    In C    operator overloading for built-in types is not possible  and this is a good thing   but user-defined types can have user-defined operator overloads  As already said earlier  in C    and to the contrary to Java  user-types are not considered second-class citizens of the language  when compared to built-in types  So  if built-in types have operators  user types should be able to have them  too  The truth is that  like the toString    clone    equals   methods are for Java  i e  quasi-standard-like   C   operator overloading is so much part of C   that it becomes as natural as the original C operators  or the before mentioned Java methods  Combined with template programming  operator overloading becomes a well known design pattern  In fact  you cannot go very far in STL without using overloaded operators  and overloading operators for your own class       but it should not be abused Operator overloading should strive to respect the semantics of the operator  Do not subtract in a   operator  as in  quot do not subtract in a add function quot   or  quot return crap in a clone method quot    Cast overloading can be very dangerous because they can lead to ambiguities  So they should really be reserved for well defined cases  As for  amp  amp  and     do not ever overload them unless you really know what you re doing  as you ll lose the the short circuit evaluation that the native operators  amp  amp  and    enjoy   So    Ok    Then why it is not possible in Java  Because James Gosling said so   I left out operator overloading as a fairly personal choice because I had seen too many people abuse it in C    James Gosling  Source  http   www gotw ca publications c family interview htm  Please compare Gosling s text above with Stroustrup s below   Many C   design decisions have their roots in my dislike for forcing people to do things in some particular way       Often  I was tempted to outlaw a feature I personally disliked  I refrained from doing so because I did not think I had the right to force my views on others  Bjarne Stroustrup  Source  The Design and Evolution of C    1 3 General Background     Would operator overloading benefit Java  Some objects would greatly benefit from operator overloading  concrete or numerical types  like BigDecimal  complex numbers  matrices  containers  iterators  comparators  parsers etc    In C    you can profit from this benefit because of Stroustrup s humility  In Java  you re simply screwed because of Gosling s personal choice    Could it be added to Java  The reasons for not adding operator overloading now in Java could be a mix of internal politics  allergy to the feature  distrust of developers  you know  the saboteur ones that seem to haunt Java teams      compatibility with the previous JVMs  time to write a correct specification  etc   So don t hold your breath waiting for this feature      But they do it in C     Yeah    While this is far from being the only difference between the two languages  this one never fails to amuse me  Apparently  the C  folks  with their  quot every primitive is a struct  and a struct derives from Object quot   got it right at first try    And they do it in other languages    Despite all the FUD against used defined operator overloading  the following languages support it  Kotlin  Scala  Dart  Python  F   C   D  Algol 68  Smalltalk  Groovy  Perl 6  C    Ruby  Haskell  MATLAB  Eiffel  Lua  Clojure  Fortran 90  Swift  Ada  Delphi 2005    So many languages  with so many different  and sometimes opposing  philosophies  and yet they all agree on that point  Food for thought

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Check out Boost Units  link text  It provides zero-overhead Dimensional analysis through operator overloading  How much clearer can this get   quantity lt force gt      F   2 0 newton  quantity lt length gt     dx   2 0 meter  quantity lt energy gt     E   F   dx  std  cout  lt  lt   Energy      lt  lt  E  lt  lt  endl    would actually output  Energy   4 J  which is correct

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Assuming Java as the implementation language then a  b  and c would all be references to type Complex with initial values of null  Also assuming that Complex is immutable as the mentioned BigInteger and similar immutable BigDecimal  I d I think you mean the following  as you re assigning the reference to the Complex returned from adding b and c  and not comparing this reference to a      Isn t    Complex a  b  c  a   b   c        much simpler than   Complex a  b  c  a   b add c

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I think this may have been a conscious design choice to force developers to create functions whose names clearly communicate their intentions  In C   developers would overload operators with functionality that would often have no relation to the commonly accepted nature of the given operator  making it nearly impossible to determine what a piece of code does without looking at the definition of the operator

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Assuming Java as the implementation language then a  b  and c would all be references to type Complex with initial values of null  Also assuming that Complex is immutable as the mentioned BigInteger and similar immutable BigDecimal  I d I think you mean the following  as you re assigning the reference to the Complex returned from adding b and c  and not comparing this reference to a      Isn t    Complex a  b  c  a   b   c        much simpler than   Complex a  b  c  a   b add c

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Sometimes it would be nice to have operator overloading  friend classes and multiple inheritance   However I still think it was a good decision  If Java would have had operator overloading then we could never be sure of operator meanings without looking through source code  At present that s not necessary  And I think your example of using methods instead of operator overloading is also quite readable  If you want to make things more clear you could always add a comment above hairy statements      a   b   c Complex a  b  c  a   b add c

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Groovy has operator overloading  and runs in the JVM  If you don t mind the performance hit  which gets smaller everyday   It s automatic based on method names  e g       calls the  plus argument   method

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Groovy has operator overloading  and runs in the JVM  If you don t mind the performance hit  which gets smaller everyday   It s automatic based on method names  e g       calls the  plus argument   method

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The Java designers decided that operator overloading was more trouble than it was worth  Simple as that   In a language where every object variable is actually a reference  operator overloading gets the additional hazard of being quite illogical - to a C   programmer at least  Compare the situation with C  s    operator overloading and Object Equals and Object ReferenceEquals  or whatever it s called

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Sometimes it would be nice to have operator overloading  friend classes and multiple inheritance   However I still think it was a good decision  If Java would have had operator overloading then we could never be sure of operator meanings without looking through source code  At present that s not necessary  And I think your example of using methods instead of operator overloading is also quite readable  If you want to make things more clear you could always add a comment above hairy statements      a   b   c Complex a  b  c  a   b add c

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This is not a good reason to disallow it but a practical one   People do not always use it responsibly  Look at this example from the Python library scapy    gt  gt  gt  IP    lt IP   gt   gt  gt  gt  IP   TCP    lt IP frag 0 proto TCP   lt TCP   gt  gt   gt  gt  gt  Ether   IP   TCP    lt Ether type 0x800   lt IP frag 0 proto TCP   lt TCP   gt  gt  gt   gt  gt  gt  IP   TCP    GET   HTTP 1 0 r n r n   lt IP frag 0 proto TCP   lt TCP   lt Raw load  GET   HTTP 1 0 r n r n    gt  gt  gt   gt  gt  gt  Ether   IP   IP   UDP    lt Ether type 0x800   lt IP frag 0 proto IP   lt IP frag 0 proto UDP   lt UDP   gt  gt  gt  gt   gt  gt  gt  IP proto 55  TCP    lt IP frag 0 proto 55   lt TCP   gt  gt    Here is the explanation      The   operator has been used as a composition operator between two   layers  When doing so  the lower layer can have one or more of its   defaults fields overloaded according to the upper layer   You still   can give the value you want   A string can be used as a raw layer

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Sometimes it would be nice to have operator overloading  friend classes and multiple inheritance   However I still think it was a good decision  If Java would have had operator overloading then we could never be sure of operator meanings without looking through source code  At present that s not necessary  And I think your example of using methods instead of operator overloading is also quite readable  If you want to make things more clear you could always add a comment above hairy statements      a   b   c Complex a  b  c  a   b add c

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I think that people making decisions simply forgot about complex values   matrix algebra  set theory and other cases when overloading would allow to use the standard notation without building everything into the language  Anyway  only mathematically oriented software really benefits from such features  A generic customer application almost never needs them  They arguments about the unnecessary obfuscation are obviously valid when a programmer defines some program-specific operator where it could be the function instead  A name of the function  when clearly visible  provides the hint that it does  Operator is a function without the readable name  Java is generally designed about philosophy that some extra verbosity is not bad as it makes the code more readable  Constructs that do the same just have less code to type in used to be called a  quot syntax sugar quot  in the past  This is very different from the Python philosophy  for instance  where shorter is near always seen as better  even if providing less context for the second reader

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Assuming Java as the implementation language then a  b  and c would all be references to type Complex with initial values of null  Also assuming that Complex is immutable as the mentioned BigInteger and similar immutable BigDecimal  I d I think you mean the following  as you re assigning the reference to the Complex returned from adding b and c  and not comparing this reference to a      Isn t    Complex a  b  c  a   b   c        much simpler than   Complex a  b  c  a   b add c

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Groovy has operator overloading  and runs in the JVM  If you don t mind the performance hit  which gets smaller everyday   It s automatic based on method names  e g       calls the  plus argument   method

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The Java designers decided that operator overloading was more trouble than it was worth  Simple as that   In a language where every object variable is actually a reference  operator overloading gets the additional hazard of being quite illogical - to a C   programmer at least  Compare the situation with C  s    operator overloading and Object Equals and Object ReferenceEquals  or whatever it s called

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While the Java language does not directly support operator overloading  you can use the Manifold compiler plugin in any Java project to enable it   It supports Java 8 - 13  the current Java version  and is fully supported in IntelliJ IDEA

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Check out Boost Units  link text  It provides zero-overhead Dimensional analysis through operator overloading  How much clearer can this get   quantity lt force gt      F   2 0 newton  quantity lt length gt     dx   2 0 meter  quantity lt energy gt     E   F   dx  std  cout  lt  lt   Energy      lt  lt  E  lt  lt  endl    would actually output  Energy   4 J  which is correct

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Alternatives to Native Support of Java Operator Overloading  Since Java doesn t have operator overloading  here are some alternatives you can look into    Use another language   Both Groovy and Scala have operator overloading  and are based on Java  Use java-oo  a plugin that enables operator overloading in Java   Note that it is NOT platform independent   Also  it has many issues  and is not compatible with the latest releases of Java  i e  Java 10    Original StackOverflow Source  Use JNI  Java Native Interface  or alternatives   This allows you to write C or C    maybe others   methods for use in Java   Of course this is also NOT platform independent    If anyone is aware of others  please comment  and I will add it to this list

[java] Why doesn't Java offer operator overloading?

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Examples related to operator-overloading