What is the difference between an int and an Integer in Java and C

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I was reading More Joel on Software when I came across Joel Spolsky saying something about a particular type of programmer knowing the difference between an int and an Integer in Java C   Object-Oriented Programming Languages    So  what is the difference

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An int and Integer in Java and C  are two different terms used to represent different things  It is one of the the primitive data types that can be assigned to a variable that can store exactly  One value of its declared type at a time   For example   int number   7    Where int is the datatype assigned to the variable number which holds the value seven  So an int is just a primitive not an object   While an Integer is a wrapper class for a primitive data type which has static methods  That can be used as an argument to a method which requires an object  where as int can be used as an argument to a method which requires an integer value  that can be used for arithmetic expression    For example   Integer number   new Integer 5

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Regarding Java 1 5 and autoboxing there is an important  quirk  that comes to play when comparing Integer objects   In Java  Integer objects with the values -128 to 127 are immutable  that is  for one particular integer value  say 23  all Integer objects instantiated through your program with the value 23 points to the exact same object    Example  this returns true   Integer i1   new Integer 127   Integer i2   new Integer 127   System out println i1    i2       true   While this returns false   Integer i1   new Integer 128   Integer i2   new Integer 128   System out println i1    i2       false   The    compares by reference  does the variables point to the same object    This result may or may not differ depending on what JVM you are using  The specification autoboxing for Java 1 5 requires that integers  -128 to 127  always box to the same wrapper object    A solution     One should always use the Integer equals   method when comparing Integer objects   System out println i1 equals i2        true   More info at java net Example at bexhuff com

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In both languages  Java and C   int is 4-byte signed integer   Unlike Java  C  Provides both signed and unsigned integer values  As Java and C  are object object-oriented  some operations in these languages do not map directly onto instructions provided by the run time and so needs to be defined as part of an object of some type   C  provides System Int32 which is a value type using a part of  memory that belongs to the reference type on the heap   java provides java lang Integer which is a reference type operating on int  The methods in Integer can t be compiled directly to run time instructions So we box an int value to convert it into an instance of Integer and use the methods which expects instance of some type  like toString    parseInt    valueOf   etc    In C  variable  int refers to System Int32 Any 4-byte value in memory can be interpreted as a primitive int  that can be manipulated by  instance of System Int32 So int is an alias for System Int32 When using integer-related methods like int Parse    int ToString   etc  Integer is compiled into the FCL System Int32 struct calling the respective methods like Int32 Parse    Int32 ToString

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01  Integer can be null  But int cannot be null   Integer value1   null    OK  int value2   null        Error   02  Only can pass Wrapper Classes type values to any collection class    Wrapper Classes - Boolean Character Byte Short Integer Long Float Double   List lt Integer gt  element   new ArrayList lt  gt     int valueInt   10  Integer  valueInteger   new Integer value   element add valueInteger     But normally we add primitive values to collection class  Is point 02 correct   List lt Integer gt  element   new ArrayList lt  gt     element add 5     Yes 02 is correct  beacouse autoboxing      Autoboxing is the automatic conversion that the java compiler makes   between the primitive type and their corresponding wrapper class    Then 5 convert as Integer value by autoboxing

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One more thing that I don t see in previous answers  In Java the primitive wrappers classes like Integer  Double  Float  Boolean    and String are suposed to be invariant  so that when you pass an instance of those classes the invoked method couldn t alter your data in any way  in opositi  n with most of other classes  which internal data could be altered by its public methods  So that this classes only has  getter  methods  no  setters   besides the constructor   In a java program String literals are stored in a separate portion of heap memory  only a instance for literal  to save memory reusing those instances

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I ll add to the excellent answers given above  and talk about boxing and unboxing  and how this applies to Java  although C  has it too   I ll use just Java terminology because I am more au fait with that   As the answers mentioned  int is just a number  called the unboxed type   whereas Integer is an object  which contains the number  hence a boxed type   In Java terms  that means  apart from not being able to call methods on int   you cannot store int or other non-object types in collections  List  Map  etc    In order to store them  you must first box them up in its corresponding boxed type   Java 5 onwards have something called auto-boxing and auto-unboxing which allow the boxing unboxing to be done behind the scenes  Compare and contrast  Java 5 version   Deque lt Integer gt  queue   void add int n        queue add n      int remove         return queue remove        Java 1 4 or earlier  no generics either    Deque queue   void add int n        queue add Integer valueOf n       int remove         return   Integer  queue remove    intValue        It must be noted that despite the brevity in the Java 5 version  both versions generate identical bytecode  Thus  although auto-boxing and auto-unboxing are very convenient because you write less code  these operations do happens behind the scenes  with the same runtime costs  so you still have to be aware of their existence   Hope this helps

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An int variable holds a 32 bit signed integer value  An Integer  with capital I  holds a reference to an object of  class  type Integer  or to null   Java automatically casts between the two  from Integer to int whenever the Integer object occurs as an argument to an int operator or is assigned to an int variable  or an int value is assigned to an Integer variable  This casting is called boxing unboxing   If an Integer variable referencing null is unboxed  explicitly or implicitly  a NullPointerException is thrown

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have you ever programmed before then  int  is one of the primitive types you can set for your variables  just like char  float         but Integer is a wrapper class that you can use it to do some functions on an int variable  e g convert it to string or vise versa        but keep note that methods in the wrapper classes are static so you can use them anytime without creating an instance of Integer class  as a recap    int x  Integer y     x and y are both variables of type int but y is wrapped by an Integer class and has several methods that you use but i case you need to call some functions of Integer wrapper class you can do it simply   Integer toString x     but be aware that both x and y are corect but if you want to use them just as a primitive type  use the simple form  used for defining x

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int is predefined in library function c  but in java we can create object of Integer

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Java    int  double  long  byte  float  double  short  boolean  char - primitives  Used for hold the basic data types supported by the language  the primitive types are not part of the object hierarchy  and they do not inherit Object  Thet can be pass by reference to a method    Double  Float  Long  Integer  Short  Byte  Character  and Boolean  are type Wrappers  packaged in java lang  All of the numeric type wrappers define constructors that allow an object to be constructed from a given value  or a string representation of that value  Using objects can add an overhead to even the simplest of calculations    Beginning with JDK 5  Java has included two very helpful features  autoboxing and autounboxing  Autoboxing unboxing greatly simplifies and streamlines code that must convert primitive types into objects  and vice versa     Example of constructors   Integer int num  Integer String str  throws NumberFormatException Double double num  Double String str  throws NumberFormatException   Example of boxing unboxing   class ManualBoxing           public static void main String args              Integer objInt   new Integer 20       Manually box the value 20          int i   objInt intValue        Manually unbox the value 20         System out println i         iOb      displays 20 20           Example of autoboxing autounboxing   class AutoBoxing       public static void main String args              Integer objInt   40     autobox an int         int i   objInt      auto-unbox         System out println i         iOb      displays 40 40           P S  Herbert Schildt s book was taken as a reference

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In C   int is just an alias for System Int32  string for System String  double for System Double etc     Personally I prefer int  string  double  etc  because they don t require a using System  statement    A silly reason  I know

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int is a primitive datatype whereas Integer is an object   Creating an object with Integer will give you access to all the methods that are available in the Integer class   But  if you create a primitive data type with int  you will not be able to use those inbuild methods and you have to define them by yourself  But  if you don t want any other methods and want to make the program more memory efficient  you can go with primitive datatype because creating an object will increase the memory consumption

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This has already been answered for Java  here s the C  answer    Integer  is not a valid type name in C  and  int  is just an alias for System Int32  Also  unlike in Java  or C    there aren t any special primitive types in C   every instance of a type in C   including int  is an object  Here s some demonstrative code   void DoStuff         System Console WriteLine  SomeMethod  int 5         System Console WriteLine  GetTypeName lt int gt          string SomeMethod object someParameter        return string Format  Some text  0    someParameter ToString        string GetTypeName lt T gt          return  typeof  T   FullName

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In Java  the int type is a primitive data type  where as the Integer type is an object   In C   the int type is also a data type same as System Int32  An integer  just like any other value types  can be boxed   wrapped   into an object

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Java Version  In Simple words int is primitive and Integer is wrapper object for int    One example where to use Integer vs int  When you want to compare and int variable again null it will throw error   int a    assuming a value you are getting from data base which is null if a   null     this is wrong - cannot compare primitive to null   do something      Instead you will use  Integer a    assuming a value you are getting from data base which is null if a   null     this is correct legal   do something

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I ll just post here since some of the other posts are slightly inaccurate in relation to C    Correct  int is an alias for System Int32  Wrong  float is not an alias for System Float  but for System Single  Basically  int is a reserved keyword in the C  programming language  and is an alias for the System Int32 value type   float and Float is not the same however  as the right system type for   float   is System Single  There are some types like this that has reserved keywords that doesn t seem to match the type names directly   In C  there is no difference between   int   and   System Int32    or any of the other pairs or keywords system types  except for when defining enums  With enums you can specify the storage size to use and in this case you can only use the reserved keyword  and not the system runtime type name   Wether the value in the int will be stored on the stack  in memory  or as a referenced heap object depends on the context and how you use it   This declaration in a method   int i    defines a variable i of type System Int32  living in a register or on the stack  depending on optimizations  The same declaration in a type  struct or class  defines a member field  The same declaration in a method argument list defines a parameter  with the same storage options as for a local variable   note that this paragraph is not valid if you start pulling iterator methods into the mix  these are different beasts altogether   To get a heap object  you can use boxing   object o   i    this will create a boxed copy of the contents of i on the heap  In IL you can access methods on the heap object directly  but in C  you need to cast it back to an int  which will create another copy  Thus  the object on the heap cannot easily be changed in C  without creating a new boxed copy of a new int value   Ugh  this paragraph doesn t read all that easily

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In java as per my knowledge if you learner then  when you write int a  then in java generic it will compile code like Integer a   new Integer    So as per generics Integer is not used but int is used  so there is so such difference there

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int is a primitive data type  Integer is a wrapper class  It can store int data as objects

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Well  in Java an int is a primitive while an Integer is an Object  Meaning  if you made a new Integer   Integer i   new Integer 6     You could call some method on i   String s   i toString     sets s the string representation of i   Whereas with an int   int i   6    You cannot call any methods on it  because it is simply a primitive  So   String s   i toString     will not work      would produce an error  because int is not an object   int is one of the few primitives in Java  along with char and some others   I m not 100  sure  but I m thinking that the Integer object more or less just has an int property and a whole bunch of methods to interact with that property  like the toString   method for example   So Integer is a fancy way to work with an int  Just as perhaps String is a fancy way to work with a group of chars    I know that Java isn t C  but since I ve never programmed in C this is the closest I could come to the answer  Hope this helps   Integer object javadoc  Integer Ojbect vs  int primitive comparison

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In Java int is a primitive data type while Integer is a Helper class  it is use to convert for one data type to other    For example    double doubleValue   156 5d  Double doubleObject    new Double doubleValue   Byte myByteValue   doubleObject byteValue     String myStringValue   doubleObject toString      Primitive data types are store the fastest available memory where the Helper class is complex and store in heep memory    reference from  David Gassner  Java Essential Training

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In Java there are two basic types in the JVM  1  Primitive types and 2  Reference Types  int is a primitive type and Integer is a class type  which is kind of reference type    Primitive values do not share state with other primitive values  A variable whose type is a primitive type always holds a primitive value of that type   int aNumber   4  int anotherNum   aNumber  aNumber    6  System out println anotherNum      Prints 4   An object is a dynamically created class instance or an array  The reference values  often just references  are pointers to these objects and a special null reference  which refers to no object  There may be many references to the same object   Integer aNumber   Integer valueOf 4   Integer anotherNumber   aNumber     anotherNumber references the                                      same object as aNumber   Also in Java everything is passed by value  With objects the value that is passed is the reference to the object  So another difference between int and Integer in java is how they are passed in method calls  For example in  public int add int a  int b        return a   b    final int two   2  int sum   add 1  two     The variable two is passed as the primitive integer type 2  Whereas in  public int add Integer a  Integer b        return a intValue     b intValue      final Integer two   Integer valueOf 2   int sum   add Integer valueOf 1   two     The variable two is passed as a reference to an object that holds the integer value 2      WolfmanDragon  Pass by reference would work like so   public void increment int x      x   x   1    int a   1  increment a      a is now 2   When increment is called it passes a reference  pointer  to variable a  And the increment function directly modifies variable a   And for object types it would work as follows   public void increment Integer x      x   Integer valueOf x intValue     1     Integer a   Integer valueOf 1   increment a      a is now 2   Do you see the difference now

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int is used to declare primitive variable   e g  int i 10    Integer is used to create reference variable of class Integer  Integer a   new Integer

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In platforms like Java  ints are primitives while Integer is an object which holds a integer field  The important distinction is that primitives are always passed around by value and by definition are immutable    Any operation involving a primitive variable always returns a new value  On the other hand  objects are passed around by reference  One could argue that the point to the object  AKA the reference  is also being passed around by value  but the contents are not

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int  is primitive data-type and  Integer  in Wrapper Class in Java   Integer  can be used as an argument to a method which requires an object  where as  int  can be used as an argument to a method which requires an integer value  that can be used for arithmetic expression

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In Java  the  int  type is a primitive  whereas the  Integer  type is an object   In C   the  int  type is the same as System Int32 and is a value type  ie more like the java  int    An integer  just like any other value types  can be boxed   wrapped   into an object      The differences between objects and primitives are somewhat beyond the scope of this question  but to summarize    Objects provide facilities for polymorphism  are passed by reference  or more accurately have references passed by value   and are allocated from the heap  Conversely  primitives are immutable types that are passed by value and are often allocated from the stack

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There are many reasons to use wrapper classes    We get extra behavior  for instance we can use methods  We can store null values whereas in primitives we cannot Collections support storing objects and not primitives

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