How to properly compare two Integers in Java

Question

I know that if you compare a boxed primitive Integer with a constant such as   Integer a   4  if  a  lt  5    a will automatically be unboxed and the comparison will work   However  what happens when you are comparing two boxed Integers and want to compare either equality or less than greater than   Integer a   4  Integer b   5   if  a    b    Will above code result in checking to see if they are the same object  or will it auto-unbox in that case   What about   Integer a   4  Integer b   5   if  a  lt  b

User · Answer

Because comparaison method have to be done based on type int  x  y  or class Integer  x equals y    with right operator  public class Example        public static void main String   args         int   arr    -32735  -32735  -32700  -32645  -32645  -32560  -32560            for int j 1  j lt arr length-1  j                if  arr j-1   arr j    amp  amp   arr j   arr j 1                     System out println  int gt   arr j          Integer   I arr    -32735  -32735  -32700  -32645  -32645  -32560  -32560            for int j 1  j lt I arr length-1  j                if   I arr j-1  equals I arr j     amp  amp    I arr j  equals I arr j 1                      System out println  Interger gt   I arr j

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Since Java 1 7 you can use Objects equals   java util Objects equals oneInteger  anotherInteger        Returns true if the arguments are equal to each other and false   otherwise  Consequently  if both arguments are null  true is returned   and if exactly one argument is null  false is returned  Otherwise    equality is determined by using the equals method of the first   argument

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checks for reference equality  however when writing code like   Integer a   1  Integer b   1    Java is smart enough to reuse the same immutable for a and b  so this is true  a    b   Curious  I wrote a small example to show where java stops optimizing in this way   public class BoxingLol       public static void main String   args            for  int i   0  i  lt  Integer MAX VALUE  i                  Integer a   i              Integer b   i              if  a    b                    System out println  Done      i                   System exit 0                                   System out println  Done  all values equal              When I compile and run this  on my machine   I get   Done  128

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will still test object equality   It is easy to be fooled  however   Integer a   10  Integer b   10   System out println a    b     prints true  Integer c   new Integer 10   Integer d   new Integer 10    System out println c    d     prints false   Your examples with inequalities will work since they are not defined on Objects   However  with the    comparison  object equality will still be checked   In this case  when you initialize the objects from a boxed primitive  the same object is used  for both a and b    This is an okay optimization since the primitive box classes are immutable

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We should always go for equals   method for comparison for two integers Its the recommended practice   If we compare two integers using     that would work for certain range of integer values  Integer from -128 to 127  due to JVM s internal optimisation   Please see examples   Case 1       Integer a   100     Integer b   100   if  a    b        System out println  a and b are equal      else      System out println  a and b are not equal         In above case JVM uses value of a and b from cached pool and return the same object instance therefore memory address  of integer object and we get both are equal Its an optimisation JVM does for certain range values   Case 2  In this case  a and b are not equal because it does not come with the range from -128 to 127      Integer a   220     Integer b   220   if  a    b        System out println  a and b are equal      else      System out println  a and b are not equal         Proper way   Integer a   200               Integer b   200    System out println  a    b      a equals b       true   I hope this helps

User · Answer

No     between Integer  Long etc will check for reference equality - i e   Integer x        Integer y         System out println x    y     this will check whether x and y refer to the same object rather than equal objects   So  Integer x   new Integer 10   Integer y   new Integer 10    System out println x    y     is guaranteed to print false  Interning of  small  autoboxed values can lead to tricky results   Integer x   10  Integer y   10   System out println x    y     This will print true  due to the rules of boxing  JLS section 5 1 7   It s still reference equality being used  but the references genuinely are equal      If the value p being boxed is an integer literal of type int between   -128 and 127 inclusive    3 10 1   or the boolean literal true or false    3 10 3   or a character literal between   u0000  and   u007f    inclusive    3 10 4   then let a and b be the results of any two boxing   conversions of p  It is always the case that a    b    Personally I d use   if  x intValue      y intValue      or  if  x equals y     As you say  for any comparison between a wrapper type  Integer  Long etc  and a numeric type  int  long etc  the wrapper type value is unboxed and the test is applied to the primitive values involved   This occurs as part of binary numeric promotion  JLS section 5 6 2   Look at each individual operator s documentation to see whether it s applied  For example  from the docs for    and     JLS 15 21 1       If the operands of an equality   operator are both of numeric type  or   one is of numeric type and the other   is convertible    5 1 8  to numeric   type  binary numeric promotion is   performed on the operands    5 6 2     and for  lt    lt     gt  and  gt    JLS 15 20 1      The type of each of the operands of a   numerical comparison operator must be   a type that is convertible    5 1 8  to   a primitive numeric type  or a   compile-time error occurs  Binary   numeric promotion is performed on the   operands    5 6 2   If the promoted   type of the operands is int or long    then signed integer comparison is   performed  if this promoted type is   float or double  then floating-point   comparison is performed    Note how none of this is considered as part of the situation where neither type is a numeric type

User · Answer

Calling  if  a    b    Will work most of the time  but it s not guaranteed to always work  so do not use it   The most proper way to compare two Integer classes for equality  assuming they are named  a  and  b  is to call   if a    null  amp  amp  a equals b       System out println  They are equal        You can also use this way which is slightly faster      if a    null  amp  amp  b    null  amp  amp   a intValue      b intValue             System out println  They are equal             On my machine 99 billion operations took 47 seconds using the first method  and 46 seconds using the second method  You would need to be comparing billions of values to see any difference   Note that  a  may be null since it s an Object  Comparing in this way will not cause a null pointer exception   For comparing greater and less than  use  if  a    null  amp  amp  b  null        int compareValue   a compareTo b       if  compareValue  gt  0            System out println  a is greater than b          else if  compareValue  lt  0            System out println  b is greater than a          else               System out println  a and b are equal            else       System out println  a or b is null  cannot compare

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this method compares two Integer with null check  see tests  public static boolean compare Integer int1  Integer int2        if int1  null            return int1 equals int2         else           return int2  null              inline version        return  int1  null    int1 equals int2    int2  null       results  System out println compare 1 1                true System out println compare 0 1                false System out println compare 1 0                false System out println compare null 0             false System out println compare 0 null             false System out println compare null null          true

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In my case I had to compare two Integers for equality where both of them could be null  Searched similar topic  didn t found anything elegant for this  Came up with a simple utility functions   public static boolean integersEqual Integer i1  Integer i2        if  i1    null  amp  amp  i2    null            return true            if  i1    null  amp  amp  i2    null            return false            if  i1    null  amp  amp  i2    null            return false            return i1 intValue      i2 intValue         considering null is less than not-null public static int integersCompare Integer i1  Integer i2        if  i1    null  amp  amp  i2    null            return 0            if  i1    null  amp  amp  i2    null            return -1            return i1 compareTo i2

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tl dr my opinion is to use a unary   to trigger the unboxing on one of the operands when checking for value equality  and simply use the maths operators otherwise  Rationale follows   It has been mentioned already that    comparison for Integer is identity comparison  which is usually not what a programmer want  and that the aim is to do value comparison  still  I ve done a little science about how to do that comparison most efficiently  both in term of code compactness  correctness and speed   I used the usual bunch of methods   public boolean method1         Integer i1   7  i2   5      return i1 equals  i2       public boolean method2         Integer i1   7  i2   5      return i1 intValue      i2 intValue       public boolean method3         Integer i1   7  i2   5      return i1 intValue      i2     public boolean method4         Integer i1   7  i2   5      return i1     i2     public boolean method5        obviously not what we want       Integer i1   7  i2   5      return i1    i2      and got this code after compilation and decompilation   public boolean method1         Integer var1   Integer valueOf  7        Integer var2   Integer valueOf  5         return var1 equals  var2       public boolean method2         Integer var1   Integer valueOf  7        Integer var2   Integer valueOf  5         if   var2 intValue      var1 intValue               return true        else           return false           public boolean method3         Integer var1   Integer valueOf  7        Integer var2   Integer valueOf  5         if   var2 intValue      var1 intValue               return true        else           return false           public boolean method4         Integer var1   Integer valueOf  7        Integer var2   Integer valueOf  5         if   var2 intValue      var1 intValue               return true        else           return false           public boolean method5         Integer var1   Integer valueOf  7        Integer var2   Integer valueOf  5         if   var2    var1             return true        else           return false            As you can easily see  method 1 calls Integer equals    obviously   methods 2-4 result in exactly the same code  unwrapping the values by means of  intValue   and then comparing them directly  and method 5 just triggers an identity comparison  being the incorrect way to compare values   Since  as already mentioned by e g  JS  equals   incurs an overhead  it has to do instanceof and an unchecked cast   methods 2-4 will work with exactly the same speed  noticingly better than method 1 when used in tight loops  since HotSpot is not likely to optimize out the casts  amp  instanceof   It s quite similar with other comparison operators  e g   lt   gt   - they will trigger unboxing  while using compareTo   won t - but this time  the operation is highly optimizable by HS since intValue   is just a getter method  prime candidate to being optimized out    In my opinion  the seldom used version 4 is the most concise way - every seasoned C Java developer knows that unary plus is in most cases equal to cast to int  intValue   - while it may be a little WTF moment for some  mostly those who didn t use unary plus in their lifetime   it arguably shows the intent most clearly and most tersely - it shows that we want an int value of one of the operands  forcing the other value to unbox as well  It is also unarguably most similar to the regular i1    i2 comparison used for primitive int values   My vote goes for i1     i2  amp  i1  gt  i2 style for Integer objects  both for performance  amp  consistency reasons  It also makes the code portable to primitives without changing anything other than the type declaration  Using named methods seems like introducing semantic noise to me  similar to the much-criticized bigInt add 10  multiply -3  style

[java] How to properly compare two Integers in Java?

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