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Unexpected result when comparing ints

Possible duplicate:
Integer shell objects use the same instances only within 127?
How do operators work? = and == for integers in Java?

I tried to compare two ints with the following cases and got unexpected results

  • when I did the following, @@@ was printed.

     class C {
   static Integer a = 127;
   static Integer b = 127;
   public static void main(String args[]){
   if(a==b){
      System.out.println("@@@"); 
   }
   }
 }

  • when I did the following, @@@ was not printed.

     class C {
   static Integer a = 145;
   static Integer b = 145;
   public static void main(String args[]){
   if(a==b){
      System.out.println("@@@"); 
   }
   }
 }

Can anyone tell me what could be the reason.

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4 answers

You are comparing object identifiers. For values ​​below 128, the Integer class caches its objects. That is why in the first example it is equal. Another example is with higher values ​​that are not cached.

@niklon, -128 .

VM arg -Djava.lang.Integer.IntegerCache.high=4711.

: http://vanillajava.blogspot.co.uk/2012/01/surprising-results-of-autoboxing.html

+8

int s, . .equals int Object.

+5

Integer, int. , .equals(...) ==. , ==.

, == , , .

+1

if(a.equals(b)) == , Object.

== , int, long ..

+1

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