Java.lang.Integer behaviour

Question

Hi all,
While preparing for my SCJP6 i was playing with the java.lang.Integer integer wrapper. I found some behaviour which I could not explain. Below is the code and output on jre6.
public void test(){
          Integer int1 = 100;
          Integer int2 = 100;
          System.out.println(int1!=int2);
          System.out.println(int1==int2);
          System.out.println(int1.equals(int2));
     }OUTPUT:
false
true
true
     public void test(){
          Integer int1 = 1000;
          Integer int2 = 1000;
          System.out.println(int1!=int2);
          System.out.println(int1==int2);
          System.out.println(int1.equals(int2));
     }OUTPUT:
true
false
true
As you can see the == and != operators behave differently for values 100 and 1000.
Please let me know why is it so.
Thanks.

Answer 1

Thanks for the post,
again i'd stress on the fact that I want to be able to determine the behavior of == and != operator regardless of whether i should use them or not.
Some place i have read that == actually Unboxes the object and compares the values and not the Object ref where as != always compares the obj ref only.
The behavior i have found is that both operators work on the actual object reference. If the Object value is >-129 and <128 then the JVM uses the same underlying object(cached one) and if the value is out of this range then new object is created.
So
Integer i=1000,i2=1000;
i==i2 OUTPUT false
i!=i2 OUTPUT true.
Integer i=100,i2=100;
i==i2 OUTPUT true
i!=i2 OUTPUT false.
I just want a web link where I can confirm my findings.
Edited by: rishabhchandra on Jun 20, 2009 7:30 PM