compare two Integer objects with == in java

Question

public class Problem {

    public static void main(String args[]){
        Integer a=200;
        Integer b=200;
        Integer c=20;
        Integer d=20;

        System.out.println(a==b);
        System.out.println(a.equals(b));
        System.out.println(c==d);
        System.out.println(c.equals(d));
    }
}

output

false
true
true
true

TheLostMind · Accepted Answer · 2014-09-18T05:27:54.003

3

Integer class keeps a local cache between -128 to 127 and returns the same object. So,

    Integer a=200; --> Internally converted to Integer.valueOf(200);
    Integer b=200; // not same as a
    Integer c=20;
    Integer d=20; // same as c

    Integer c=new Integer(20);
    Integer d=new Integer(20);
    c==d --> returns false; because you are comparing references.

edited Sep 18 '14 at 05:27

answered Sep 18 '14 at 05:22

TheLostMind

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is it so.did not know about a local cache. seems an awesome answer – vikeng21 Sep 18 '14 at 05:30
@vikeng21 - Yep. That's the case. check [oracle doc](http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#valueOf) – TheLostMind Sep 18 '14 at 05:33

score 1 · Answer 2 · answered Sep 18 '14 at 05:28

Compare objects only using equals except you really want to make sure both are the same objects not just equal. In case of the boxed primitives I believe that I have Seen once that some basic numbers are cached so that in these cases Java will return one and the same object. I can't verify this right now but this would explain the behavior you are facing.

compare two Integer objects with == in java

2 Answers2