Java == strange behavior

Question

I wanted to check Integer equality in my application but came across a strange behavior. At some point my application was working correctly but at some point it was failing. So I just written a test code over here

public class EqualityTest {

     public static void main(String args[]) {
           Integer a = 100;
           Integer b = 100;
           Integer c = 1000;
           Integer d = 1000;
           if (a == b) {
                 System.out.println("a & b are Equal");
           }
           else {
                 System.out.println("a & b are Not Equal");
           }

           if (c == d) {
                 System.out.println("c & d are Equal");
           } else {
                 System.out.println("c & d are Not Equal");
           }
     }
}

Output

a & b are Equal
c & d are Not Equal

here my question is why c and d are not equal?

check: http://stackoverflow.com/questions/3131136/integers-caching-in-java — Paweł Adamski, Jan 21 '14 at 06:42
also related answer from [this](http://stackoverflow.com/a/20877115/2817802) — Baby, Jan 21 '14 at 06:50
Refer java docs. http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html. public static Integer valueOf(int i) its since 1.5 — Vinayak Pingale, Jan 21 '14 at 06:51

score 6 · Answer 1 · answered Jan 21 '14 at 06:44

6

Integer uses caching of small values in range of -128 to 127, and so you get same instance for small values such as 100.

For the values outside this range, a new Integer instance is created and returned.

answered Jan 21 '14 at 06:44

Narendra Pathai

41,187
18
82
120

and the cached value is between -128 to 127.. Anything within this range, you get the same object (so 100 gives equal.) and anything outside this range, a new object is returned (2 new Integer objects with value 1000 .. So you get false..) – TheLostMind Jan 21 '14 at 06:46

score 3 · Answer 2 · answered Jan 21 '14 at 06:47

Integer is mutable class and keep around -128 to 127 integers in cache. So == will work on Integers -128 <= i <= 127

Each time you create Integer with this range it will return you the same object previously created.

For Java 7 implementation could be achieved with system property:

-Djava.lang.Integer.IntegerCache.high=<size>

score -3 · Answer 3 · answered Jan 21 '14 at 06:42

-3

Integer is an Object. You should use equal instead of == like

if(a.equal(b)){
...
}

answered Jan 21 '14 at 06:42

Ryker.Wang

757
1
9
18

Doesnt answer the question.. OP already knows this... – TheLostMind Jan 21 '14 at 06:45
this is not in the complete answer: please address caching of small values. – ljgw Jan 21 '14 at 06:46

score -4 · Answer 4 · answered Jan 21 '14 at 06:43

        Integer a = 100;
        Integer b = 100;
        Integer c = 1000;
        Integer d = 1000;
        if (a.equals(b)) {
            System.out.println("a & b are Equal");
        }
        else {
            System.out.println("a & b are Not Equal");
        }
        if (c.equals(d)) {
            System.out.println("c & d are Equal");
        } else {
            System.out.println("c & d are Not Equal");
        }

==means their pointer or reference equal,not value equal.You should call .equals method

this is not in the complete answer: please address caching of small values. — ljgw, Jan 21 '14 at 06:45

Java == strange behavior

4 Answers4