Question

can Any body explain me what is happeing in the output.
If == is use to compare two ref. variable it simply check its reference if they are same then it enter in if body, then why the hell
aa==bb is equal if creting static method valueOf() and ee==ff is not equal (which is ok) if creating its object using new keyword ?

static void main(String args[])
{
    Integer aa = Integer.valueOf("12");
    Integer bb = Integer.valueOf("12");
    if(aa==bb)System.out.println("aa==bb");
    if(aa!=bb)System.out.println("aa!=bb");
    Integer ee = new Integer("12");
    Integer ff = new Integer("12");


    if(ee==ff)System.out.println("ee==ff");
    if(ee!=ff)System.out.println("ee!=ff");
}

Output :

aa==bb

ee!=ff

Answer 1

The == comparator checks for object equality!

Since Integer.valueOf maintains a cache of Integer Objects with the value -128 to 127 valueOf(String) returns the cached object, thus the == comparance results in true.

Integer a1 = new Integer("12");
Integer b1 = new Integer("12");
//a1 == b1 returns false because they point to two different Integer objects

Integer aa = Integer.valueOf("12");
Integer bb = Integer.valueOf("12");
//aa == bb returns true because they point to same cached object

For the comparance of object values always use the .equals method, for primitives like int, long etc. you can use the == comparator.