Behavior of Integer Wrapper class and operator

Question

I have the below code:

Integer integer1 = 127;
Integer integer2 = 127;
System.out.println(integer1 == integer2);//true

integer1 = 128;
integer2 = 128;
System.out.println(integer1 == integer2);//false

When I am executing this, my == operator is working fine for -128 to 127 else its returning me false. Can someone explain why so?

Answer 1

Well, this is happening because of the below code of Integer wrapper class:

public static Integer valueOf(int i) {
    if(i >= -128 && i <= IntegerCache.high)
        return IntegerCache.cache[i + 128];
    else
        return new Integer(i);
}

To put it in simple words, when you write,

Integer integer1 = 127;

It means,

Integer integer1 = Integer.valueOf(127);

Thus, for values between -128 to 127, the Integers are kept in cache and are returned multiple times from there whereas, for values lower than -128 or higher than 127, new Integers are generated.