Why is 128==128 false but 127==127 is true when comparing Integer wrappers in Java?

Question

class D {
    public static void main(String args[]) {
        Integer b2=128;
        Integer b3=128;
        System.out.println(b2==b3);
    }
}

Answer 1

It is memory optimization in Java related.

To save on memory, Java 'reuses' all the wrapper objects whose values fall in the following ranges:

All Boolean values (true and false)

All Byte values

All Character values from \u0000 to \u007f (i.e. 0 to 127 in decimal)

All Short and Integer values from -128 to 127.