Question

Say we have two Integer objects:

Integer i=100,j=200;

Does (j-i) evaluate to another Integer Wrapper object with value 100, or a primitive int?

Answer 1

Quick test shows that java is using an Integer cache, and re-uses the i:

@Test
public void test() {
    Integer i=100, j=200;
    System.out.println("i: " + System.identityHashCode(i));
    System.out.println("j: " + System.identityHashCode(j));

    Integer sub = j-i;
    System.out.println("j-i: " + System.identityHashCode(sub));
}

Outputs:

i: 1494824825
j: 109647522
j-i: 1494824825 <-- same as i