java == operator

Possible Duplicate:
Weird Java Boxing

Hi,

Can somebody explain why the last print returns false ?

int a = 100;
int b = 100;

System.out.println(a == b); // prints true

Integer aa = 100;
Integer bb = 100;

System.out.println(aa == bb); // prints true

Integer aaa = 1000;
Integer bbb = 1000;

System.out.println(aaa == bbb); // prints false

Thanks Michael