java自动拆箱和装箱问题，相等判断问题

Question

public static void main(String[] args) {
        Integer a = 1;
        Integer b = 2;
        Integer c = 3;
        Integer d = 3;
        Integer e = 321;
        Integer f = 321;
        int ee = 321;
        int ff = 321;
        Long g = 3L;
        System.out.println(c==d);
        System.out.println(e==f);
        System.out.println(ee==ff);
        System.out.println(c==(a+b));
        System.out.println(c.equals(a+b));
        System.out.println(g==(a+b));
        System.out.println(g.equals(a+b));
    }

结果：
true
false
true
true
true
true
false

 为什么会产生这样的结果呢，c、d相等，e、f不等这是为什么