java – 整数类对象

参见英文答案 > Weird Integer boxing in Java????????????????????????????????????10个
我有一个代码片段：

public class Test{
    public static void main(String args[]){
        Integer a = 100;
        Integer b = 100;
        Integer c = 5000;
        Integer d = 5000;

        System.out.println(a);
        System.out.println(b);
        System.out.println(c);
        System.out.println(d);
        if(a == b)
            System.out.println("a & b Both are Equal");
        else
            System.out.println("a & b are Not Equal");
        if(c == d)
            System.out.println("c & d Both are Equal");
        else
            System.out.println("c & d are Not Equal");
    }
}

我不明白为什么输出是这样的？
输出是：
a& b两者是平等的
c& d不相等
我正在使用jdk1.7