java 拆箱装箱

public class Test1 {
    public static void main(String[] args) {
        int a = 3;
        Integer a1 = new Integer(a);
        Integer a2 = Integer.valueOf(a);    // converting int into Integer
        Integer a3 = a; //autoboxing, now compiler will write Integer.valueOf(a) internally

        System.out.println(a1 instanceof Integer);
        System.out.println(a2 instanceof Integer);
        System.out.println(a3 instanceof Integer);

        int a4 = a1.intValue(); // converting Integer to int
        int a5 = a1;    // unboxing, now compiler will write a.intValue() internally

    }
}