Java中Integer和int的使用及注意点

    public static void main(String[] args) {
        // Integer和Long都是缓存在-128~127之间，所以可以直接比较，不用equals
        Integer i1 = 127;
        Integer i2 = 127;
        System.out.println(i1 == i2);
        System.out.println(i1.equals(i2));
        System.out.println("=====");
        Integer i3 = 128;
        Integer i4 = 128;
        System.out.println(i3 == i4);
        System.out.println(i3.equals(i4));
        System.out.println("=====");

        Long ii1 = 127L;
        Long ii2 = 127L;
        Long ii3 = 128L;
        Long ii4 = 128L;
        System.out.println(ii1 == ii2);
        System.out.println(ii3 == ii4);
        System.out.println(ii1.equals(ii2));
        System.out.println(ii3.equals(ii4));
    }

	private final int value;
    public boolean equals(Object obj) {
        if (obj instanceof Integer) {
            return value == ((Integer)obj).intValue();
        }
        return false;
    }

    public static void main(String[] args) {
        // 由于int类型是基本数据类型，拆箱时不能为空
        // 例1
        Integer i5 = null;
        System.out.println(i5 == 3);
    }

    public static void main(String[] args) {
        // 由于int类型是基本数据类型，拆箱时不能为空
        // 例2
        Integer i5 = null;
        test1(i5);
    }

    public static void test1(int i) {
        System.out.println(i);
    }