@EqualsAndHashCode

官方文档：https://projectlombok.org/features/EqualsAndHashCode

网友文章参考：http://www.pianshen.com/article/1619125852/

不加 @EqualsAndHashCode 时：

public class Apple {
    private String color;

    public Apple(String color) {
        this.color = color;
    }
    
    public static void main(String[] args) {
        Apple a1 = new Apple("green");
        Apple a2 = new Apple("red");
        // hashMap stores apple type and its quantity
        HashMap m = new HashMap();
        m.put(a1, 10);
        m.put(a2, 20);
        System.out.println(m.get(new Apple("green")));     //输出为 null
        System.out.println(m.get(a1));  //输出为 10
    }
}

加 @EqualsAndHashCode 时：

@EqualsAndHashCode
public class Apple {
    private String color;

    public Apple(String color) {
        this.color = color;
    }


    public static void main(String[] args) {
        Apple a1 = new Apple("green");
        Apple a2 = new Apple("red");
        // hashMap stores apple type and its quantity
        HashMap m = new HashMap();
        m.put(a1, 10);
        m.put(a2, 20);
        System.out.println(m.get(new Apple("green")));   //输出为 10
        System.out.println(m.get(a1));   //输出为 10
    }
}