Object类之equals方法

public class TestEquals {
    public static void main(String[] args) {
        Cat c1 = new Cat(1, 2, 3);
        Cat c2 = new Cat(1, 2, 6);
        System.out.println(c1 == c2);
        System.out.println(c1.equals(c2));
        
        String s1 = new String("hello");
        String s2 = new String("hello");
        System.out.println(s1 == s2);
        System.out.println(s1.equals(s2)); 
    }
}

class Cat {
    int color;
    int height, weight;
    
    public Cat(int color, int height, int weight) {
        this.color = color;
        this.height = height;
        this.weight = weight;
    }
    
    public boolean equals(Object obj) {
        if(obj == null) return false;
        else {
            if(obj instanceof Cat) {
                Cat c = (Cat)obj;
                if(c.color == this.color && c.height == this.height && c.weight == this.weight) {
                    return true;
                }
            }
        }
        
        return false;
    }
    
}