Object類別之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); //false   
        System.out.println(c1.equals(c2)); //false   
        String s1 = new String("hello");    
        String s2 = new String("hello");   
        String m1 = "hello";   
        String m2 = "hello";   
        System.out.println(s1 == s2); //false   
        System.out.println(m1 == m2); //true   
        System.out.println(s1.equals(s2));  //true   
    }   
}   
//实体类   
class Cat {   
    int color;   
    int height, weight;   
       
    public Cat(int color, int height, int weight) {   
        this.color = color;   
        this.height = height;   
        this.weight = weight;   
    }   
    //重写equals方法   
    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;   
    }   
}