JAVA基础--toString, equals方法

==比较的是地址

equals比较的是内容.

所以要重写object的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, 3);
		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;
	}

}

结果:

--------------------Configuration: <Default>--------------------
false
true
false
true

　

如果直接输出一个对象, 会输出类名字@hashcode,

应该重写toString方法:

public class TestToString {
	public static void main(String[] args) {
		Dog d = new Dog();
		System.out.println("d:=" + d);
	}
}

class Dog {
	public String toString() {
		return "I'm a cool dog!";
	}
}