Object

Object所有类的根类

常用的共性

equals hashCode toString getClass 都可以覆写自定义

equals 判断两个对象是否相等

Person p1 = new Person();
Person p2 = new Person();
Person p3 = p1;

System.out.print(p1==p2) //false
System.out.print(p1.equals(p2)) //false
System.out.print(p1.equals(p3)) //true

每个类都可以覆盖equals，定义自己的逻辑

public class TestObject extends Object {

	int id;
	String name;
	
	public TestObject(int id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		TestObject other = (TestObject) obj;
		if (id != other.id)
			return false;
		return true;
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TestObject object1 = new TestObject(1000,"旺财");
		TestObject object2 = new TestObject(1000, "小强");
		System.out.println(object1==object2);
		System.out.println(object1.equals(object2));
		
		String string = "123";
		System.out.println(string.equals("123"));
		
	}
	
}

hasCode 类的哈希值

//覆盖hasCode函数
public int hasCode(){
    return age;
}

public class Object_demo1 {
    private int age;

    public Object_demo1(int age) {
        this.age = age;
    }

    public boolean equals(Object o){
        Object_demo1 od = (Object_demo1)o;
        return this.age == od.age;
    }
    public int hashCode(){
        return this.age;
    }
}

Object_demo1 od = new Object_demo1(20);
Object_demo1 od1 = new Object_demo1(20);
System.out.println(od.equals(od1));
System.out.println(od.hasCode());


System.out.println(od);
System.out.println(od.hashCode());
System.out.println(Integer.toHexString(od.hashCode()));

//未覆盖hashCode
//com.company.Object_demo1@2cfb4a64
//754666084
//2cfb4a64

//已覆盖hashCode
//com.company.Object_demo1@14
//20
//14

toString

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

getClass

System.out.println(od.getClass() == od1.getClass()); //true
System.out.println(od.getClass().getName()); 
//com.company.Object_demo1