java中Object类4种方法详细介绍

//新建一个HashTest类
public class HashTest {
}

//测试类
public class TestMain {
    public static void main(String[] args) {
        HashTest h = new HashTest();      
        
        int hash = h.hashCode();   //调用hashCode()方法
        System.out.println(hash);  //输出可以得到一串整数
    }
}
//460141958
//这个数也就是哈希码，也称为散列码，
//作用是确定该对象在哈希表中的索引位置

public class HashTest {
}  //还是使用那个类

public class TestMain {
    public static void main(String[] args) {
        HashTest h1 = new HashTest();
        HashTest h2 = new HashTest();  //用一个类去创建两个对象，判断是否相等

        System.out.println(h1.equals(h2));  //语法：h1.equals(h2)
    }
}

//结果：false

//equals源码
   public boolean equals(Object obj) {
        return (this == obj);
    }

public class HashTest {

    private int age;

    public HashTest() {
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

//重写equals方法，只要HashTest生成的对象，传入age参数相等，即可判断两者一致
//重写后的equals，就不在是去判断两者的地址是否相同 
    @Override
    public boolean equals(Object obj){
        HashTest h = (HashTest) obj;    //多态
        if(this.age == h.getAge()) {
            return true;
        }
        return false;
    }
}

//测试类：
public class TestMain {
    public static void main(String[] args) {
        HashTest h1 = new HashTest(5);
        HashTest h2 = new HashTest(5);

        System.out.println(h1.equals(h2));
    }
}

//结果：true

//若吧其中一个age改成6：
public class TestMain {
    public static void main(String[] args) {
        HashTest h1 = new HashTest(5);
        HashTest h2 = new HashTest(6);

        System.out.println(h1.equals(h2));
    }
}
//结果：flase

public class HashTest {
}

//测试类
public class TestMain {
    public static void main(String[] args) {
        HashTest h1 = new HashTest();

        System.out.println(h1.getClass());  //调用getClass()
    }
}

输出值：class HashTest

//在polymorphismTest包下创建了Person类，作为父类
package polymorphismTest;
public class Person {
    public void eat(){
        System.out.println("我会吃饭");
    }
}


//创建Student类，继承Person
package polymorphismTest;
public class Student extends Person{

    @Override    //重写父类eat方法
    public void eat(){
        System.out.println("我是学生，我也还吃饭");
    }
}


//测试类
package polymorphismTest;
public class TestMain {
    public static void main(String[] args) {

        Person p = new Student();    //使用多态
        p.eat();                     //这里其实就是使用了Student子类的方法
        System.out.println(p.getClass());  //查看p到底是什么类
    }
}

//输出结果：
//我是学生，我也还吃饭
//class polymorphismTest.Student

package polymorphismTest;

public class TestMain {
    public static void main(String[] args) {
    
        Person p = new Person();  //当这里不使用多态，而是使用本身的时候
        p.eat();
        System.out.println(p.getClass());
    }
}

//我会吃饭
//class polymorphismTest.Person
//这里返回的就是Person类了

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

public class TestMain {
    public static void main(String[] args) {

        Person p = new Person();
        System.out.println(p.toString());
    }
}
//结果：polymorphismTest.Person@1b6d3586