Java深入讲解Object类常用方法的使用

//实例1：使用类和字符串两种对象比较运算符"=="和equals()方法的不同
//filename:A_2.java
class A{
    int a=1;
}
public class A_2{
    public static void main(String[] args){
    	  A obj1=new A();
    	  A obj2=new A();
        String s1,s2,s3="abcd",s4="abcd";
        s1=new String("abcd");
        s2=new String("abcd");
        System.out.println("s1.equals(s2)是"+(s1.equals(s2)));//true
        System.out.println("s1==s2是"+(s1==s2));//false
        System.out.println("s1.equals(s3)是"+(s1.equals(s3)));//true
        System.out.println("s1==s2是"+(s1==s2));//false
        System.out.println("s3.equals(s4)是"+(s3.equals(s4)));//true
        System.out.println("s3==s4是"+(s3==s4));//true
        System.out.println("obj1==obj2是"+(obj1==obj2));//false
        System.out.println("obj1.equals(obj2)是"+(obj1.equals(obj2)));//false
        obj1=obj2;
        System.out.println("obj1=obj2后obj1==obj2是"+(obj1==obj2));//true
        System.out.println("obj1=obj2后obj1.equals(obj2)是"+(obj1.equals(obj2)));//true
    }
}
/**
s1.equals(s2)是true
s1==s2是false
s1.equals(s3)是true
s1==s2是false
s3.equals(s4)是true
s3==s4是true
obj1==obj2是false
obj1.equals(obj2)是false
obj1=obj2后obj1==obj2是true
obj1=obj2后obj1.equals(obj2)是true
*/

//实例2:对象运算符instanceof，getName(),getSuperclass()方法：
//filename:Person.java
import java.io.*;
public class Person{
    static int count=0;//定义静态变量
    protected String name;
    protected int age;
    public Person(String name,int age){
        this.name=name;
        this.age=age;
        this.count++;
    }
    public String toString(){
        return this.name+","+this.age;
    }
    public void display(){
        System.out.println("本类名="+this.getClass().getName()+";");
        System.out.println("父类名="+this.getClass().getSuperclass().getName()+";");
        System.out.println("Person.count="+this.count+" ");
        System.out.println("Student.count="+Student.count+" ");
        Object obj=this;
        if(obj instanceof Student)
            System.out.println(obj.toString()+"是Student类对象");
        if(obj instanceof Person)
            System.out.println(obj.toString()+"是Person类对象");
    }
     public static void main(String[] args){
        Person per=new Person("张三",18);
        per.display();
        Student stu=new Student("李四",19,"计算机");
        stu.display();
    }

}
class Student extends Person{
    static int count=0;//隐藏父类的count
    protected String dept;
    protected Student(String n1,int a1,String d1){
        super(n1,a1);
        dept=d1;
        this.count++;
    }
    public String toString(){
        return super.toString()+","+dept;
    }
    public void display(){
        super.display();
        System.out.println("super.count="+super.count+" ");//引用父类的变量
        System.out.println("this.count="+this.count+" ");
    }
   
}
/**
本类名=Person;
父类名=java.lang.Object;
Person.count=1
Student.count=0
张三,18是Person类对象
本类名=Student;
父类名=Person;
Person.count=2
Student.count=1
李四,19,计算机是Student类对象
李四,19,计算机是Person类对象
super.count=2
this.count=1
*/