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

*/