JAVA中，instanceof的讲解

一 instanceof是java中的一个二元操作符。
二 instanceof的作用是测试它左边的对象是否是它右边类的实例，返回的是boolean类型的数据。他是判断对象是属于哪个类别的

举个例子
String st=”China”;
boolean judge=s instanceof st;
//此时judge的值为true 因为，st是Object类的一个实例

下面我们看一下关于instanceof的java程序：
有三个文件Phone.java,Apple.java,Instanceof.java

Phone.java

public class Phone {    public Phone(String num)    {        this.num=num;    }    public void setNum(String num)    {        this.num=num;    }    public String getNum(String num)    {        return num;    }    private String num;}

Apple.java

public class Apple extends Phone{    public Apple(String num,double price)    {        super(num);        // TODO Auto-generated constructor stub        this.price=price;    }    public void setPrice(double price)    {        this.price=price;    }    public double getPrice()    {        return price;    }    public void gongneng()    {        System.out.println("苹果手机具有指纹功能");    }    private double price;}

Instanceof2.java

public class Instanceof2 {    public static void main(String[] args)    {        int i=100;        int j=100;        String s1="一一一";        String s2="一一一";        String s3=new String("一一一");        String s4=new String("一一一");        Phone p1=new Phone("0001");        Phone p2=new Phone("0001");        Phone p3=p1;        Apple a=new Apple("0001",5000);        System.out.println("基本的类型比较如下:  ");        System.out.print("i和j的比较: ");        System.out.println(i==j);        System.out.println("String的比较: ");        System.out.println("s1和s2的比较: ");        System.out.println("s1==s2: "+(s1==s2));        System.out.println("s1.equals(s2):" +(s1.equals(s2)));        System.out.println("s1==s3: "+(s1==s3));        System.out.println("s1.equals(s3): "+(s1.equals(s3)));        System.out.println("s3.equals(s4): "+(s3.equals(s4)));        System.out.println();        System.out.println("使用instanceof来比较");        System.out.println(a instanceof Phone);        if(a instanceof Apple)        {            a.gongneng();        }        else        {            System.out.println(a instanceof Apple);         };        System.out.println(p1 instanceof Phone);        System.out.println(p1 instanceof Apple);        System.out.println();        System.out.println("对象之间的比较: ");        System.out.println(p1==p3);        System.out.println(p1.equals(p3));        System.out.println(p1.equals(p2));        System.out.println(p1.hashCode()==p2.hashCode());        System.out.println(p1==p2);    }}