FeiGe快递系统--多态

多态

父类

package edu.xcdq;

public class Uncle {
    private String name;
    private int age;

    public void faHongbao() {
        System.out.println("舅舅发红包");
    }
}

子类一：

package edu.xcdq;

public class UncleOne extends Uncle{
    public void faHongbao() {
        System.out.println("大舅不仅发红包，还送烟");
    }
    public void chouyan() {
        System.out.println("大舅喜欢抽烟");
    }
}

子类二：

package edu.xcdq;

public class UncleTwo extends Uncle{
    public void faHongbao() {
        System.out.println("二舅不仅发红包，还送酒");
    }
}

启动类：

多态

public class Demo {
    public static void main(String[] args) {
        //    多态
        Uncle    uncle1 = new UncleOne();
        uncle1.faHongbao();
        Uncle uncle2 = new UncleTwo();  //   向上转型
        uncle2.faHongbao();
         

用父类接受子类的对象，只能调用父类中出现过的方法，子类扩展的独有的方法无法调用

public class Demo {
    public static void main(String[] args) {
        //    多态
        Uncle    uncle1 = new UncleOne();
        //   uncle1.chouyan();   不能调用

向上转型

Uncle uncle2 = new UncleTwo();  //   向上转型
        uncle2.faHongbao();

向下转型

Uncle    uncle1 = new UncleOne();
UncleOne u1 = (UncleOne) uncle1; //   向下转型
        u1.faHongbao();
        u1.chouyan();

instanceof

判断对象是否给定的类的实例

作用：避免类型转换时，出现错误，进而引发程序的崩溃

package edu.xcdq;

public class Demo01 {
    public static void main(String[] args) {
        Uncle uncle1 = new UncleOne();
        if ( uncle1 instanceof  UncleTwo ) {
            UncleTwo u2 = (UncleTwo) uncle1;
            u2.faHongbao();
        }
        if ( uncle1 instanceof UncleOne ) {
            UncleOne u1 = (UncleOne) uncle1;
            u1.faHongbao();
            u1.chouyan();
        }
    }
}