第五章：多态、笔记

父类：

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

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

子类一：

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：

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，子类的扩展的独有方法无法调用

public class Demo {
    public static void main(String[] args) {
    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
判断对象是否是给定的类的实例

作用：避免类型转换时，出现错误，进而引发程序的崩溃

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();
        }
    }
}

第五章：多态 、笔记

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第五章：多态、笔记