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();
}
}
}
