Java学习第9天（5）:面向对象-多态-应用例子

/*需求：电脑运行实例，电脑运行基于主板。*/interface PCI{public void open();public void close();}class MainBoard{public void run(){System.out.println("mainboard run ");}public void usePCI(PCI p)//PCI p = new NetCard()//接口型引用指向自己的子类对象。{if(p!=null){p.open();p.close();}}}class NetCard implements PCI{public void open(){System.out.println("netcard open");}public void close(){System.out.println("netcard close");method();}}class SoundCard implements PCI{public void open(){System.out.println("SoundCard open");}public void close(){System.out.println("SoundCard close");}}/*class MainBoard{public void run(){System.out.println("mainboard run");}public void useNetCard(NetCard c){c.open();c.close();}}class NetCard{public void open(){System.out.println("netcard open");}public void close(){System.out.println("netcard close");}}*/class DuoTaiDemo5 {public static void main(String[] args) {MainBoard mb = new MainBoard();mb.run();mb.usePCI(null);mb.usePCI(new NetCard());mb.usePCI(new SoundCard());}}Java学习第9天（6）:面向对象-多态-object/*Object:是所有对象的直接后者间接父类，传说中的上帝。该类中定义的肯定是所有对象都具备的功能。Object类中已经提供了对对象是否相同的比较方法。如果自定义类中也有比较相同的功能，没有必要重新定义。只要沿袭父类中的功能，建立自己特有比较内容即可。这就是覆盖。*/class Demo //extends Object{private int num;Demo(int num){this.num = num;