刚看到接口、多态，有点迷糊了。求解 - 黑马程序员技术交流社区

interface PCI
{
public abstract void open();
public abstract void close();
}
class NetCard implements PCI
{
public void open(){
System.out.println("netcard open");
}
public void close(){
System.out.println("netcard close");
}
}
class SoundCard implements PCI
{
public void open(){
System.out.println("SoundCard open");
}
public void close(){
System.out.println("SoundCard close");
}
}
class MainBroad
{
public void run(){
System.out.println("mainborad run");
}
/* 此处难以想到，意思有点绕不过来，也看，明白是用多态特性，传个父类引用对象进去，实现子类复写父类方法，但是总感觉要是自己想，就想不到这个做法的感觉。。。有点迷糊*/
public void usePCI(PCI p){
p.open();
p.close();
}
}
class Demo
{
public static void main(String []args){
MainBroad mb = new MainBroad();
mb.run();
mb.usePCI(new NetCard());
mb.usePCI(new SoundCard());
}
}

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