public class InterfacePolyArr {
    public static void main(String[] args) {

        Usb[] usbs = new Usb[2];
        usbs[0] = new Phone();
        usbs[1] = new Camera();

        for (int i = 0; i < usbs.length; i++) {
            usbs[i].work();
            // 判断运行类型是否是Phone
            if (usbs[i] instanceof Phone) {
                ((Phone)usbs[i]).cal();
            }
        }
    }
}

interface Usb{
    void work();
}
class Phone implements Usb{
    public void cal(){
        System.out.println("手机可以打电话");
    }

    @Override
    public void work() {
        System.out.println("手机工作中");
    }
}
class Camera implements Usb{
    public void photo() {
        System.out.println("相机可以拍照");
    }

    @Override
    public void work() {
        System.out.println("相机工作中");
    }
}