java编程，求解答，只要代码，谢谢

Question

如题所述

Answer 1

abstract class Instrument
{
public abstract void play();
}

class Piano extends Instrument
{
public void play()
{
System.out.println("Piano is playing.");
}
}

class Violia extends Instrument
{
public void play()
{
System.out.println("Violia is playing.");
}
}

public class InstrumentTest()
{
public static void testPlay(Instrument instrument)
{
instrument.play();
}

public static void main(String[] args)
{
testPlay(new Piano());
testPlay(new Violia());
}
}