java编程思想第四版习题_8.9_java编程思想 8 . 9 练习-优快云博客

本文介绍了一个Java音乐系统，演示了如何通过接口和抽象类实现乐器类，支持不同类型的乐器如风琴、打击乐器和弦乐器，并展示了如何统一调用这些乐器演奏特定音符并进行调音。

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enum Note {
	MIDDLE_C;
}

interface Instrument {
	// Compile-time constant:
	int VALUE = 5; // static & final

	// Cannot have method definitions:
	void play(Note n); // Automatically public

	void adjust();
}

abstract class A {
	public void play(Note n) {
		System.out.println(this + ".play() " + n);
	}

	public void adjust() {
		System.out.println(this + ".adjust()");
	}
}

class Wind extends A implements Instrument {

	public String toString() {
		return "Wind";
	}

}

class Percussion extends A implements Instrument {

	public String toString() {
		return "Percussion";
	}

}

class Stringed extends A implements Instrument {

	public String toString() {
		return "Stringed";
	}

}

public class Music5 {
	// Doesn't care about type, so new types
	// added to the system still work right:
	static void tune(Instrument i) {
		// ...
		i.play(Note.MIDDLE_C);
	}

	static void tuneAll(Instrument[] e) {
		for (Instrument i : e)
			tune(i);
	}

	public static void main(String[] args) {
		// Upcasting during addition to the array:
		Instrument[] orchestra = { new Wind(), new Percussion(), new Stringed() };
		tuneAll(orchestra);
	}
}

打印结果

Wind.play() MIDDLE_C
Percussion.play() MIDDLE_C
Stringed.play() MIDDLE_C