直譯器模式：

        給定一中語言，定義它的文法的一種表示，並定義一個直譯器，這個直譯器使用該表示來解釋語言中的句子。

// 表示式類
public abstract class Expression {

	public void interpret(PlayContext context) {
		if (context.getContext().length() == 0) {
			return;
		} else {
			String playKey = context.getContext().substring(0, 1);
			context.setContext(context.getContext().substring(2));
			double playValue = Double.parseDouble(context.getContext().substring(0, context.getContext().indexOf(" ")));
			context.setContext(context.getContext().substring(context.getContext().indexOf(" ") + 1));

			excute(playKey, playValue);
		}
	}

	public abstract void excute(String key, double value);

}

// 音符類
public class Note extends Expression {

	@Override
	public void excute(String key, double value) {
		String note = null;
		if (key.equals("C"))
			note = "1";
		if (key.equals("D"))
			note = "2";
		if (key.equals("E"))
			note = "3";
		if (key.equals("F"))
			note = "4";
		if (key.equals("G"))
			note = "5";
		if (key.equals("A"))
			note = "6";
		if (key.equals("B"))
			note = "7";

		System.out.print(" " + note + " ");
	}

}

// 音階類
public class Scale extends Expression {

	@Override
	public void excute(String key, double value) {
		String scale = null;
		int intKey = (int) value;
		if (intKey == 1)
			scale = "low scale";
		if (intKey == 2)
			scale = "mid scale";
		if (intKey == 3)
			scale = "high scale";

		System.out.print(" " + scale + " ");
	}

}

// 演奏內容類
public class PlayContext {

	private String context;

	public String getContext() {
		return context;
	}

	public void setContext(String context) {
		this.context = context;
	}

}

// 客戶端
public class InterpreterMain {

	public static void main(String[] args) {
		PlayContext context = new PlayContext();
		String content = "O 2 E 0.5 G 0.5 A 3 E 0.5 G 0.5 D 3 E 0.5 G 0.5 A 0.5 O 3 C 1 O 2 A 0.5 G 1 C 0.5 E 0.5 D 3 ";
		context.setContext(content);

		Expression exp = null;
		try {
			while (context.getContext().length() > 0) {
				String str = context.getContext().substring(0, 1);

				if (str.equals("O")) {
					exp = new Scale();
				} else {
					exp = new Note();
				}
				exp.interpret(context);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}