public class Strategy {

	public ClassSelector getInstance() {
		final boolean isWin = System.getProperty("os.name").startsWith(
				"Windows");
		final boolean isMac = System.getProperty("os.name").startsWith("Mac");
		final boolean isLinux = System.getProperty("os.name").startsWith(
				"Linux");

		if (isWin) {
			return new WinImpl();
		} else if (isMac) {
			return new MacImpl();
		} else if (isLinux) {
			return new LinuxImpl();
		} else {
			System.out.println("OS nicht feststellbar");
		}
		return null;
	}

	public static void main(String[] args) {
		Strategy str = new Strategy();
		ClassSelector inter = str.getInstance();
		inter.printOS();
	}
}

class WinImpl implements ClassSelector {
	public void printOS() {
		System.out.println("Windows");
	}
}

class MacImpl implements ClassSelector {
	public void printOS() {
		System.out.println("Mac OS X");
	}
}

class LinuxImpl implements ClassSelector {
	public void printOS() {
		System.out.println("Linux");
	}
}

interface ClassSelector {
	public void printOS();
}