单元素枚举类型singleton模块

public enum Elvis {
	INSTANCE;

	public void leaveTheBuilding() {
		System.out.println("Whoa baby, I'm outta here!");
	}

	// This code would normally appear outside the class!
	public static void main(String[] args) {
		Elvis elvis = Elvis.INSTANCE;
		elvis.leaveTheBuilding();
	}
}