单例模式

package mode.single;

public class Single {
	private static Single single;

	private Single() {
	}

	public static Single getInstance() {
		if (null == single) {
			System.out.println("第一次创建");
			single = new Single();
		}
		return single;
	}

}

测试

package mode.single;

public class Test {
	public static void main(String[] args) {
		Single s1 = Single.getInstance();
		Single s2 = Single.getInstance();
		Single s3 = Single.getInstance();
	}
}