一、

/**

 * lazy man(不是线程安全的)

 * @author TMAC-J

 *

 */

public class Singleton {

	private static Singleton instance;

	private Singleton(){}

	public static Singleton getInstance(){

		if(instance!=null){

			instance = new Singleton();

			}

		return instance;

	}

}

二、

/**

 * lazy man（线程安全）

 * @author TMAC-J

 *

 */

public class Singleton {

	private static Singleton instance;

	private Singleton(){}

	public static synchronized Singleton getInstance(){

		if(instance!=null){

			instance = new Singleton();

			}

		return instance;

	}

}

三、

/**

 * hungry man（天生线程安全,缺点是类加载的时候就会实例化）

 * @author TMAC-J

 *

 */

public class Singleton {

	private static Singleton instance = new Singleton();

	private Singleton(){}

	public static Singleton getInstance(){

		return instance;

	}

}

四、

这种写法和上面效果一样

public class Singleton {

    private Singleton instance = null;

    static {

    instance = new Singleton();

    }

    private Singleton (){}

    public static Singleton getInstance() {

    return this.instance;

    }

}

五、

/**

 * 静态内部类

 *

 * @author TMAC-J

 *

 */

public class Singleton {

	private static class SingletonHolder {

		private static  final Singleton instance = new Singleton();

	}

	private Singleton(){};

	public static final Singleton getSinleton(){

		return SingletonHolder.instance;

	}

}

六、

public enum Singleton {

    INSTANCE;

}  

七、

/**

 * 双重锁

 *

 * @author TMAC-J

 *

 */

public class Singleton {

	private static Singleton instance;

　　　　 private Singleton(){}

	public static Singleton getInstance(){

		if(instance == null){

			synchronized (Singleton.class) {

				if(instance == null){

					instance = new Singleton();

				}

			}

		}

		return instance;

	}

}

最常用的就是双重锁了，效率还可以