单例模式

 从网上整理了几种单例模式的例子

/**
 * 懒汉单例模式1
 * @author Administrator
 *
 */

public class SlugSingleton {
    private static SlugSingleton instance = null;

    private SlugSingleton(){};

    synchronized public static SlugSingleton getInstance(){
        if(instance == null){
            instance = new SlugSingleton();
            return instance;
        }
        else return instance;
    }
}

/**
 * 懒汉单例模式2
 * @author Administrator
 *
 */
public class SlugSingleton2{
    private static SlugSingleton2 instance = null;
    private static Object synObject = new Object();

    private SlugSingleton2(){};

    public static SlugSingleton2 getInstance(){
        if(instance != null) return instance;

        synchronized(synObject){
            if(instance == null){
                instance = new SlugSingleton2();
            }
        }

        return instance;
    }
}

/**
 * 饿汉单例模式
 * @author Administrator
 *
 */
public class HungrySingleton{
    private static final HungrySingleton instance = new HungrySingleton();

    private HungrySingleton(){};

    public static HungrySingleton getInstance(){
        return instance;
    }
}

/**
 * 一种新的单例模式
 * @author Administrator
 *
 */
public class NewSingleton {

    public static NewSingleton getInstance() {
        return TestInstance.getInstance();
    }

    private NewSingleton() {
    }

    private static class TestInstance {
        private static NewSingleton instance = new NewSingleton();

        private TestInstance() {
        }

        private static NewSingleton getInstance() {
            return instance;
        }
    }
}