java设计模式之单例模式学习

package org.scott.singleton;
/**
 * @author Scott
 * @version 2013-11-16
 * @description
 */
public class Singleton1 {
    private static Singleton1 uniqueInstance = new Singleton1();

    private Singleton1(){

    }

    public static Singleton1 getInstance(){
        return uniqueInstance;
    }
}

package org.scott.singleton;
/**
 * @author Scott
 * @version 2013-11-16
 * @description
 */
public class Singleton2 { 

    private Singleton2() { 
    } 

    /**
     * 此处使用一个内部类来维护单例
     * */ 
    private static class SingletonFactory { 
        private static Singleton2 instance = new Singleton2(); 
    } 

    public static Singleton2 getInstance() { 
        return SingletonFactory.instance; 
    } 

    /**
     * 如果该对象被用于序列化，可以保证对象在序列化前后保持一致
     * */ 
    public Object readResolve() { 
        return getInstance(); 
    } 
}

package org.scott.singleton;
/**
 * @author Scott
 * @version 2013-11-16
 * @description
 */
public class Singleton3 {
    private volatile static Singleton3 uniqueInstance;

    private Singleton3(){

    }

    public static Singleton3 getInstance(){
        if(uniqueInstance == null){
            synchronized(Singleton3.class){
                if(uniqueInstance == null){
                    uniqueInstance = new Singleton3();
                }
            }
        }
        return uniqueInstance;
    }
}