Java实现单例模式总结

单例模式（Singleton）：是一种常用的设计模式。在Java应用中，单例对象能保证在一个JVM中，该对象只有一个实例存在。

1、懒汉式
线程不安全，当有多个线程并行调用 getInstance() 的时候，就会创建多个实例。

public class Singleton {
    private static Singleton instance;
    private Singleton (){}
    public static Singleton getInstance() {
     if (instance == null) {
         instance = new Singleton();
     }
     return instance;
    }
}

public class Singleton{
    //类加载时就初始化
    private static final Singleton instance = new Singleton();
    
    private Singleton(){}
    public static Singleton getInstance(){
        return instance;
    }
}

public class Singleton {
    private volatile static Singleton instance; //声明成 volatile
    private Singleton (){}
    public static Singleton getSingleton() {
        if (instance == null) {                         
            synchronized (Singleton.class) {
                if (instance == null) {       
                    instance = new Singleton();
                }
            }
        }
        return instance;
    } 
}

public class Singleton {  
    private static class SingletonHolder {  
        private static final Singleton INSTANCE = new Singleton();  
    }  
    private Singleton (){}  
    public static final Singleton getInstance() {  
        return SingletonHolder.INSTANCE; 
    }  
}

public enum EnumSingleton{
    INSTANCE;
}

Java实现单例模式总结

原文：http://blog.csdn.net/lgcssx/article/details/43990971