马士兵设计模式笔记1之单例的几种实现方式

来源：互联网发布：软件测试测试方法编辑：程序博客网时间：2024/05/14 21:13

//第一种 classic

public class Singleton{

private static Singleton uniqueInstance;
//other useful instance variables here

private Singleton(){}

public static Singleton getInstance(){
if(uniqueInstance==null){
uniqueInstance=new Singleton();
}

return uniqueInstance;
}

}

//第二种 synchronize

public class Singleton{

private static Singleton uniqueInstance;
//other useful instance variables here

private Singleton(){}

public static synchronized Singleton getInstance(){
if(uniqueInstance==null){
uniqueInstance=new Singleton();
}

return uniqueInstance;
}

}

//第三种 eagerly create
public class Singleton{

private static Singleton uniqueInstance=new Singleton();

private Singleton(){}

public static Singleton getInstance(){

return uniqueInstance;
}

}

//第四种双检锁
public class Singleton{

private volatile static Singleton uniqueInstance;
private int field1,field2;

private Singleton(){
//initialization
}

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

return uniqueInstance;
}

}

//第五种 lazy initiaization holder class

public class SingletonFactory{

private static class SingletonHolder{
public static Singleton instance=new Singleton();
}

public static Singleton getInstance(){
return SingletonHolder.instance;
}

}

//第六种 Enum Singleton
public enum Elvis{
INSTANCE;
public void leveTheBuiling(){
//.............
}
}

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