枚举类实现单例模式

实现单例模式时候，要思考四个问题：

1. 是否线程安全
2. 多线程安全了，效率是否能接受
3. 是否可以延迟加载
4. 是否支持序列化

请看下面一张图：

枚举实现单例模式如下：简洁优雅

public enum Singleton 0 {
    INSTANCE;
    int anInt;
 
    public int getAnInt() {
        return anInt;
    }
 
    public void setAnInt( int anInt ) {
        this.anInt = anInt;
    }
 
    public  void dosomethings(  ) {
        System.out.println("枚举类实现单例");
    }
}
 

恶汉式单例模式如下：

public class Singleton 1{
    private static Singleton instance = new Singleton();
    private Singleton(){}
    public static Singleton getInstance(){
        return instance;
    }
}

饱汉式单例模式

 
 
public class Singleton2 {
 
	private static Singleton2 singleton;
	
	private Singleton2(){
		
	}
	
	public static synchronized Singleton2 getInstance(){
		if(singleton == null) 
			singleton = new Singleton2();
		return singleton;
	}
 
 

双重锁模式(DCL):

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

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