Java设计模式（四） 单例模式

方式一

package com.pattern.Singleton;

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

方式二

package com.pattern.Singleton;

public class Singleton2 {
	
	private static Singleton2 uniqueInstance = new Singleton2();
	
	private Singleton2(){}
	
	public static Singleton2 getInstance(){
		return uniqueInstance;
	}
}

方式三

package com.pattern.Singleton;

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