7.单例模式(Singleton)

单例模式就是确保一个类只有一个实体，并且该实例心须自动创建，并向整个系统提供该实例.

下面是两个例子,饿汉式单例模式与懒汉式单例模式:

 

 

public class Singleton1 {

	private static Singleton1 instance = new Singleton1();
	protected Singleton1() {	
	}	
	
	public static Singleton1 getInstance(){
		return instance;
	}
	
	

}

 

 

 

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

}