Java Basics Introduction Essay (10) JavaSE Edition - Singleton Design Pattern

Design patterns: effective solutions to problems. In fact, it is a thought.

1. Singleton design pattern.

The problem solved: It can ensure the uniqueness of objects of a class in memory. (Single instance)

Requirements for using the singleton design pattern: When the same configuration information object must be used for multiple programs, the uniqueness of the object needs to be ensured.

How to ensure object uniqueness?                                                                                                                                                                                                                                                                                                       Solution steps:                                                                                                                                   

2. Create an instance of this class in this class. 2. Create an object in this category through New.

3. Provide a method for other programs to obtain the object.                        3. Define a public method to return the created object.

//饿汉式（开发时常用）
class Single//类一加载，对象就已经存在了。
{
	private static Single s = new Single();

	private Single(){}

	public static Single getInstance()
	{
		return s;
	}
}


//懒汉式（面试时常问，在多线程并发访问时候有可能导致不能保证不了对象的唯一性,存在安全隐患！）
class Single2//类加载进来，没有对象，只有调用了getInstance方法时，才会创建对象。
			//延迟加载形式。 
{
	private static Single2 s = null;

	private Single2(){}

	public static Single2 getInstance()
	{
		if(s==null)
			s = new Single2();
		return s;
	}
}

//调用类
class  SingleDemo
{
	public static void main(String[] args) 
	{
		Single s1 = Single.getInstance();
		Single s2 = Single.getInstance();

		System.out.println(s1==s2);
		
//		Single ss = Single.s; //此处不采用这个是因为不可控，采用 Single.getInstance();可以传参数进行相应调用。

	}
}

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