官术网_书友最值得收藏!

Sample implementation of the Singleton design pattern

In the following code example, I will be creating a class with a method to create an instance of this class if one does not exist. If the instance is already present, then it will simply return the reference of that object. I have also taken thread safety into consideration, and so I have used a synchronized block here before creating the object of that class.

Let's check out the UML diagram for the Singleton design pattern:

    package com.packt.patterninspring.chapter2.singleton.pattern; 
    public class SingletonClass { 
      private static SingletonClass instance = null; 
      private SingletonClass() { 
      } 
      public static SingletonClass getInstance() { 
        if (instance == null) { 
          synchronized(SingletonClass.class){   
               if (instance == null) { 
                  instance = new SingletonClass(); 
               } 
          } 
        } 
       return instance; 
      } 
    } 
  } 

One thing to be noted in the preceding code is that I have written a private constructor of the SingletonClass class to make sure that there is no way to create the object of that class. This example is based on lazy initialization, which means that the program creates an instance on demand the first time. So you could also eagerly instantiate the object to improve the runtime performance of your application. Let's see the same SingletonClass with eager initialization:

    package com.packt.patterninspring.chapter2.singleton.pattern; 
    public class SingletonClass { 
      private static final SingletonClass INSTANCE = 
new SingletonClass(); private SingletonClass() {} public static SingletonClass getInstance() { return INSTANCE; } }

Now that we've seen the singleton design pattern, let's turn to a different variant of it--the Prototype design pattern.

主站蜘蛛池模板: 兴文县| 从化市| 朝阳区| 尚志市| 五华县| 三明市| 黑河市| 东丰县| 沾化县| 郑州市| 慈溪市| 宜兰市| 南丹县| 丽江市| 洪洞县| 西昌市| 航空| 金湖县| 江永县| 双辽市| 达日县| 镇安县| 上杭县| 海晏县| 旬邑县| 吉首市| 常德市| 青海省| 静海县| 深泽县| 石河子市| 瓦房店市| 县级市| 临武县| 安宁市| 尚志市| 淮阳县| 扶沟县| 科尔| 自治县| 西城区|