Explanation of singleton pattern in java design patterns

I learned that there are 23 design patterns in Java. Design patterns are summaries of code experience that are known to most people, used repeatedly, and are conventional. Each design pattern represents a problem that will occur repeatedly in the project, so the reasonable use of design patterns can perfectly solve many problems.

It is necessary to learn Java design patterns. Although inheritance and interfaces have not been learned in object-oriented, the singleton pattern in the 23 design patterns can already be understood.

Singleton object is a commonly used design pattern. In Java applications, a singleton object can ensure that only one instance of the object exists in a JVM. There are two specific forms of expression:

package 面向对象;//单例设计模式第一种public class Singleton 
{public static void main(String[] args)
    {
    SingletonDemo a=SingletonDemo.getInstance();
    }
}class SingletonDemo
{private static SingletonDemo a =null;private SingletonDemo(){}public static SingletonDemo getInstance()
    {if(a==null)
        {
            SingletonDemo a=new SingletonDemo();
        }return a;
    }
}

This way can be seen that new objects are created only when the method is called, but it is easy to cause problems when using multiple threads. , so the following method is generally used for development.

 1 package 面向对象; 2  3 public class Singleton_2 
 4 { 5     public static void main(String[] args) 6     { 7         Singleton_2Demo a=Singleton_2Demo.getInstance(); 8     } 9 }10 11 class Singleton_2Demo12 {13     private Singleton_2Demo(){}14     private static Singleton_2Demo a=new Singleton_2Demo();15     public static Singleton_2Demo getInstance()16     {17         return a;18     }19 }

This method is simple and there is no need to consider multi-threading issues

Through this design pattern, we can learn more about the previous The object-oriented exercise I wrote was adjusted to implement the singleton pattern.

Original code:

package 面向对象; class Student 
{    private String name;private int number;private String sex;private boolean learn;private String a;
    Student()
     {
         name="未知";
         number=000;
         sex="未知";
         learn=false;
         a="未知";
     }     public void setName(String name)
     {         this.name=name;
     }     public void setNumber(int number)
     {         this.number=number;
     }     public void setSex(String sex)
     {         this.sex=sex;
     }     public void setLearn(boolean learn)
     {         this.learn=learn;
     }     void scan()
    {if(this.learn==true)
        {
            a="在学习";    
        }else{
            a="不在学习";
        }    
         System.out.print("姓名："+this.name+" 学号："+this.number+" 性别；"+this.sex+" 是否在学习:"+a);
    }
    
} class Data
 {     public static void main(String[] arg)
     {
         Student XiaoMin=new Student();
         XiaoMin.setName("小明");
         XiaoMin.setNumber(13023);
         XiaoMin.setSex("男");
         XiaoMin.setLearn(true);
         XiaoMin.scan();
     }
 }

Single case mode:

package 面向对象;//实现单例设计模式
 class Student_1 
{    private String name;private int number;private String sex;private boolean learn;private String a;     private Student_1()
     {
         name="未知";
         number=000;
         sex="未知";
         learn=false;
         a="未知";
     }     private static Student_1 b=new Student_1();     public static Student_1 getInstance()
     {         return b;
     }     public void setName(String name)
     {         this.name=name;
     }     public void setNumber(int number)
     {         this.number=number;
     }     public void setSex(String sex)
     {         this.sex=sex;
     }     public void setLearn(boolean learn)
     {         this.learn=learn;
     }     void scan()
    {if(this.learn==true)
        {
            a="在学习";    
        }else{
            a="不在学习";
        }    
         System.out.print("姓名："+this.name+" 学号："+this.number+" 性别；"+this.sex+" 是否在学习:"+a);
    }
    
} class Data_2
 {     public static void main(String[] arg)
     {
         Student_1 XiaoMin=Student_1.getInstance();
         XiaoMin.setName("小王");
         XiaoMin.setNumber(13023);
         XiaoMin.setSex("男");
         XiaoMin.setLearn(true);
         XiaoMin.scan();
     }
 }

The above is the detailed content of Explanation of singleton pattern in java design patterns. For more information, please follow other related articles on the PHP Chinese website!