The JAVA (singleton design pattern)

Copyright: qq836678589 https://blog.csdn.net/weixin_43924623/article/details/91344722

Introduced

What is a design pattern?
Effective solution to solve certain types of problems that arise.
(Java in a total of 23 design patterns)
What is the Singleton Design Pattern?
A class and then only with a memory object.
How to reflect?
First, the privatization of the constructor.
Secondly, the present construct a class object.
This method can obtain a class object.

Code reflects

Two objects of the same class

class A{
    private int num;

    public void setNum(int num){
        this.num=num;
    }
    public int getNum(){
        return num;
    }
    
}
public class Main {

    public static void main(String[] args){
        A a = new A();
        A b = new A();
        a.setNum(25);
        b.setNum(26);
        System.out.println(a.getNum());
        System.out.println(b.getNum());

    }
}

Singleton design pattern

class A{
    private int num;
    private static A s = new A();
    public static A getInstance(){
            return s;
    }
    public void setNum(int num){
        this.num=num;
    }
    public int getNum(){
        return num;
    }

}
public class Main {

    public static void main(String[] args){
        A a = A.getInstance();
        A b = A.getInstance();
        a.setNum(25);
        System.out.println(a.getNum());
        System.out.println(b.getNum());

    }
}