JAVA设计模式

单例设计模式属于创建型模式,提供了一种创建对象的最佳方式
基本思想:保证一个类中只能有一个实例,避免频繁的创建和销毁对象,减少内存开销, 并提供一个访问它的全局 访问点
避免对资源的多重占用(比如写文件操作)

package cn.tedu.java;


public class Singleton {
  public static void main(String[] args) {
    MySingleton1 s1 = MySingleton1.getInstance();
    MySingleton1 s2 = MySingleton1.getInstance();
    System.out.println(s1 == s2);
    System.out.println(s1.equals(s2));

    MySingleton2 s3 = MySingleton2.getInstance();
    MySingleton2 s4 = MySingleton2.getInstance();
    System.out.println(s3 == s4);
    System.out.println(s3.equals(s4));
  }
}


class MySingleton1 {
  private MySingleton1() {}

  private static final MySingleton1 singleton = new MySingleton1();

  public static MySingleton1 getInstance() {
    return singleton;
  }
}


class MySingleton2{
    private MySingleton2(){}
    private static MySingleton2 singleton;
    public static MySingleton2 getInstance(){
        if (singleton==null){
            synchronized (MySingleton2.class){
                if (singleton==null){
                    singleton=new MySingleton2();
                }
            }
        }
        return singleton;
    }
}