设计模式之单例模式1,2.singleton

package liu.singleton.demo;

public class Singleton2 {

 private static Singleton2 instance = null;
 public static synchronized Singleton2 getInstance (){
  if(instance == null){
   instance = new Singleton2();
  }
  return instance;
 }
 public static void main(String[] args) {
  

 }

}
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package liu.singleton.demo;

public class Singleton1 {

 private Singleton1(){}
 private static Singleton1 instance = new Singleton1();
 private static Singleton1 getInstance(){
  return instance;
 }
}