6.synchronized的使用注意点

package basic.single;

public class SingleTon {

  private SingleTon(){
    System.out.println(Thread.currentThread().getName());
  }

  private static volatile SingleTon singleTon;

  /*public static SingleTon getInstance(){
    if(singleTon == null){
      synchronized (SingleTon.class){
        if(singleTon == null){
          singleTon = new SingleTon();
        }
      }
    }
    return singleTon;
  }*/

  public static synchronized SingleTon getInstance(){
    if(singleTon == null){
      singleTon = new SingleTon();
    }
    return singleTon;
  }

  public static void main(String[] args) {
    for (int i = 0; i < 10; i++) {
      new Thread(()->{
        SingleTon.getInstance();
      }).start();
    }
  }

}