题解 | #创建单例对象#

public class Main {

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

}

class Singleton {

  private static Singleton instance;

  private Singleton() {

  }

  // DCL懒汉
  public static Singleton getInstance() {
    if (instance == null) {
      synchronized (Singleton.class) {
        if (instance == null) {
          instance = new Singleton();
        }
      }
    }
    return instance;
  }

}