public class SingleTest {
  public static final SingleTest singleTest1=new SingleTest();

  public SingleTest() {
  }
  public static SingleTest getSingleTest1(){

    return singleTest1;
  }
}

public class SingleTest1 {


  private static SingleTest1 instance=null;

  public SingleTest1() {
  }
  public static SingleTest1 getInstance(){
    if(instance==null){
      instance=new SingleTest1();
    }
    return instance;
  }
}

public class SingleTest2 {

  private static SingleTest2 instance=null;

  public SingleTest2() {
  }
  public static synchronized SingleTest2 getInstance(){
    if(instance==null){
      instance=new SingleTest2();
    }
    return instance;
  }
}

public class SingleTest4 {
  private static SingleTest4 instance=null;//靜態(tài)變量
  public SingleTest4() {
  }
  public static SingleTest4 getInstance(){
    if (instance == null) {//第一層校驗(yàn)
      synchronized (SingleTest4.class) {
        if (instance == null) {//第二層校驗(yàn)
          instance = new SingleTest4();
        }
      }
    }
    return instance;
  }
}

public class SingleTest5 {
  private SingleTest5() {
  }

  public static final SingleTest5 getInstance() {
    return SingletonHolder.INSTANCE;
  }

  //定義的靜態(tài)內(nèi)部類(lèi)
  private static class SingletonHolder {
    private static final SingleTest5 INSTANCE = new SingleTest5(); //創(chuàng)建實(shí)例的地方
  }
}

public enum SingleTest6 {
  //第一種方式
//  INSTANCE;
//  private CaiPiao instance;
//
//  SingleTest6() {
//    instance = new CaiPiao();
//  }
//
//  public CaiPiao getInstance() {
//    return instance;
//  }
//
//  class CaiPiao {
//
//  }


//第二種方式
  INSTANCE2{
    @Override
    protected void CaiPiao() {
      System.out.println("彩票");
    }

  };
  protected abstract void CaiPiao();
}