java 三种单例模式

目录

​​饿汉单例模式​​

​​懒汉双锁单例模式​​

​​懒汉静态内部类单例模式​​

​​调用测试​​

​​输出结果​​

---

饿汉单例模式

/**
 * 单例模式 饿汉式
 * 线程安全，调用效率高，但是不能延时加载
 */
public class HungrySimpleInstance {
    private HungrySimpleInstance(){
        System.out.println("初始化 HungrySimpleInstance");
    }
    private static HungrySimpleInstance simpleInstance = new HungrySimpleInstance();
    public static HungrySimpleInstance getSimpleInstance(){
        return simpleInstance;
    }

    public String getName(){
        return "饿汉单例模式：HungrySimpleInstance";
    }
}

懒汉双锁单例模式

/**
 * 单例模式 懒汉双锁式
 */
public class LazyLockSimpleInstance {
  private LazyLockSimpleInstance(){
      System.out.println("初始化 LazyLockSimpleInstance");
  }
  private static volatile LazyLockSimpleInstance simpleInstance;
  public static LazyLockSimpleInstance getSimpleInstance(){
      if (simpleInstance==null){
          synchronized(LazyLockSimpleInstance.class){
              if (simpleInstance==null){
                  simpleInstance = new LazyLockSimpleInstance();
              }
          }
      }
      return simpleInstance;
    }

    public String getName(){
      return "懒汉双锁单例模式：LazyLockSimpleInstance";
    }
}

懒汉静态内部类单例模式

/**
 * 单例模式 懒汉静态内部类式
 * 线程安全，调用效率高，可以延时加载
 */
public class LazyStaticClassSimpleInstance {
    private LazyStaticClassSimpleInstance(){
        System.out.println("初始化 LazyStaticClassSimpleInstance");
    }

    public static LazyStaticClassSimpleInstance getSimpleInstance(){
        return LazyStaticClassSimpleInstanceHold.simpleInstance;
    }
    private static class LazyStaticClassSimpleInstanceHold{
        private static final LazyStaticClassSimpleInstance simpleInstance = new LazyStaticClassSimpleInstance();
    }

    public String getName(){
        return "懒汉静态内部类单例模式：LazyStaticClassSimpleInstance";
    }
}

调用测试

public static void main(String[] args) throws InterruptedException, ExecutionException {
       System.out.println(HungrySimpleInstance.getSimpleInstance().getName());
       System.out.println(LazyLockSimpleInstance.getSimpleInstance().getName());
       System.out.println( LazyStaticClassSimpleInstance.getSimpleInstance().getName());
    }

输出结果

初始化 LazyLockSimpleInstance
懒汉双锁单例模式：LazyLockSimpleInstance
初始化 LazyStaticClassSimpleInstance
懒汉静态内部类单例模式：LazyStaticClassSimpleInstance