實現單例模式的幾種方式

1：餓漢模式

public class MyObject {
  // 當即加載方式 == 餓漢模式
  private static MyObject myObject= new MyObject();
  private MyObject(){}
  public static MyObject getInstance(){
    return myObject;
  }
}

2：懶漢模式

public class MyObject {
  private static MyObject myObject;
  private MyObject(){}
  synchronized public static MyObject getInstance(){
    if (myObject == null) {
      myObject = new MyObject();
    }
    return myObject;
  }
}

注意：加入同步synchronized關鍵字獲得相同實例的對象，但此種方式的運行效率很是低。

解決方法：使用DCL（Double-Check Locking）

public class MyObject {
  private static MyObject myObject;
  private MyObject(){}
  public static MyObject getInstance(){
    if (myObject == null) {
      synchronized (MyObject.class) {
        if (myObject == null) {
          myObject = new MyObject();
        }
      }
    }
    return myObject;
  }
}

3：靜態內置類

public class MyObject {
    private static class MyObjectHandler{
        private static MyObject myObject = new MyObject();
    }
    private MyObject() {
    }
    synchronized public static MyObject getInstance() {
        
        return MyObjectHandler.myObject;
    }
}

4：序列化與反序列化的單例模式實現

public class MyObjectSerializable implements Serializable {
    private static final long serialVersionUID = 888L;
     private static class MyObjectHandler{
         private static final MyObjectSerializable myObject = new MyObjectSerializable();
     }
     private MyObjectSerializable() {

     }
     protected Object readResolve() throws ObjectStreamException {
         return MyObjectHandler.myObject;
     }

}

5：使用靜態代碼塊

public class MyObject {
    private static MyObject myObject;
    static {
        myObject = new MyObject();
    }
    private MyObject() {
    }
    synchronized public static MyObject getInstance() {

        return myObject;
    }
}

6：使用enum枚舉數據類型