DCL雙檢查鎖機制

public class MyConfig {
    private volatile static MyConfig myConfig = null;//volatile 保證每個執行緒都是從主存中讀取最新的資料

    private MyConfig(){

    }
    public static MyConfig getInstance(){
        if(null != myConfig){

        }else {
            //同步程式碼塊
            synchronized (MyConfig.class){
                if
 
(null == myConfig){
                    myConfig = new MyConfig();
                }
            }
        }
        return myConfig;
    }
}

靜態內建類

public class MyConfig {

    private MyConfig(){}

    private static class MyConfigHandler{
        private static MyConfig myConfig = new MyConfig();
    }

    public
 
 static MyConfig getInstance(){
        return MyConfigHandler.myConfig;
    }
}

序列化和反序列化

public class MyConfig implements Serializable{
    private volatile static MyConfig myConfig = null;//volatile 保證每個執行緒都是從主存中讀取最新的資料

    private MyConfig(){

    }
    public static MyConfig getInstance(){
        if
 
(null != myConfig){

        }else {
            //同步程式碼塊
            synchronized (MyConfig.class){
                if(null == myConfig){
                    myConfig = new MyConfig();
                }
            }
        }
        return myConfig;
    }

    //單例類需實現這個方法，readResolve方法應對單例物件被序列化時候
    public Object readResolve(){
        return getInstance();
    }

    public static MyConfig getMyConfig(){

        try {
            MyConfig myConfig = MyConfig.getInstance();
            FileOutputStream fileOutputStream = new FileOutputStream(new File("myobject.txt"));
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
            objectOutputStream.writeObject(myConfig);
            objectOutputStream.close();
            fileOutputStream.close();
            System.out.println(myConfig.hashCode());
        }catch (Exception e){
            e.printStackTrace();
        }
        MyConfig myConfig = null;
        try {
            FileInputStream fileInputStream = new FileInputStream(new File("myobject.txt"));
            ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
            myConfig = (MyConfig) objectInputStream.readObject();
            objectInputStream.close();
            fileInputStream.close();
            System.out.println(myConfig.hashCode());
        }catch (Exception e){
            e.printStackTrace();
        }
        return myConfig;
    }
}

靜態程式碼塊

public class MyConfig{
    private static MyConfig myConfig = null;

    private MyConfig(){}

    static{
        myConfig = new MyConfig();
    }

    public static MyConfig getInstance(){
        return myConfig;
    }
}

列舉實現

public class MyConfig {

    public enum MyConfigEnum{
        connectionFactofry;
        private MyConnection myConnection = null;
        private MyConfigEnum(){
            myConnection = new MyConnection();
        }
        public MyConnection getMyConnection(){
            return myConnection;
        }
    }
    public static MyConnection getConnection(){
        return MyConfigEnum.connectionFactofry.getMyConnection();
    }
}

public class MyConnection {
    public MyConnection(){

    }
}