Question

我创建了一个程序来计算某些东西并将信息存储到hashTable中。我想要它做的是下次它运行以恢复存储在hashTable和resume中的先前值。所以我问如何将对象保存到文件中？

在我的代码中，我使用的是FileInputStream和FileOutputStream。到目前为止，这是我的代码的一小段内容：

@SuppressWarnings("unchecked")
private void obtainSaveFile(){
    String file = new String("./saveFile.txt");
    try{
        //Create the file if it doesn't exist
        if( !( (new File(file)).exists() ) ){

            //Create new empty file
            (new File(file)).createNewFile();

            //Creates a fresh new hashTable
            hashTable = new QuadraticProbingHashTable<TicTacToeBoard>();
        }
        else{
            //Obtain the hashTables saved config.txt file
            FileInputStream fis = new FileInputStream(file);
            ObjectInputStream ois = new ObjectInputStream(fis);

            //Obtain the previously saved hashTable
            //-----------------------------------
            //This line of code gives me an error
            //-----------------------------------
            hashTable = (QuadraticProbingHashTable<TicTacToeBoard>)ois.readObject();
            ois.close();
        }

        //Create save file configs.txt
        FileOutputStream fos = new FileOutputStream(file);
        saveFile = new ObjectOutputStream(fos);     

    }catch(Exception e){
        e.printStackTrace();

        //Creates a fresh new hashTable
        //This line of code gives me an error
        hashTable = new QuadraticProbingHashTable<TicTacToeBoard>();
    }
}

最初，当没有文件时，它运行正常。但在那之后，它一直给我错误。当我从文件中取出一个对象并将其转换为QuadraticProbingHashTable并将其设置为hashTable时，它并不喜欢。

此外，这里输出的是错误：

java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: proj4.QuadraticProbingHashTable$HashEntry
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readArray(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
    at java.io.ObjectInputStream.readSerialData(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at proj4.TicTacToeSolver.obtainSaveFile(TicTacToeSolver.java:308)
    at proj4.TicTacToeSolver.solve(TicTacToeSolver.java:120)
    at proj4.Main.main(Main.java:41)
Caused by: java.io.NotSerializableException: proj4.QuadraticProbingHashTable$HashEntry
    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
    at java.io.ObjectOutputStream.writeArray(Unknown Source)
    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
    at java.io.ObjectOutputStream.defaultWriteFields(Unknown Source)
    at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
    at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
    at java.io.ObjectOutputStream.writeObject(Unknown Source)
    at proj4.TicTacToeSolver.solve(TicTacToeSolver.java:246)
    ... 1 more
Exception in thread "main" java.lang.NullPointerException
    at proj4.TicTacToeSolver.solve(TicTacToeSolver.java:246)
    at proj4.Main.main(Main.java:41)

Answer 1

嗯，问题似乎是，你正在尝试序列化一些没有实现Serializable的东西。你可以在这里看到：

java.io.NotSerializableException: proj4.QuadraticProbingHashTable$HashEntry

您有两种选择：

如果可能的话，让HashEntry实现Serializable
您将其标记为瞬态，因此不会被序列化（可能不是您想要的）。

有关详细信息，您可以发布课程。

Answer 2

问题在于，即使您的表可能是可序列化的，您也可以向哈希表添加一个键或值，该键不可序列化。所有对象都可以进入Hashtable，但并非所有对象都可以序列化。你在哈希表中放入了什么样的对象？

如何从文件中保存和检索hashTable？

2 个答案: