无法从文件中读取对象并将其放置到Java中的链表 [英] Can't read objects from file and place them to linkedlist in java

问题描述

我想从文件中读取对象并将数据放置到 LinkedList 中，并返回对其的引用.但是当我尝试这种方法时，它会返回没有数据的LinkedList.

I want to read object from a file and place data to a LinkedList and return the reference to it. But when I try this method it returns LinkedList that have no data.

private static LinkedList<Course> readFromFile(String fileName)
        throws FileNotFoundException, IOException {
    LinkedList<Course> tmp = new LinkedList<Course>();

    reader = new ObjectInputStream(new FileInputStream(fileName));

    try {
        LinkedList<Course> readObject2 = (LinkedList<Course>) reader
                .readObject();
        LinkedList<Course> readObject = readObject2;
        tmp = readObject;
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

    return tmp;
}

我的写作方法是这样的

private static boolean writeToFile(String fileName, LinkedList<Course> templist)
        throws IOException {
    LinkedList<Course> templist1 = new LinkedList<Course>();

    if (createFile(fileName)) {
        FileOutputStream outF = new FileOutputStream(fileName);

        outO = new ObjectOutputStream(outF);
        outO.writeObject(templist1);

        //outO.flush();
        return true;
    }
    else
        return false;
}

---

书写方法如下

---

Writing method looks like this

private static boolean writeToFile(String fileName, LinkedList<Course> templist) throws IOException {
    LinkedList<Course> templist1 = new LinkedList<Course>();

    if (createFile(fileName)) {
        FileOutputStream outF = new FileOutputStream(fileName);

        outO = new ObjectOutputStream(outF);
        outO.writeObject(templist1);

        //outO.flush();
        return true;
    }
    else
        return false;
}

推荐答案

Course类正在实现

The Course class is implementing java.io.Serializable ?
When you read objects from a file with ObjectInputStream it should be in the same order that you stored it with ObjectOutputStream before. And with the same objects types.

如果您尝试阅读:

 (LinkedList<Course>) reader.readObject();

您必须将其存储为:

ObjectOutputStream writer = new ObjectOutputStream(
        new FileOutputStream(fileName));

writer.writeObject(yourLinkedListToSave);

如代码所示:

private static boolean writeToFile(String fileName, LinkedList<Course> templist) throws IOException {
    // Dont forget to initialize with your list else the list still empty
    LinkedList<Course> templist1 = new LinkedList<Course>(templist);

    if (createFile(fileName)) {
        FileOutputStream outF = new FileOutputStream(fileName);

        outO = new ObjectOutputStream(outF);
        outO.writeObject(templist1);

        //outO.flush();
        return true;
    }
    else
        return false;
}

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