无法转换为 java.util.ArrayList

Question

尝试将对象写入数组，然后保存到output.data，然后再次读取对象。

写作：

private void saveBtnActionPerformed(java.awt.event.ActionEvent evt) {                                        

    File outFile;
    FileOutputStream fStream;
    ObjectOutputStream oStream;

    try {
        outFile = new File("output.data");
        fStream = new FileOutputStream(outFile);
        oStream = new ObjectOutputStream(fStream);

        oStream.writeObject(arr);

        JOptionPane.showMessageDialog(null, "File Written Successfully");

        oStream.close();
    } catch (IOException e) {
        System.out.println("Error: " + e);
    }
}                  

阅读：

private void readBtnActionPerformed(java.awt.event.ActionEvent evt) {                                        

    File inFile;
    FileInputStream fStream;
    ObjectInputStream oStream;

    try {
        inFile = new File("output.data");
        fStream = new FileInputStream(inFile);
        oStream = new ObjectInputStream(fStream);

        //create an array of assessments
        ArrayList <Assessment> xList;
        xList = (ArrayList<Assessment>)oStream.readObject();



        for (Assessment x:xList) {
            JOptionPane.showMessageDialog(null, "Name: " + x.getName() + "Type: " + x.getType() + "Weighting: " + x.getWeighting());
        }

        oStream.close();
    } catch (IOException e) {
        System.out.println("Error: " + e);
    } catch (ClassNotFoundException ex) {
        System.out.println("Error: " + ex);
    }


}                      

代码编译得很好，文件本身也保存得很好。但是当我尝试读取该文件时，没有任何反应，NetBeans 说

“线程“AWT-EventQueue-0”java.lang.ClassCastException 中出现异常：[Lnetbeansswingexample.Assessment；无法转换为 java.util.ArrayList”

造成麻烦的代码行似乎是

xList = (ArrayList<Assessment>)oStream.readObject();

任何帮助将不胜感激，谢谢。抱歉，如果答案显而易见，对于编程来说还很陌生。

Answer 1

根据您得到的异常，它看起来oStream.readObject()返回一个 数组Assessment，而不是List. 您可以将其转换为List：

    List <Assessment> xList;
    xList = Arrays.asList((Assessment[])oStream.readObject());

或者如果您必须使用java.util.ArrayList：

    ArrayList<Assessment> xList;
    xList = new ArrayList<> (Arrays.asList((Assessment[])oStream.readObject()));