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);
    }
}                  

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);
    }


}                      

代码可以很好地编译，文件本身也可以保存。 但是当我尝试读取文件时，什么也没发生，NetBeans说

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

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，如果答案很明显，那么这对编程来说还很陌生。

Answer 1

根据您得到的异常，看起来oStream.readObject()返回一个Assessment数组，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()));