Java Error java.lang.NullPointerException 2

Question

    public FileWindow(JMenuItem menuItem,final JTextArea text, JMenuItem save){

    //Open
    menuItem.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent event){
            openFile();

            if(fileToOpen == JFileChooser.APPROVE_OPTION){
                text.setText("");
                try{
                    Scanner scan = new Scanner(new FileReader(Open.getSelectedFile().getPath()));
                    while(scan.hasNext()){
                        text.append(scan.nextLine() + "\n");
                    }
                }catch(Exception e){
                    System.out.println(e.getMessage());
                }
            }
        }
    });

    //Save
    save.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent event){
            saveFile();
            if(fileToSave == JFileChooser.APPROVE_OPTION){
                try{
                    BufferedWriter out = new BufferedWriter(new FileWriter(Save.getSelectedFile().getPath() + ".txt"));
                    out.write(text.getText());
                    out.flush();
                    out.close();

                }catch(Exception e){
                    System.out.println(e.getMessage());
                }
            }
        }
    });
}

我在这一行收到错误 - ＆gt; “menuItem.addActionListener（new ActionListener）{”我尝试启动变量，但这不起作用。任何帮助将非常感谢！

Answer 1

您最有可能获得NullPointerException，因为menuitem为空。确保在调用此构造函数之前初始化menuitem。

Answer 2

当您运行menuItem

时，

menuItem.addActionListener()为空

确保它不为空，但添加：

if (menuItem == null)
    System.out.println("menuItem is null!");