java - 在 Java 中创建 GUI 时出现编译错误

Question

我的程序打开一个文件，允许您查看或编辑它，然后再次保存它。到目前为止，我只有 GUI 布局。

因此，当我尝试编译程序时，出现以下错误:

    FileChooser.java:26: error: <identifier> expected
         fileChooser = newJFileChooser();

我收到了 ^^^ 错误四次，对于我初始化的每个组件一次。

    FileChooser.java:39: error: invalid method declaration; return type required
         public FileChooserGUI() {

当我尝试创建构造函数时，出现此 ^^^ 错误。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.filechooser.*;

public class FileChooser extends JFrame { //JFrame is a container class in Swing

//declare all components and other variables
private JTextArea textArea; //b
private JButton openFileButton; //c
private JButton saveFileButton;
private JButton clearButton;

//Declare and initialize a JFileChooser object using JFileChooser's
//default constructor.
private JFileChooser fileChooser;
fileChooser = newJFileChooser();

//Declare and initialize a FileNameExtensionFilter object for .txt files.
private FileFilter fileFilter;
fileFilter = new FileNameExtensionFilter("text file", "txt");

//Set the JFileChooser object's current file filter by calling it's
//setFileFilter method and passing it the filter you created in e.
fileChooser.setFileFilter(fileFilter);


//constructor - initialize all components, add them to the container, 
//create listener objects, register them to listen for events
public JFileChooserLabGUI() {

    //call superclass constructor
    super("File Chooser");


    //initialize all components
    textArea = new JTextArea();
    openFileButton = new JButton("Open");
    saveFileButton = new JButton("Save");
    clearButton = new JButton("Clear");

    //create and register the listener object with
    //sources of events (the JButtons in this example)
    listener = new JFileChooserListener();
    openFileButton.addActionListener(listener);
    saveFileButton.addActionListener(listener);
    clearButton.addActionListener(listener);


    //arrange components in the window
    //Create a layout manager object and set this window's
    //layout manager to it
    textPanel = new JPanel();
    textPanel.setLayout(new GridLayout(1,2));
    textPanel.add(textArea);

    buttonPanel = new JPanel();
    buttonPanel.setLayout(new GridLayout(1,3,15,0));
    buttonPanel.add(openFileButton);
    buttonPanel.add(saveFileButton);
    buttonPanel.add(clearButton);
    this.setLayout(new GridLayout(3,1));



    //Add components to the container
    this.add(textPanel);
    this.add(buttonPanel);      


}//end of constructor
}//end of class

我还没有完成监听器类，但我认为这与仅显示 GUI 以确保布局正确没有任何关系？

我注意到，当我在同一行中声明和初始化时，我没有收到这四个错误。我初始化有问题吗？

Answer 1

我认为有几件事需要纠正

1. 构造函数名称与类名称不同。

2. 考虑到类方法之外的变量赋值:

   • 您必须同时声明并初始化变量。
   • 或者(更好的方法)在构造函数中声明并初始化。结账Java Variable declaration

3. 此外，还有一个小语法错误。 new 和构造函数名称之间应该有空格。

   public FileChooser () {
      //call superclass constructor
      super("File Chooser");
      fileChooser=fileChooser = new JFileChooser();
      fileFilter=new FileNameExtensionFilter("text file", "txt");
      fileChooser.setFileFilter(fileFilter);
   
     ...
      }
   

希望这有帮助!