Java graphical interface development simple notepad

Content
After learning Java events, I wrote a very simple notepad myself. It uses MenuBar, Menu, MenuITem, and other controls, and events include ActionListener and KeyListener.

The code is as follows:3import java.io. 
/* 
 * package com.package 
 * Function: Development of a simple notepad, which can save files, open files, and exit the notepad 
 */ 
author: ywq*import java.io. 
import javax.swing.*import java.io. 
import java.awt.*import java.io. 
import java.awt.event.*import java.io. 
; 
  //public class MenuText { 
  Define components: 
  JFrame f;  //MenuBar mb; 
  Menu mu;    //Menu 
  JTextArea jta; 
  MenuItem openItem, saveItem, closeItem;  //Submenu 
  FileDialog openDia,saveDia;  //Pop-up save and open boxes 
  File file; 
  //Constructor 
  public MenuText() 
  { 
    //Call the initialization function 
    init(); 
  } 
  //Perform initialization operations on the components 
  public void init() 
  { 
    f=new JFrame("简易记事本"); 
    mb=new MenuBar(); 
    mu=new Menu("文件"); 
    openItem=new MenuItem("打开"); 
    saveItem=new MenuItem("保存"); 
    closeItem=new MenuItem("Exit"); 
    jta=new JTextArea(); 
    f.add(jta); 
    //Add 
    mu.add(openItem); 
    mu.add(saveItem); 
    mu.add(closeItem); 
    mb.add(mu); 
    f.setMenuBar(mb); 
    openDia=new FileDialog(f, "Open", FileDialog.LOAD); 
    saveDia=new FileDialog(f, "Save", FileDialog.SAVE); 
    //Set JFrame properties 
    f.setBounds(200, 300, 500, 400); 
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    f.setVisible(true); 
    //Call the event function 
    event(); 
  } 
  //Event function, to handle the event 
  public void event() 
  { 
    //Open options 
    openItem.addActionListener(new ActionListener()) 
    { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
      //Call the method to open the file 
        openFile(); 
      } 
    }); 
    //Save options 
    saveItem.addActionListener(new ActionListener()) 
    { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
      //Call the method to save the file. 
       saveFile();   
      } 
    }); 
    //Add an event to the text area, that is, press Ctrl+S can be saved 
    //Because there are many ways to listen to keyboard events, and we only need one of them, we can use the adapter KeyAdapter, 
    //Thus, only one method needs to be implemented 
    jta.addKeyListener(new KeyAdapter()) 
    { 
      //Key press method 
      public void keyPressed(KeyEvent e){ 
        if(e.isControlDown() && e.getKeyCode() == KeyEvent.VK_S) 
        { 
          //Call the method to save the file. 
           saveFile();   
          //JOptionPane.showMessageDialog(null, "Right!"); 
        } 
      } 
    }); 
    //Close options 
    closeItem.addActionListener(new ActionListener()) 
    { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
        //Exit the system 
        System.exit(0); 
      } 
    }); 
  } 
  //method to open text 
  public void openFile() 
  { 
    openDia.setVisible(true); //set it to be displayed 
    //get the path and file name 
    String dirPath = openDia.getDirectory(); 
    String fileName = openDia.getFile(); 
    //prevent error reporting when cancel is clicked 
    if(dirPath == null || fileName == null) 
      return ; 
    jta.setText(""); //clear the text area 
    file = new File(dirPath, fileName); //create a file object 
    //read data line by line, display in text area 
    try 
    { 
      BufferedReader br = new BufferedReader(new FileReader(file)); 
      String line = null; 
      while((line = br.readLine()) != null) 
      { 
        jta.append(line+"\r\n"); 
      } 
      br.close(); 
    } 
    catch (IOException ex) 
    { 
      throw new RuntimeException("read failed"); 
    } 
  } 
  //method to save text. 
  public void saveFile() 
  { 
    //first check if the file exists 
    if(file == null) 
    { 
      saveDia.setVisible(true); 
      String dirPath = saveDia.getDirectory(); 
      String fileName = saveDia.getFile(); 
      //prevent error reporting when cancel is clicked 
      if(dirPath == null || fileName == null) 
        return ;   
      //Since the file does not exist, a file object needs to be created 
      file = new File(dirPath, fileName);        
    } 
    //write data to file 
    try { 
      BufferedWriter bw = new BufferedWriter(new FileWriter(file)); 
      String info = jta.getText(); //get the text area information 
      bw.write(info); //writing operation 
      bw.flush(); 
      bw.close(); 
    } catch (IOException e1) { 
      throw new RuntimeException(); 
    }     
  } 
  public static void main(String[] args) { 
      //Create an object 
    new MenuText(); 
  } 
} 

The running result is shown in the figure below:

The functions implemented by this program include:

(1) can open a file and can edit it.

(2) can save the edited file.

(3) can use Ctrl+) save the text with S

(4) you can click closeItem to exit the program.

InImplement the function3When adding a KeyListener to the text area, it uses the adapter KeyAdapter to implement the listening. But now what is needed is a combination listening, that is, when both Ctrl and S are pressed, the save operation will be triggered.

The Java API provides the corresponding method for combination listening.

Find the direct superclass of the KeyEvent class, which is the InputEvent class. As shown in the figure:

Check the methods in the InputEvent class, as shown below:

　 　 　 The object e of the KeyEvent class, which is a subclass of the InputEvent class, can directly call the above method to make a judgment. The isControlDown() method is used to determine whether the control key is pressed. As shown in the program if(e.isControlDown() && e.getKeyCode() == KeyEvent.VK_S) the combination judgment is implemented.

That's all for this article. Hope it helps everyone's learning and also hope everyone will support the Niyao tutorial.

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