Java实现简单记事本

代码实现：

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

public class NotepadDemo extends JFrame implements ActionListener {
    JTextArea inputText;
    JScrollPane pane;
    public NotepadDemo() {
        this.setTitle("Notepad");
        this.setSize(600, 400);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        Container contentPane = this.getContentPane();
        contentPane.setLayout(new BorderLayout(5,1));
        
        JMenuBar menuBar = new JMenuBar();
        JMenu menu = new JMenu("File");
        
        JMenuItem open=new JMenuItem("打开...");
        open.addActionListener(this);
        menu.add(open);
        JMenuItem save=new JMenuItem("存盘");
        save.addActionListener(this);
        menu.add(save);
        menu.addSeparator(); 
        JMenuItem item = new JMenuItem("退出");
        menu.add(item);
        item.addActionListener(this);

        menuBar.add(menu);
        
        this.setJMenuBar(menuBar);
        inputText=new JTextArea(100, 100);
        pane=new JScrollPane(inputText);
        contentPane.add(pane);
    }

    public static void main(String[] args) {
        JFrame frame = new NotepadDemo();
        frame.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent event) {
        String cmd = event.getActionCommand();
        if ("退出".equals(cmd)) {
            this.dispose();
        }
        if ("打开...".equals(cmd)) {
            File srcFile=null;
            JFileChooser fileChooser=new JFileChooser();
            int res=fileChooser.showOpenDialog(null);
            if(res==JFileChooser.APPROVE_OPTION) {
                srcFile=fileChooser.getSelectedFile();
            }
            try {
                InputStream is = new FileInputStream(srcFile);
                byte[] buffer = new byte[8*1024];
                int len;
                while ((len = is.read(buffer)) != -1) {
                    String text = new String(buffer, 0, len,"UTF-8");
                    inputText.append(text);
                }
                is.close();
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if ("存盘".equals(cmd)) {
            File destFile=null;
            JFileChooser fileChooser=new JFileChooser();
            int res = fileChooser.showSaveDialog(null);
            if (res == JFileChooser.APPROVE_OPTION) {
                destFile = fileChooser.getSelectedFile();
            } else {
                System.out.println("用户取消");
                return;
            }
            try {
                OutputStream os = new FileOutputStream(destFile);
                os.write(inputText.getText().getBytes("UTF-8"));
                os.close();
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}