JAVA记事本代码，老师让做成ppt讲解，求大神指出里面的重点和需要讲解的地方，最好详细点

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　　import java.awt.*;import java.awt.event.*;import java.io.*;import javax.swing.*;public class MyNotepad implements ActionListener{private JFrame frame=new JFrame("新记事本");private JTextArea jta=new JTextArea();private String result="";private boolean flag=true;private File f;private JButton jb=new JButton("开始");private JTextField jtf=new JTextField(15);private JTextField jt=new JTextField(15);private JButton jbt=new JButton("替换为");private JButton jba=new JButton("全部替换");private Icon ic=new ImageIcon("D:\\java课堂笔记\\GUI\\11.gif");private String value;private int start=0;private JFrame jf=new JFrame("查找");private JFrame jfc=new JFrame("替换");@Overridepublic void actionPerformed(ActionEvent e) {String m=e.getActionCommand();if("新建".equals(m)){if(!(frame.getTitle().equals("新记事本"))){if(!flag){write();newNew();}else{JFileChooser jfc=new JFileChooser("D:\\java课堂笔记"); int returnVal = jfc.showDialog(null,"保存为"); if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性 f=jfc.getSelectedFile(); flag=false;write(); }}}else if(!(jta.getText().isEmpty())){JFileChooser jfc=new JFileChooser("D:\\java课堂笔记"); int returnVal = jfc.showDialog(null,"保存为"); if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性 f=jfc.getSelectedFile(); flag=false;write();newNew(); }}else{newNew();}}else if("打开".equals(m)){JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");jfc.setDialogType(JFileChooser.OPEN_DIALOG); int returnVal = jfc.showOpenDialog(null); if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性f=jfc.getSelectedFile();frame.setTitle(f.getName());result=read();flag=false;value=result;jta.setText(result); }}else if("保存".equals(m)){JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");if(flag){ int returnVal = jfc.showDialog(null,"保存为"); if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性 f=jfc.getSelectedFile(); flag=false;write(); }}else{write();}}else if("另存".equals(m)){JFileChooser jfc=new JFileChooser("D:\\java课堂笔记"); int returnVal = jfc.showDialog(null,"另存"); if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性 f=jfc.getSelectedFile();write(); }}else if("退出".equals(m)){System.exit(0);}else if("撤销".equals(m)){jta.setText(value);}else if("剪切".equals(m)){value=jta.getText();jta.cut();}else if("复制".equals(m)){jta.copy();}else if("粘贴".equals(m)){value=jta.getText();jta.paste();}else if("删除".equals(m)){value=jta.getText();jta.replaceSelection(null);}else if("全选".equals(m)){jta.selectAll();}else if("查找".equals(m)){value=jta.getText();jf.add(jtf,BorderLayout.CENTER);jf.add(jb,BorderLayout.SOUTH);jf.setLocation(300,300);jf.pack();jf.setVisible(true);jf.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);}else if("替换".equals(m)){value=jta.getText();GridLayout gl=new GridLayout(3,3);JLabel jl1=new JLabel("查找内容:");JLabel jl2=new JLabel("替换为:");jfc.setLayout(gl);jfc.add(jl1);jfc.add(jtf);jfc.add(jb);jfc.add(jl2);jfc.add(jt);jfc.add(jbt);JLabel jl3=new JLabel();JLabel jl4=new JLabel();jfc.add(jl3);jfc.add(jl4);jfc.add(jba);jfc.setLocation(300,300);jfc.pack();jfc.setVisible(true);jfc.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);}else if("版本".equals(m)){JDialog jd=new JDialog(frame,"关于对话框");jd.setSize(200,200);JLabel l=new JLabel("哈哈哈哈哈哈哈哈哈哈呵呵呵呵呵呵呵呵呵呵呵呵呵");jd.add(l,BorderLayout.CENTER);jd.setLocation(100,200);jd.setSize(300,300);jd.setVisible(true);//jd.pack();jd.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);}else if("开始".equals(m)||"下一个".equals(m)){ String temp=jtf.getText();int s=value.indexOf(temp,start);if(value.indexOf(temp,start)!=-1){jta.setSelectionStart(s);jta.setSelectionEnd(s+temp.length());jta.setSelectedTextColor(Color.GREEN);start=s+1;jb.setText("下一个");//value=value.substring(s+temp.length());//不能截取字串}else {JOptionPane.showMessageDialog(jf, "查找完毕!", "提示", 0, ic);jf.dispose();}}else if("替换为".equals(m)){String temp=jtf.getText();int s=value.indexOf(temp,start);if(value.indexOf(temp,start)!=-1){jta.setSelectionStart(s);jta.setSelectionEnd(s+temp.length());jta.setSelectedTextColor(Color.GREEN);start=s+1;jta.replaceSelection(jt.getText());}else {JOptionPane.showMessageDialog(jf, "查找完毕!", "提示", 0, ic);jf.dispose();}}else if("全部替换".equals(m)){String temp=jta.getText();temp=temp.replaceAll(jtf.getText(), jt.getText());jta.setText(temp);}}public String read(){String temp="";try {FileInputStream fis = new FileInputStream(f.getAbsolutePath());byte[] b=new byte[1024];while(true){int num=fis.read(b);if(num==-1)break;temp=temp+new String(b,0,num);}fis.close();} catch (Exception e1) {e1.printStackTrace();}return temp;}public void write(){try {FileOutputStream fos=new FileOutputStream(f);fos.write(jta.getText().getBytes());fos.close();} catch (Exception e) {e.printStackTrace();}}public void newNew(){frame.dispose();new MyNotepad();flag=true;}public MyNotepad(){JMenuBar jmb=new JMenuBar();String[] menuLab={"文件","编辑","帮助"};String[][] menuItemLab={{"新建","打开","保存","另存","退出"},{"撤销","剪切","复制","粘贴","删除","全选","查找","替换"},{"版本"}};for(int i=0;i<menuLab.length;i++){JMenu menu=new JMenu(menuLab[i]);jmb.add(menu);for(int j=0;j<menuItemLab[i].length;j++){JMenuItem jmi=new JMenuItem(menuItemLab[i][j]);menu.add(jmi);jmi.addActionListener(this);}}frame.setJMenuBar(jmb);jta.setLineWrap(true);//自动换行JScrollPane jsp=new JScrollPane(jta);//滚动窗口面板frame.add(jsp);jb.addActionListener(this);jbt.addActionListener(this);jba.addActionListener(this);frame.setLocation(200,50);frame.setSize(620,660);frame.setVisible(true);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}public static void main(String[] args) {new MyNotepad();}}