Java学习笔记（五）

作业1：将指定目录下的所有文件显示到列表框（JList）组件中。

代码如下：

import java.awt.;

import java.awt.event.;

import javax.swing.;

import javax.swing.event.;

import javax.swing.border.*;

import java.util.List;

import java.util.ArrayList;

import java.io.*;

public class wj extends JFrame

implements ChangeListener, ActionListener

{

private static final String VERSION = "Version 1.0";

private static final String WENJ_DIR = "文件";

private JList fileList;
private SoundEngine player;
public static void main(String[] args)
{
    wj gui = new wj();
}
public wj()
{
    super("文件");
    player = new SoundEngine();
    String[] FileNames = findFiles(WENJ_DIR, null);
    makeFrame(FileNames);
}
private void quit()
{
    System.exit(0);
}
private void showAbout()
{
    JOptionPane.showMessageDialog(this,
                "文件\n" + VERSION,
                "About 文件",
                JOptionPane.INFORMATION_MESSAGE);
}
private String[] findFiles(String dirName, String suffix)
{
    File dir = new File(dirName);
    if(dir.isDirectory()) {
        String[] allFiles = dir.list();
        if(suffix == null) {
            return allFiles;
        }
        else {
            List<String> selected = new ArrayList<String>();
            for(String filename : allFiles) {
                if(filename.endsWith(suffix)) {
                    selected.add(filename);
                }
            }
            return selected.toArray(new String[selected.size()]);
        }
    }
    else {
        System.out.println("Error: " + dirName + " must be a directory");
        return null;
    }
}
public void stateChanged(ChangeEvent evt)
{
}
//添加监听器
public void actionPerformed(ActionEvent evt)
{
    JComboBox cb = (JComboBox)evt.getSource();
    String format = (String)cb.getSelectedItem();
    if(format.equals("all")) {
        format = null;
    }
    fileList.setListData(findFiles(WENJ_DIR, format));
}
private void makeFrame(String[] Files)
{
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    JPanel contentPane = (JPanel)getContentPane();
    contentPane.setBorder(new EmptyBorder(6, 10, 10, 10));
    makeMenuBar();
    contentPane.setLayout(new BorderLayout(8, 8));
    JPanel leftPane = new JPanel();
    {
        leftPane.setLayout(new BorderLayout(8, 8));
        String[] formats = { "all", ".doc", ".png", ".mp3" };
        JComboBox formatList = new JComboBox(formats);
        formatList.addActionListener(this);
        leftPane.add(formatList, BorderLayout.NORTH);
        fileList = new JList(Files);
        fileList.setForeground(new Color(140,171,226));
        fileList.setBackground(new Color(0,0,0));
        fileList.setSelectionBackground(new Color(87,49,134));
        fileList.setSelectionForeground(new Color(140,171,226));
        JScrollPane scrollPane = new JScrollPane(fileList);
        scrollPane.setColumnHeaderView(new JLabel("wenj files"));
        leftPane.add(scrollPane, BorderLayout.CENTER);
    }
    contentPane.add(leftPane, BorderLayout.CENTER);
    pack();
    Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
    setLocation(d.width/2 - getWidth()/2, d.height/2 - getHeight()/2);
    setVisible(true);
}

//设置菜单项

private void makeMenuBar()

{

final int SHORTCUT_MASK =

Toolkit.getDefaultToolkit().getMenuShortcutKeyMask();

    JMenuBar menubar = new JMenuBar();
    setJMenuBar(menubar);
    JMenu menu;
    JMenuItem item;
    menu = new JMenu("File");
    menubar.add(menu);
    item = new JMenuItem("Quit");
        item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, SHORTCUT_MASK));
        item.addActionListener(new ActionListener() {
                           public void actionPerformed(ActionEvent e) { quit(); }
                       });
    menu.add(item);
    menu = new JMenu("Help");
    menubar.add(menu);
    item = new JMenuItem("About ...");
        item.addActionListener(new ActionListener() {
                           public void actionPerformed(ActionEvent e) { showAbout(); }
                       });
    menu.add(item);
}

}

界面图：

作业2：将游戏中最高纪录的玩家信息输出。

方法：这个可以利用seek()方法跳转指针和getFilePointer()方法来获取当前指针位置实现。

代码如下：

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

public class TestRandomAccessFile{

private File file;

public static void main(String[] args){

TestRandomAccessFile traf = new TestRandomAccessFile();

traf.init();

traf.record("Adom",80);

traf.listAllRecords();

}
public void record(String record_breaker, int times){
	try{
		RandomAccessFile raf = new RandomAccessFile(file,"rw");
		boolean flag = false;
		while(raf.getFilePointer() < raf.length()){
			String name = raf.readUTF();
			                 long prior = raf.getFilePointer();
			                 if (record_breaker.equalsIgnoreCase(name)) {
			                     flag = true;
			                     //比较传递进来的数与之前数的大小
			                     if (raf.readInt() < times) {
			                        //利用seek()方法跳转到prior的位置
			                         raf.seek(prior);
			                         raf.writeInt(times);
			                         break;
			                     }
			                 } else {
			                     raf.skipBytes(4);
			                 }
			             }
		if(!flag){
			raf.writeUTF(record_breaker);
			raf.writeInt(times);
		}
		raf.close();
	}catch(Exception e){
		e.printStackTrace();
	}
}
public void init(){
	if(file == null){
		file = new File("record.txt");
		try{
			file.createNewFile();
		}catch(IOException e){
			e.printStackTrace();
		}
	}
}
public void listAllRecords(){
	try{
		RandomAccessFile raf = new RandomAccessFile(file,"r");
		while(raf.getFilePointer() < raf.length()){
			String name = raf.readUTF();
			int times = raf.readInt();
			System.out.println("name:" + name + "\trecord:" + times);
		}
		raf.close();
	}catch(Exception e){
		e.printStackTrace();
	}
}

}

界面图：

原来的程序效果图：

添加记录后的程序效果图：