ticker.java

java对文件进行操作的例子

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.net.*;
import java.io.*;

public class Ticker extends Applet implements Runnable{

	//设定全局参数
	private Thread m_thread;
	private Image m_imgBuffer = null;
	private int y_pos = 0;		// 纵向位置
	private int cur_news = 0;	// 当前news项目
	private int cur_pos = 0;	// 当前鼠标光标所在位置
	private boolean pause = false;	// 是否暂停
	private boolean m_over = false;	// 是否鼠标掠过
	private Vector news = new Vector(); //包含显示的文字
	private Vector urls = new Vector(); //包含相关的URL

	//设定默认参数
	private int size = 10;
	private Font ft = new Font("TimesRoman",Font.PLAIN,size);
	private String filename = "news.txt";
	private String target = "_new";
	private int height;
	private int xmargin = 10;
	private int ymargin = 0;
	private Color irect = new Color(8388736);
	private Color orect = new Color(0);
	private Color ntext = new Color(0);
	private Color htext = new Color(16711680);
	private int speed = 100;
	
	//初始化
	public void init(){
		//获取小应用程序给定的参数
		String param;
		param = getParameter("size");
		if (param != null) size = Integer.parseInt(param);
		param = getParameter("font");
		if (param != null) ft = new Font(param,Font.PLAIN,size);
		param = getParameter("target");
		if (param != null) target = param;
		param = getParameter("xmargin");
		if (param != null) xmargin = Integer.parseInt(param);
		param = getParameter("ymargin");
		if (param != null) ymargin = Integer.parseInt(param);
		param = getParameter("irect");
		if (param != null) irect = new Color(Integer.parseInt(param,16));
		param = getParameter("orect");
		if (param != null) orect = new Color(Integer.parseInt(param,16));
		param = getParameter("ntext");
		if (param != null) ntext = new Color(Integer.parseInt(param,16));
		param = getParameter("htext");
		if (param != null) htext = new Color(Integer.parseInt(param,16));
		param = getParameter("filename");
		if (param != null) filename = param;
		param = getParameter("speed");
		if (param != null) speed = Integer.parseInt(param);

		setFont(ft);
		FontMetrics fm = getFontMetrics(ft);
		height = fm.getAscent() + fm.getDescent();
		if (height > ymargin) ymargin = height;	//设定的纵向边框空白处不能太小

		//读取news文件中的信息
		readFile();
	}
	//鼠标移入
	public boolean mouseEnter(Event e, int x, int y){
		stop();
		m_over = true;
		cur_pos = e.y;
		repaint();
		return true;
	}
	//鼠标移出
	public boolean mouseExit(Event e, int x, int y){
		start();
		m_over = false;
		repaint();
		return true;
	}
	//鼠标移动
	public boolean mouseMove(Event e, int x, int y){
		cur_pos = e.y;
		m_over = true;
		repaint();
		return true;
	}
	//单击鼠标
	public boolean mouseDown(Event e, int x, int y){
		if (urls.elementAt(cur_news) instanceof URL){
			URL myURL = (URL) urls.elementAt(cur_news);
			getAppletContext().showDocument(myURL,getParameter("target"));
		}
		return true;
	}

	//本函数实现读取文件
	private void readFile()
	{
		String line;
		try{
			URL url = new URL(getDocumentBase(), filename);
			try{	//读取文件
				BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
				do{
					line = in.readLine();
					if (line != null){
						try{
							StringTokenizer st = new StringTokenizer(line, "|");
							news.addElement(st.nextToken());	//获取要显示的文字
							if (st.hasMoreTokens()){	//得到url
								urls.addElement(new URL(getDocumentBase(), st.nextToken()));
							}
							else{	// 如果没有url
								urls.addElement("nourl");
							}
						}catch (NoSuchElementException nsee){}	//抛出异常

					}
				}while (line != null);
			}
			catch (IOException e){
				news.addElement("Could not open news feed file.");
				urls.addElement("nourl");
				System.err.println("Could not open news feed file.");
			}
		}catch (MalformedURLException e){}
	}

	public void paint(Graphics g){
		if (m_imgBuffer == null){	//双缓冲
			m_imgBuffer = createImage(size().width, size().height);
			render(g);	//显示
		}
		g.drawImage(m_imgBuffer, 0, 0, null);
	}

	public void update(Graphics g){
		render(g);
		paint(g);
	}

	//本函数实现显示
	public void render(Graphics g)
	{
		//画背景区域
		g = m_imgBuffer.getGraphics();
		g.setColor(orect);
		g.fillRect(0, 0, size().width, size().height);
		g.setColor(irect);
		g.fillRect(xmargin, ymargin, size().width - 2 * xmargin, size().height - 2 * ymargin);
		g.setColor(ntext);

		FontMetrics fm = getFontMetrics(ft);	//计算字符宽度
		boolean reset = false;	//重新设置y_pos的值
		int y = 0;
		String s = "";

		while (y + y_pos < size().height){
			//计算news中每个项目的位置
			for (int i = 0; i < news.size(); i++){
				if (m_over){	//如果鼠标的光标移动到文字上
					int b1 = y_pos + 14;	//news边框的顶部
					int b2 = y_pos + 14;	//news边框的底部
					//寻找当前的news项目，并将其突出显示
					while (b2 < size().height - height){
						for (int j = 0; j < news.size(); j++){
							b1 = b2;	//设置顶部边框
							StringTokenizer st = new StringTokenizer((String) news.elementAt(j)," ",false);
							String t = "";
							while (st.hasMoreTokens()){
								s = "";
								while (fm.stringWidth(s + t) < size().width - 2 * xmargin - 5 && st.hasMoreTokens()){
									if (!t.equals("")) s += t + " ";
									t = st.nextToken();
								}

								if (!st.hasMoreTokens() && fm.stringWidth(s + t) > size().width - 2 * xmargin - 5){
									b2 += 2 * height;
								}
								else{
									b2 += height;
								}
							}
							if (cur_pos > b1 && cur_pos < b2){//搜寻当前的news
								cur_news = j;
							}
							b2 += 20;	//计算底部边框
						}
					}
					//突出显示项目
					if (i == cur_news && (urls.elementAt(i) instanceof URL)) g.setColor(htext);
					else g.setColor(ntext);
				}

				//当新项目出现时，使滚动暂停
				if (y_pos + y == 3){
					pause = true;
				}

				//显示文字
				String t = "";
				StringTokenizer st = new StringTokenizer((String) news.elementAt(i)," ",false);
				while (st.hasMoreTokens()){
					s = "";
					while (fm.stringWidth(s + t) < size().width - 2 * xmargin - 5 && st.hasMoreTokens()){
						if (!t.equals("")) s += t + " ";
						t = st.nextToken();
					}

					y += height;

					if (st.hasMoreTokens()){
						if ( y + y_pos > ymargin - height && y + y_pos < size().height - ymargin - 2 * height){
							g.drawString(s, xmargin + 2, y + y_pos + ymargin);
						}
					}
					else{	//对最后一行做特殊处理
						if (fm.stringWidth(s + t) > size().width - 2 * xmargin - 5){
							//如果没有足够的空间，在另一行显示
							if ( y + y_pos > ymargin - height && y + y_pos < size().height - ymargin - 2 * height){
								g.drawString(s, xmargin + 2, y + y_pos + ymargin);
							}
							y += height;
							if ( y + y_pos > ymargin - height && y + y_pos < size().height - ymargin - 2 * height){
								g.drawString(t, xmargin + 2, y + y_pos + ymargin);
							}
						}
						else{	//否则在同一行显示
							if ( y + y_pos > ymargin - height && y + y_pos < size().height - ymargin - 2 * height){
								g.drawString(s + t, xmargin + 2, y + y_pos + ymargin);
							}
						}
					}
				}
				y += 20;
			}
			if (y + y_pos < 0) reset = true;
		}
		if (reset) y_pos = 0;	//重新设置滚动器的纵向位置
	}

	public void start(){
		m_thread = new Thread(this);
		m_thread.start();
	}

	public void stop(){
		m_thread.stop();
	}

	public void run(){
		try{
			while(true){
				if (pause){	//当新的项目出现时，暂停
					m_thread.sleep(4000);
					pause = false;
				}
				m_thread.sleep(speed);
				if (!m_over) y_pos--;	//实现滚动
				repaint();
			}
		}
		catch (InterruptedException e){}
	}
}