rollingmessage.java

递归子程序法：对应每个非终结符语法单元编一个独立的处理过程（或子程序）。语法分析从读入第一个单词开始

	package rollingmessage;
	/** 
	 * Java语言实验参考程序
	 * Company 北京师范大学计算机系
 
	 * @author 孙一林
	 * @version 1.0
	 */
	import java.applet.*;
	import java.awt.*;
	import java.awt.Color;
	import java.awt.Font;
	import java.awt.Graphics;
	public class RollingMessage extends Applet implements Runnable {
		Thread runThread;
		String s = "你好，欢迎浏览!";				// 定义文字
		int s_length = s.length();					// 获取字符串长度
		int x_character = 0;						// 显示到第几个字符
		Font wordFont = new Font("宋体" , Font.BOLD , 50);
		public void start() {
			if( runThread == null ){
				runThread = new Thread(this);
				runThread.start();					// 启动线程
			}
		}
		public void stop() {
			if( runThread != null ){
				runThread.stop();					// 停止线程
				runThread = null;
			}
		}
		public void run() {
			while(true) {
				if ( x_character++ > s_length )		// 显示字符计数加1
					x_character = 0;				// 显示字符计数清0
				repaint ();							// 刷新显示
				try {
					Thread.sleep(300);				// 线程休眠
				} 
				catch ( InterruptedException e ) {}
			}
		}
		public void paint ( Graphics g ) {			// 显示文字
			g.setFont (wordFont);
			g.setColor (Color.red);
			g.drawString ( s.substring(0,x_character), 8, 50 );
		}
	}