drawtest.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 drawtest;
	/** 
	 * 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.awt.*;
	import java.applet.*;
	import java.util.Vector;
	public class DrawTest extends Applet {			// 构造Applet小程序
    	public DrawTest() {							// 初始化窗口
		setLayout(new BorderLayout());
		DrawPanel dp = new DrawPanel();
		add("Center", dp);
		add("South",new DrawControls(dp));
		}
	    public boolean handleEvent(Event e) {		// 事件处理
			switch (e.id) {
			  case Event.WINDOW_DESTROY:
			    System.exit(0);
			    return true;
			  default:
			    return false;
			}
    	}
		public static void main(String args[]) {   // Application程序入口
		    Frame f = new Frame("画图程序");	   // 创建Application程序框架
			DrawTest drawTest = new DrawTest();
			drawTest.init();
			drawTest.start();
			f.add("Center", drawTest);
			f.resize(300, 300);
			f.show();
	    }
	}
	class DrawPanel extends Panel {					// 构造画板
	    public static final int LINES = 0;
	    public static final int POINTS = 1;
	    int	mode = LINES;							// 定义画线、画点模式
	    Vector lines = new Vector();				// 创建线段向量
	    Vector colors = new Vector();				// 创建颜色向量
	    int x1,y1;	int x2,y2;	int xl, yl;			// 定义坐标变量
	    public DrawPanel() {
			setBackground(Color.white);
	    }
	    public void setDrawMode(int mode) {			// 设置画点、画线模式
			switch (mode) {
			  case LINES:
			  case POINTS:
			    this.mode = mode;
			    break;
			  default:
			    throw new IllegalArgumentException();
			}
    	}
	    public boolean handleEvent(Event e) {		// 鼠标按键、放键事件处理
			switch (e.id) {
			  case Event.MOUSE_DOWN:				// 鼠标按键
			    switch (mode) {
			      case LINES:						// 画线处理
					x1 = e.x;	y1 = e.y;	x2 = -1;
					break;
		      	  case POINTS:						// 画点处理
			      default:
					colors.addElement(getForeground());
					lines.addElement(new Rectangle(e.x, e.y, -1, -1));
					x1 = e.x;	y1 = e.y;
					repaint();
					break;
			    }
			    return true;
			  case Event.MOUSE_UP:					// 鼠标放键
			    switch (mode) {
			      case LINES:						// 画线处理
				colors.addElement(getForeground());
				lines.addElement(new Rectangle(x1, y1, e.x, e.y));
				x2 = xl = -1;
				break;
			      case POINTS:						// 画点处理
			      default:
					break;
			    }
			    repaint();							// 刷新屏幕
			    return true;
			  case Event.MOUSE_DRAG:				// 鼠标拖动
			    switch (mode) {
			      case LINES:						// 画线处理
					xl = x2;	yl = y2;
					x2 = e.x;	y2 = e.y;
					break;
			      case POINTS:						// 画点处理
			      default:
					colors.addElement(getForeground());
					lines.addElement(new Rectangle(x1, y1, e.x, e.y));
					x1 = e.x;	y1 = e.y;
					break;
			    }
			    repaint();
			    return true;
			  case Event.WINDOW_DESTROY:			// 结束程序
			    System.exit(0);
			    return true;
			  default:
			    return false;
			}
	    }
	    public void paint(Graphics g) {				// 画线（LINES）
			int np = lines.size();
			g.setColor(getForeground());
			g.setPaintMode();
			for (int i=0; i < np; i++) {
			    Rectangle p = (Rectangle)lines.elementAt(i);
			    g.setColor((Color)colors.elementAt(i));
			    if (p.width != -1) {
					g.drawLine(p.x, p.y, p.width, p.height);
			    } 
				else {
					g.drawLine(p.x, p.y, p.x, p.y);
				}
			}
			if (mode == LINES) {
			    g.setXORMode(getBackground());
			    if (xl != -1) {
					g.drawLine(x1, y1, xl, yl);		// 画线
			    }
			    g.setColor(getForeground());
			    g.setPaintMode();
			    if (x2 != -1) {
				g.drawLine(x1, y1, x2, y2);			// 画线
			    }
			}
	    }
	}
	class DrawControls extends Panel {				// 构造画图控件（组件）
    	DrawPanel target;
	    public DrawControls(DrawPanel target) {
			this.target = target;
			setLayout(new FlowLayout());
			setBackground(Color.lightGray);
			target.setForeground(Color.red);
			CheckboxGroup group = new CheckboxGroup();
			Checkbox b;
			add(b = new Checkbox(null, group, false));
			b.setBackground(Color.red);
			add(b = new Checkbox(null, group, false));
			b.setBackground(Color.green);
			add(b = new Checkbox(null, group, false));
			b.setBackground(Color.blue);
			add(b = new Checkbox(null, group, false));
			b.setBackground(Color.pink);
			add(b = new Checkbox(null, group, false));
			b.setBackground(Color.orange);
			add(b = new Checkbox(null, group, true));
			b.setBackground(Color.black);
			target.setForeground(b.getForeground());
			Choice shapes = new Choice();
			shapes.addItem("LINES");
			shapes.addItem("POINTS");
			shapes.setBackground(Color.lightGray);
			add(shapes);
	    }
	    public void paint(Graphics g) {
			Rectangle r = bounds();
			g.setColor(Color.lightGray);
			g.draw3DRect(0, 0, r.width, r.height, false);
	    }
	    public boolean action(Event e, Object arg) {	// 响应画图控件事件
			if (e.target instanceof Checkbox) {			// 选择画线、点颜色
			    target.setForeground(((Component)e.target).getBackground());
			} 
			else 
				if (e.target instanceof Choice) {
	    			String choice = (String)arg;
				    if (choice.equals("LINES")) {		// 选择画线
						target.setDrawMode(DrawPanel.LINES);
			    	} 
					else 
						if (choice.equals("POINTS")) {	// 选择画点
							target.setDrawMode(DrawPanel.POINTS);
				    	}
				}
			return true;
	    }
	}