triangle.java

源码为科学出版社出版的英文<java设计模式>(影印版)所用的所有例子程序

import java.awt.*;
public abstract class Triangle {
    private Point p1, p2, p3; 
    //---------------------------------------
    public Triangle(Point a, Point b, Point c) {
        //save
        p1 = a; p2 = b; p3 = c;
    }
    //---------------------------------------
    public void draw(Graphics g) {
        //This routine draws a general triangle
        drawLine(g, p1, p2);
        Point current = draw2ndLine(g, p2, p3);
        closeTriangle(g, current);
    }
    //---------------------------------------
    public void drawLine(Graphics g, Point a, Point b) {
        g.drawLine(a.x, a.y, b.x, b.y);
    }
    //---------------------------------------
    //this routine is the "Hook" that has to be implemented
    //for each triangle type.
    abstract public Point draw2ndLine(Graphics g, Point a, Point b);
    //---------------------------------------
    public void closeTriangle(Graphics g, Point c) {
        //draw back to first point
        g.drawLine(c.x, c.y, p1.x, p1.y);
    }

}