Template pattern in Java : Template Pattern « Design Pattern « Java

1. Java
2. Design Pattern
3. Template Pattern

Template pattern in Java

/*
The Design Patterns Java Companion

Copyright (C) 1998, by James W. Cooper

IBM Thomas J. Watson Research Center

*/

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.Vector;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class TriangleDrawing extends JFrame {
  stdTriangle t, t1;

  IsocelesTriangle it;

  public TriangleDrawing() {
    super("Draw triangles");
    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });

    TPanel tp = new TPanel();
    t = new stdTriangle(new Point(10, 10), new Point(150, 50), new Point(
        100, 75));
    it = new IsocelesTriangle(new Point(150, 100), new Point(240, 40),
        new Point(175, 150));
    t1 = new stdTriangle(new Point(150, 100), new Point(240, 40),
        new Point(175, 150));
    tp.addTriangle(t);
    tp.addTriangle(it);
    // tp.addTriangle(t1);

    getContentPane().add(tp);
    setSize(300, 200);
    setBackground(Color.white);
    setVisible(true);
  }

  public static void main(String[] arg) {
    new TriangleDrawing();
  }
}

class TPanel extends JPanel {
  Vector triangles;

  public TPanel() {
    triangles = new Vector();
  }

  public void addTriangle(Triangle t) {
    triangles.addElement(t);
  }

  public void paint(Graphics g) {
    for (int i = 0; i < triangles.size(); i++) {
      Triangle tngl = (Triangle) triangles.elementAt(i);
      tngl.draw(g);
    }
  }
}

abstract class Triangle {
  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);
  }

}

class stdTriangle extends Triangle {
  public stdTriangle(Point a, Point b, Point c) {
    super(a, b, c);
  }

  public Point draw2ndLine(Graphics g, Point a, Point b) {
    g.drawLine(a.x, a.y, b.x, b.y);
    return b;
  }
}

class IsocelesTriangle extends Triangle {
  Point newc;

  int newcx, newcy;

  int incr;

  public IsocelesTriangle(Point a, Point b, Point c) {
    super(a, b, c);
    double dx1 = b.x - a.x;
    double dy1 = b.y - a.y;
    double dx2 = c.x - b.x;
    double dy2 = c.y - b.y;

    double side1 = calcSide(dx1, dy1);
    double side2 = calcSide(dx2, dy2);

    if (side2 < side1)
      incr = -1;
    else
      incr = 1;

    double slope = dy2 / dx2;
    double intercept = c.y - slope * c.x;

    //move point c so that this is an isoceles triangle
    newcx = c.x;
    newcy = c.y;
    while (Math.abs(side1 - side2) > 1) {
      newcx += incr; //iterate a pixel at a time until close
      newcy = (int) (slope * newcx + intercept);
      dx2 = newcx - b.x;
      dy2 = newcy - b.y;
      side2 = calcSide(dx2, dy2);
    }
    newc = new Point(newcx, newcy);
  }

  //calculate length of side
  private double calcSide(double dx, double dy) {
    return Math.sqrt(dx * dx + dy * dy);
  }

  //draws 2nd line using saved new point
  public Point draw2ndLine(Graphics g, Point b, Point c) {
    g.drawLine(b.x, b.y, newc.x, newc.y);
    return newc;
  }
}

           
       

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