Java/Design Pattern/Template Pattern
Template Method Pattern
<source lang="java">
//[C] 2002 Sun Microsystems, Inc.--- import java.io.Serializable; import java.util.ArrayList; import java.util.Iterator; public class RunTemplateMethodPattern {
public static void main(String [] arguments){
System.out.println("Example for the Template Method pattern");
System.out.println("This code demonstrates how the template method can");
System.out.println(" be used to define a variable implementation for a");
System.out.println(" common operation. In this case, the ProjectItem");
System.out.println(" abstract class defines the method getCostEstimate,");
System.out.println(" which is a combination of the cost for time and");
System.out.println(" materials. The two concrete subclasses used here,");
System.out.println(" Task and Deliverable, have different methods of");
System.out.println(" providing a cost estimate.");
System.out.println();
System.out.println("Creating a demo Task and Deliverable");
System.out.println();
Task primaryTask = new Task("Put a JVM on the moon", "Lunar mission as part of the JavaSpace program ;)", 240.0, 100.0);
primaryTask.addProjectItem(new Task("Establish ground control", "", 1000.0, 10.0));
primaryTask.addProjectItem(new Task("Train the Javanaughts", "", 80.0, 30.0));
Deliverable deliverableOne = new Deliverable("Lunar landing module", "Ask the local garage if they can make a few minor modifications to one of their cars", 2800, 40.0, 35.0);
System.out.println("Calculating the cost estimates using the Template Method, getCostEstimate.");
System.out.println();
System.out.println("Total cost estimate for: " + primaryTask);
System.out.println("\t" + primaryTask.getCostEstimate());
System.out.println();
System.out.println("Total cost estimate for: " + deliverableOne);
System.out.println("\t" + deliverableOne.getCostEstimate());
}
} abstract class ProjectItem implements Serializable{
private String name;
private String description;
private double rate;
public ProjectItem(){}
public ProjectItem(String newName, String newDescription, double newRate){
name = newName;
description = newDescription;
rate = newRate;
}
public void setName(String newName){ name = newName; }
public void setDescription(String newDescription){ description = newDescription; }
public void setRate(double newRate){ rate = newRate; }
public String getName(){ return name; }
public String getDescription(){ return description; }
public final double getCostEstimate(){
return getTimeRequired() * getRate() + getMaterialsCost();
}
public double getRate(){ return rate; }
public String toString(){ return getName(); }
public abstract double getTimeRequired();
public abstract double getMaterialsCost();
} class Task extends ProjectItem{
private ArrayList projectItems = new ArrayList();
private double taskTimeRequired;
public Task(){ }
public Task(String newName, String newDescription,
double newTaskTimeRequired, double newRate){
super(newName, newDescription, newRate);
taskTimeRequired = newTaskTimeRequired;
}
public void setTaskTimeRequired(double newTaskTimeRequired){ taskTimeRequired = newTaskTimeRequired; }
public void addProjectItem(ProjectItem element){
if (!projectItems.contains(element)){
projectItems.add(element);
}
}
public void removeProjectItem(ProjectItem element){
projectItems.remove(element);
}
public double getTaskTimeRequired(){ return taskTimeRequired; }
public Iterator getProjectItemIterator(){ return projectItems.iterator(); }
public double getMaterialsCost(){
double totalCost = 0;
Iterator items = getProjectItemIterator();
while (items.hasNext()){
totalCost += ((ProjectItem)items.next()).getMaterialsCost();
}
return totalCost;
}
public double getTimeRequired(){
double totalTime = taskTimeRequired;
Iterator items = getProjectItemIterator();
while (items.hasNext()){
totalTime += ((ProjectItem)items.next()).getTimeRequired();
}
return totalTime;
}
} class Deliverable extends ProjectItem{
private double materialsCost;
private double productionTime;
public Deliverable(){ }
public Deliverable(String newName, String newDescription,
double newMaterialsCost, double newProductionTime,
double newRate){
super(newName, newDescription, newRate);
materialsCost = newMaterialsCost;
productionTime = newProductionTime;
}
public void setMaterialsCost(double newCost){ materialsCost = newCost; }
public void setProductionTime(double newTime){ productionTime = newTime; }
public double getMaterialsCost(){ return materialsCost; }
public double getTimeRequired(){ return productionTime; }
}
</source>
Template pattern in Java
<source lang="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;
}
}
</source>
