Using Template Method Design Pattern In Java
Today, I will discuss another very useful design pattern named the Template Method Design Pattern. Read on to find out more!
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Join For FreeToday, I will discuss another very useful design pattern named the Template Method Design Pattern.
Template Method Design Pattern
- The Template Method pattern is one of the behavioral design patterns identified by Gamma et al. in the book Design Patterns.
- The Template Method pattern provides a method in a super-class, usually an abstract super-class, and defines the skeleton of an operation in terms of several high-level steps.
- Generally, these steps are implemented by additional helper methods in the same class as the template method.
- The helper methods may be either created as an abstract method, for which sub-classes are required to provide concrete implementations, or hook methods, which have empty bodies in the super-class.
- The Template Method design pattern is used to define an algorithm as a skeleton of operations and leave the details to be implemented by the child classes.
- In this way of implementation, the overall structure and sequence of the algorithm are preserved by the parent class.
- The Template Method pattern defines the sequential steps to execute a multi-step algorithm. We can provide a default implementation as well.
- In the Template Method pattern, we define a preset structure method called template method which consists of steps.
- These steps can be created as an abstract method which will be implemented by its sub-classes.
- In the Template Method pattern, an abstract class exposes defined way(s)/template(s) to execute its methods.
- The template method uses and defines the sequence of steps to perform the algorithm.
Let's take an example to understand it better.
Car Manufacturing Example Using Template Method Design Pattern
I am using the same example I used for explaining the Builder Design Pattern to help you understand the difference between both.
First, we define an abstract class to represent a car manufacturing template. Here's the code for CarTemplate class:
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package org.trishinfotech.template;
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public abstract class CarTemplate {
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protected String chassis;
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protected String body;
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protected String paint;
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protected String interior;
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public CarTemplate() {
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super();
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}
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// steps
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public abstract void fixChassis();
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public abstract void fixBody();
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public abstract void paint();
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public abstract void fixInterior();
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// template method
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public void manufactureCar() {
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fixChassis();
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fixBody();
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paint();
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fixInterior();
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}
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public String getChassis() {
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return chassis;
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}
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public void setChassis(String chassis) {
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this.chassis = chassis;
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}
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public String getBody() {
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return body;
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}
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public void setBody(String body) {
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this.body = body;
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}
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public String getPaint() {
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return paint;
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}
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public void setPaint(String paint) {
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this.paint = paint;
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}
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public String getInterior() {
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return interior;
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}
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public void setInterior(String interior) {
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this.interior = interior;
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}
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public String toString() {
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// StringBuilder class also uses Builder Design Pattern with implementation of
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// java.lang.Appendable interface
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StringBuilder builder = new StringBuilder();
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builder.append("Car [chassis=").append(chassis).append(", body=").append(body).append(", paint=").append(paint)
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.append(", interior=").append(interior).append("]");
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return builder.toString();
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}
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}
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Here please notice that manufactureCar() method is a template method here. And methods fixChassis(), fixBody(), paint() and fixInterior() are the steps which will be defined by different sub-classes. The template method uses and defines the sequence of steps to perform the algorithm.
Now we will implement concrete sub-classes to define different flavors of templates.
Here's the code for ClassicCar class:
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package org.trishinfotech.template;
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public class ClassicCar extends CarTemplate {
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public ClassicCar() {
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super();
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}
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public void fixChassis() {
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System.out.println("Assembling chassis of the classical model");
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this.chassis = "Classic Chassis";
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}
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public void fixBody() {
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System.out.println("Assembling body of the classical model");
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this.body = "Classic Body";
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}
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public void paint() {
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System.out.println("Painting body of the classical model");
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this.paint = "Classic White Paint";
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}
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public void fixInterior() {
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System.out.println("Setting up interior of the classical model");
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this.interior = "Classic interior";
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}
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}
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Here's the code for ModernCar class:
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package org.trishinfotech.template;
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public class ModernCar extends CarTemplate {
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public ModernCar() {
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super();
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}
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public void fixChassis() {
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System.out.println("Assembling chassis of the modern model");
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this.chassis = "Modern Chassis";
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}
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public void fixBody() {
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System.out.println("Assembling body of the modern model");
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this.body = "Modern Body";
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}
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public void paint() {
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System.out.println("Painting body of the modern model");
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this.paint = "Modern Black Paint";
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}
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public void fixInterior() {
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System.out.println("Setting up interior of the modern model");
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this.interior = "Modern interior";
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}
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}
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Here's the code for SportsCar class:
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package org.trishinfotech.template;
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public class SportsCar extends CarTemplate {
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public SportsCar() {
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super();
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}
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public void fixChassis() {
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System.out.println("Assembling chassis of the sports model");
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this.chassis = "Sporty Chassis";
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}
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public void fixBody() {
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System.out.println("Assembling body of the sports model");
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this.body = "Sporty Body";
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}
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public void paint() {
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System.out.println("Painting body of the sports model");
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this.paint = "Sporty Torch Red Paint";
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}
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public void fixInterior() {
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System.out.println("Setting up interior of the sports model");
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this.interior = "Sporty interior";
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}
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}
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Now we will write our Main class to execute and test the output:
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package org.trishinfotech.template;
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public class Main {
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public static void main(String[] args) {
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CarTemplate car = new SportsCar();
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car.manufactureCar();
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if (car != null) {
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System.out.println("Below car delievered: ");
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System.out.println("======================================================================");
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System.out.println(car);
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System.out.println("======================================================================");
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}
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}
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}
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Below is the output:
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Assembling chassis of the sports model
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Assembling body of the sports model
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Painting body of the sports model
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Setting up interior of the sports model
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Below car delievered:
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======================================================================
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Car [chassis=Sporty Chassis, body=Sporty Body, paint=Sporty Torch Red Paint, interior=Sporty interior]
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======================================================================
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Well, there you have it! I hope this tutorial helped to understand the Template Method pattern.
Source Code can be found here: Template-Method-Design-Pattern-Source-Code
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