Template Method Pattern

The Template Method Pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.

Template Method Pattern Diagram

Implementation

Creating an Abstract Class:

public abstract class CaffeineBeverage {
 
	/* Template Method */
	final void prepareRecipe() {
		boilWater();
		brew();
		pourInCup();
		if (customerWantsCondiments()) {
			addCondiments();
		}
	}
	
	/* Primitive Methods */
	abstract void brew();
	abstract void addCondiments();
	
	void boilWater() {
		System.out.println("Boiling water");
	}
	
	void pourInCup() {
		System.out.println("Pouring into cup");
	}
	
	/* Hook
	Subclass can choose either to implmenent it or not */
	boolean customerWantsCondiments() {
		return true;
	}
 
}

Creating a Concrete Class:

public class Coffee extends CaffeineBeverage {
 
	public void brew() {
		System.out.println("Dripping Coffee through filter");
	}
	
	public void addCondiments() {
		System.out.println("Adding Sugar and Milk");
	}
 
	/* Overrding Hook */
	public boolean customerWantsCondiments() {
		String answer = getUserInput();
		if (answer.toLowerCase().startsWith("y")) {
			return true;
		} else {
			return false;
		}
	}
 
	private String getUserInput() {
		String answer = null;
		System.out.print("Would you like milk and sugar with your coffee (y/n)? ");
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
	
		try {
			answer = in.readLine();
		} catch (IOException ioe) {
			System.err.println("IO error trying to read your answer");
		}
		
		if (answer == null) {
			return "no";
		}
		return answer;
	}
 
}

Testing:

public class BeverageTestDrive {
 
	public static void main(String[] args) {
 
		Tea teaHook = new Tea();		
		Coffee coffeeHook = new Coffee();
		
		System.out.println("\nMaking tea...");
		teaHook.prepareRecipe();
		System.out.println("\nMaking coffee...");
		coffeeHook.prepareRecipe();
	}
}

Real Example

Creating a Concrete class that implements Comparable template:

public class Duck implements Comparable<Duck> {
	String name;
	int weight;
	
	public Duck(String name, int weight) {
		this.name = name;
		this.weight = weight;
	}
 
	public String toString() {
		return name + " weighs " + weight;
	}
 
	/* Hook */
	public int compareTo(Duck otherDuck) {
		if (this.weight < otherDuck.weight) {
			return -1;
		} else if (this.weight == otherDuck.weight) {
			return 0;
		} else { // this.weight > otherDuck.weight
			return 1;
		}
	}
}

Testing:

 
public class DuckSortTestDrive {
 
	public static void main(String[] args) {
		Duck[] ducks = {
			new Duck("Daffy", 8),
			new Duck("Dewey", 2),
			new Duck("Howard", 7),
			new Duck("Louie", 2),
			new Duck("Donald", 10),
			new Duck("Huey", 2)
		};
	
		System.out.println("Before sorting:");
		display(ducks);
		Arrays.sort(ducks);
		System.out.println("\nAfter sorting:");
		display(ducks);
	}
	
	public static void display(Duck[] ducks) {
		for (Duck d : ducks) {
			System.out.println(d);
		}
	}
}