Java Design Pattern: Template Method

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The Template Method design pattern defines the workflow for achieving a specific operation. It allows the subclasses to modify certain steps without changing the workflow’s structure.

The following example shows how Template Method pattern works.

Class diagram

template-method-pattern-class-diagram

Java Code

Vehicle.java defines a vehicle and hot it works

package com.programcreek.designpatterns.templatemethod;
 
abstract public class Vehicle {
	//set to protected so that subclass can access
	protected boolean status;
 
	abstract void start();
	abstract void run();
	abstract void stop();
 
	public void testYourVehicle(){
		start();
		if(this.status){
			run();
			stop();
		}	
	}
}

Car.java subclass Vehicle and defines concrete methods

package com.programcreek.designpatterns.templatemethod;
 
public class Car extends Vehicle {
 
	@Override
	void start() {
		this.status = true;
	}
 
	@Override
	void run() {
		System.out.println("Run fast!");
 
	}
 
	@Override
	void stop() {
		System.out.println("Car stop!");
	}
}

Truck.java subclass Vehicle and defines concrete methods

package com.programcreek.designpatterns.templatemethod;
 
public class Truck extends Vehicle {
 
	@Override
	void start() {
		this.status = true;
	}
 
	@Override
	void run() {
		System.out.println("Run slowly!");
	}
 
	@Override
	void stop() {
		System.out.println("Truck stop!");
 
	}
}

The testVehicle method only accept a Vehicle, it does not care if it is a car or truck, because they will work in the same way. This is an example of program to interface(P2I).

import com.programcreek.designpatterns.templatemethod.Car;
import com.programcreek.designpatterns.templatemethod.Truck;
import com.programcreek.designpatterns.templatemethod.Vehicle;
 
public class Main {
	public static void main(String args[]){
		Car car = new Car();
		testVehicle(car);
 
		Truck truck = new Truck();
		testVehicle(truck);
	}
 
	public static void testVehicle(Vehicle v){
		v.testYourVehicle();
	}
}

Real usage of Template Method Pattern

This pattern is used in Spring framework’s Data Access Object(DAO). org.springframework.jdbc.core.JdbcTemplate class has all the common repeated code blocks related with JDBC workflow, such as update, query, execute, etc.

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