Strategy Design pattern - Implementation [Travel]

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Real-World Scenario: Choosing a Travel Mode

When planning a trip, a traveler can reach their destination using different modes of transportation: Car, Bus, Train, or Flight. Each option has its own cost, travel duration, and route logic.

In software design, modeling this with hardcoded conditions creates rigid, messy code. By applying the Strategy Design Pattern, each travel option becomes an interchangeable strategy class that can be switched dynamically at runtime.

Why Use the Strategy Pattern Here?

• Extensibility: Need to add bike or ferry travel later? Add a new class without modifying existing travel logic.
• Clean Code: Eliminates complicated switch-case or conditional branches inside your booking engine.
• Runtime Selection: Users can change their travel preference dynamically based on budget or schedule.

Components of the Architecture

• TravelStrategy (Interface): Declares common methods like travel(String source, String destination).
• Concrete Strategies: Classes such as CarTravelStrategy, BusTravelStrategy, or FlightTravelStrategy.
• Traveler / Context: Holds a reference to the selected TravelStrategy and executes the journey.

Java Code Walkthrough

1. Define the Common Strategy Interface:

public interface TravelStrategy {
    void gotoAirport(String source, String destination);
}

2. Implement Concrete Strategies:

public class TaxiTravelStrategy implements TravelStrategy {
    @Override
    public void gotoAirport(String source, String destination) {
        System.out.println("Traveling from " + source + " to " + destination + " by Taxi.");
    }
}

3. Build the Travel Context:

public class TravelContext {
    private TravelStrategy travelStrategy;

    public void setTravelStrategy(TravelStrategy travelStrategy) {
        this.travelStrategy = travelStrategy;
    }

    public void travel(String source, String destination) {
        travelStrategy.gotoAirport(source, destination);
    }
}

Related Design Pattern Tutorials to Watch Next

• Strategy Design pattern: Key Points
• Strategy Design Pattern Implementation: Compressing Files
• Strategy Design Pattern: Class Diagram Explained

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Strategy Design pattern - Implementation [Travel]

Strategy Design pattern - Implementation [Travel] - Class Diagram

TravelStrategy.java

public interface TravelStrategy
{
public void gotoAirport();
}

AutoTravelStrategy.java

public class AutoTravelStrategy implements TravelStrategy
{

public void gotoAirport()
{
System.out.println("Traveler is going to Airport by Auto and will be charged 600 Rs");
}

}

BusTravelStrategy.java

public class BusTravelStrategy implements TravelStrategy
{

public void gotoAirport()
{
System.out.println("Traveler is going to Airport by bus and will be charged 200 Rs");
}

}

TaxiTravelStrategy.java

public class TaxiTravelStrategy implements TravelStrategy
{

public void gotoAirport()
{
System.out.println("Traveler is going to Airport by Taxi and will be charged 1000 Rs");
}

}


TrainTravelStrategy.java

public class TrainTravelStrategy implements TravelStrategy
{

public void gotoAirport()
{
System.out.println("Traveler is going to Airport by Train and will be charged 300 Rs");
}

}


TravelContext.java

public class TravelContext
{
private TravelStrategy travelStrategy;

// Client will set what TravelStrategy to use by calling this method
public void setTravelStrategy(TravelStrategy strategy)
{
this.travelStrategy = strategy;
}

public TravelStrategy getTravelStrategy()
{
return travelStrategy;
}

public void gotoAirport()
{
travelStrategy.gotoAirport();
}

}


Traveler.java

import java.util.Scanner;

public class Traveler
{

public static void main( String[] args )
{

System.out.println("Please enter Travel Type : 'Bus' or 'Train' or 'Taxi' or 'Auto' ");
Scanner scanner = new Scanner(System.in);
String travelType = scanner.next();
System.out.println("Travel type is : " + travelType);

TravelContext ctx = null;
ctx = new TravelContext();

if( "Bus".equalsIgnoreCase(travelType) )
{
ctx.setTravelStrategy(new BusTravelStrategy());
}
else if("Train".equalsIgnoreCase(travelType))
{
ctx.setTravelStrategy(new TrainTravelStrategy());
}
else if("Taxi".equalsIgnoreCase(travelType))
{
ctx.setTravelStrategy(new TaxiTravelStrategy());
}
else if("Auto".equalsIgnoreCase(travelType))
{
ctx.setTravelStrategy(new AutoTravelStrategy());
}
System.out.println("Travel context has : "+ctx.getTravelStrategy());
ctx.gotoAirport();

}
}


Output

Please enter Travel Type : 'Bus' or 'Train' or 'Taxi' or 'Auto'
bus
Travel type is : bus
Travel context has : BusTravelStrategy@1e4cbc4
Traveler is going to Airport by bus and will be charged 200 Rs

Please enter Travel Type : 'Bus' or 'Train' or 'Taxi' or 'Auto' 

train

Travel type is : train

Travel context has : TrainTravelStrategy@578ceb

Traveler is going to Airport by Train and will be charged 300 Rs