Strategy Pattern

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A Strategy Pattern says that “defines a family of functionality, encapsulate each one, and make them interchangeable”.

The Strategy Pattern is also known as Policy.

Benefits:

  • It provides a substitute to subclassing.
  • It defines each behavior within its own class, eliminating the need for conditional statements.
  • It makes it easier to extend and incorporate new behavior without changing the application.

Usage:

  • When the multiple classes differ only in their behaviors.e.g. Servlet API.
  • It is used when you need different variations of an algorithm.

Strategy Pattern in (Core Java API’s) or JSE 7 API’s:

Strategy Pattern

Strategy Pattern in (Advance Java API’s) or JEE 7 API’s:

Strategy Pattern

UML for Strategy Pattern:

Strategy Pattern

Implementation of Strategy Pattern:

Step 1:

Create a Strategy interface.

public interface Strategy {

public float calculation(float a, float b);

}// End of the Strategy interface.

Step 2:

Create a Addition class that will implement Startegy interface.

//This is a class.  

public class Addition implements Strategy {

@Override

public float calculation(float a, float b) {

returna + b;

}

}// End of the Addition class.

Step 3:

Create a Subtraction class that will implement Startegy interface.

//This is a class.  

public class Subtraction implements Strategy {

@Override

public float calculation(float a, float b) {

returna – b;

}

}// End of the Subtraction class.

Step 4:

Create a Multiplication class that will implement Startegy interface.

public class Multiplication implements Strategy {

@Override

public float calculation(float a, float b) {

return a * b;

}

}// End of the Multiplication class.

Step 5:

Create a Context class that will ask from Startegy interface to execute the type of strategy.

public class Context {

private Strategy strategy;

public Context(Strategy strategy) {

this.strategy = strategy;

}

public float executeStrategy(float num1, float num2) {

return strategy.calculation(num1, num2);

}

}// End of the Context class.

Step 6:

Create a StartegyPatternDemo class.

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

public class StrategyPatternDemo {

public static void main(String[] args) throws NumberFormatException, IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

System.out.print(“Enter the first value: “);

float value1 = Float.parseFloat(br.readLine());

System.out.print(“Enter the second value: “);

float value2 = Float.parseFloat(br.readLine());

Context context = new Context(new Addition());

System.out.println(“Addition = “ + context.executeStrategy(value1, value2));

context = new Context(new Subtraction());

System.out.println(“Subtraction = “ + context.executeStrategy(value1, value2));

context = new Context(new Multiplication());

System.out.println(“Multiplication = “ + context.executeStrategy(value1, value2));

}

}// End of the StrategyPatternDemo class.

Output:

Strategy Pattern

 

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