Strategy Pattern

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 in (Advance Java API's) or JEE 7 API's:

UML for Strategy Pattern:

Implementation of Strategy Pattern:

Step 1:

Create a Strategy interface.

//This is an 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) {
		return a+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) {
		return a-b;
	}

}// End of the Subtraction class.

Step 4:

Create a Multiplication class that will implement Startegy interface.

//This is a class.

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.

//This is a class.


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.

//This is a 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: