Java Design Patterns Tutorial - Java Design Pattern - Strategy Pattern

In Strategy pattern, an algorithm can be changed at run time.

Strategy pattern is a behavior pattern.

In Strategy pattern, we create objects to represent various algorithms and a context object to run the algorithm.

The strategy object changes the algorithm on the context object.

Example

interface MathAlgorithm {
   public int calculate(int num1, int num2);
}//from  w  w  w .  java 2  s. c om
class MathAdd implements MathAlgorithm{
   @Override
   public int calculate(int num1, int num2) {
      return num1 + num2;
   }
}
class MathSubstract implements MathAlgorithm{
   @Override
   public int calculate(int num1, int num2) {
      return num1 - num2;
   }
}
class MathMultiply implements MathAlgorithm{
   @Override
   public int calculate(int num1, int num2) {
      return num1 * num2;
   }
}
class MathContext {
   private MathAlgorithm algorithm;

   public MathContext(MathAlgorithm strategy){
      this.algorithm = strategy;
   }

   public int execute(int num1, int num2){
      return algorithm.calculate(num1, num2);
   }
}
public class Main {
   public static void main(String[] args) {
      MathContext context = new MathContext(new MathAdd());    
      System.out.println("10 + 5 = " + context.execute(10, 5));

      context = new MathContext(new MathSubstract());    
      System.out.println("10 - 5 = " + context.execute(10, 5));

      context = new MathContext(new MathMultiply());    
      System.out.println("10 * 5 = " + context.execute(10, 5));
   }
}

The code above generates the following result.