Introduction

A strategic design pattern is a behavioural design pattern in which the behaviour of the object is encapsulated with a common function name.

Where to use Strategic design pattern?

When different customer have a common strategy, (common operation name), but a different action to perform; then we can use a strategic design pattern.

Why to use Strategic design pattern?

As we discussed previously customers have common operation name to perform, so that we can share a common interface to all customers to perform their actions as per there need.
Players in this pattern
  • Strategy: It defines contract with common operation.
  • ConcreteStrategy : It implements contact defined by Strategy.
  • Product: It fulfil customer requirements using ConcreteStrategy objects by referring Strategy contract.
We will see strategic design pattern with an example:

Problem definition

Define a common operation for a student to access different actions, such as addition, subtraction, multiplication, and division.
Players in this case:
  • Strategy : IOperator
  • ConcreteStrategy: AddOperator, SubtractOperator, MultiplyOperator, DivisionOperator.
  • Product : Calculator
Below is the IOperator contract which defined a common operation called ExecuteOperation
  1. package com.sdp;
  3. public interface IOperator {
  4. void executeOperation(int a, int b);
  5. }
Below are the concrete operators which implement a contract defined by IOperator:
  1. package com.sdp;
  3. public class AddOperator implements IOperator {
  4. @Override
  5. public void executeOperation(int a, int b) {
  6. System.out.println("AddOperator result: " + (a + b));
  7. }
  8. }
  1. package com.sdp;
  3. public class SubtractOperator implements IOperator {
  4. @Override
  5. public void executeOperation(int a, int b) {
  6. System.out.println("SubtractOperator result: " + (a - b));
  7. }
  8. }
  1. package com.sdp;
  3. public class MultiplyOperator implements IOperator {
  4. @Override
  5. public void executeOperation(int a, int b) {
  6. System.out.println("MultiplyOperator result: " + (a * b));
  7. }
  8. }
  1. package com.sdp;
  3. public class DivisionOperator implements IOperator {
  4. @Override
  5. public void executeOperation(int a, int b) {
  6. System.out.println("DivisionOperator result: " + (a / b));
  7. }
  8. }
Below is the our product calculator which is going to be used by customers with the help of the IOperator contract:
  1. package com.sdp;
  3. public class Calculator {
  5. private IOperator _operator;
  7. public Calculator(IOperator ioperator)
  8. {
  9. _operator = ioperator;
  10. }
  12. public void Calculate(int a, int b)
  13. {
  14. _operator.executeOperation(a, b);
  15. }
  16. }
Below is the Student class where the student is using the Calculator to fulfill their requirement:
  1. package com.sdp;
  3. public class Student {
  5. public static void main(String[] args) {
  6. Calculator oprt = new Calculator(new AddOperator());
  7. oprt.Calculate(20, 10);
  9. oprt = new Calculator(new SubtractOperator());
  10. oprt.Calculate(20, 10);
  12. oprt = new Calculator(new MultiplyOperator());
  13. oprt.Calculate(20, 10);
  15. oprt = new Calculator(new DivisionOperator());
  16. oprt.Calculate(20, 10);
  17. }
  18. }
Below is the snap of output window of above code:

Summary

In this article, we learned what a strategic design pattern is and how to use it.