Introduction

Strategy design pattern is a behavioral design pattern in which the behavior of the object is encapsulated with a common function name.

Where to use a Strategic design pattern?

We can use strategic design pattern when a different customer has a common strategy (Common operation name) but a different action to perform.

Why use a Strategic design pattern?

As discussed previously, customers have a common operation name to perform. With a strategic design pattern, we can share a common interface to all customers to perform their actions as per their need.
Players in this pattern
  • Strategy: Defines a contract with a common operation.
  • ConcreteStrategy: Implements contact defined by the Strategy.
  • Product: Fulfills customer requirements using ConcreteStrategy objects by referring Strategy contract.
Now we will see a strategic design pattern with an example:
Problem definition: Define a common operation to student to access different actions like Addition, subtraction, multiplication, division.
Players in this case:
  • Strategy: operator
  • ConcreteStrategy: AddOperator, SubtractOperator, MultiplyOperator, DivisionOperator.
  • Product: Calculator
Below is the operator contract which defines 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 as defined by the operator:
  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. }
  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 used by customers with the help of operator 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 in where the student is using a Calculator to fulfill his/her 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 the above code:

Summary

In this blog, we understood about what strategy and design pattern are and how to use them.