Strategy Design Pattern using a Java Sample

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

package com.sdp;
public interface IOperator {
void executeOperation(int a, int b);
}

Below are the concrete operators which implement a contract defined by IOperator:

package com.sdp;
public class AddOperator implements IOperator {
@Override
public void executeOperation(int a, int b) {
System.out.println("AddOperator result: " + (a + b));
}
}

package com.sdp;
public class SubtractOperator implements IOperator {
@Override
public void executeOperation(int a, int b) {
System.out.println("SubtractOperator result: " + (a - b));
}
}

package com.sdp;
public class MultiplyOperator implements IOperator {
@Override
public void executeOperation(int a, int b) {
System.out.println("MultiplyOperator result: " + (a * b));
}
}

package com.sdp;
public class DivisionOperator implements IOperator {
@Override
public void executeOperation(int a, int b) {
System.out.println("DivisionOperator result: " + (a / b));
}
}

Below is the our product calculator which is going to be used by customers with the help of the IOperator contract:

package com.sdp;
public class Calculator {
private IOperator _operator;
public Calculator(IOperator ioperator)
{
_operator = ioperator;
}
public void Calculate(int a, int b)
{
_operator.executeOperation(a, b);
}
}

Below is the Student class where the student is using the Calculator to fulfill their requirement:

package com.sdp;
public class Student {
public static void main(String[] args) {
Calculator oprt = new Calculator(new AddOperator());
oprt.Calculate(20, 10);
oprt = new Calculator(new SubtractOperator());
oprt.Calculate(20, 10);
oprt = new Calculator(new MultiplyOperator());
oprt.Calculate(20, 10);
oprt = new Calculator(new DivisionOperator());
oprt.Calculate(20, 10);
}
}

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.