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.