Strategy Design Pattern using Java Sample

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:

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

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

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 used by customers with the help of operator 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 in where the student is using a Calculator to fulfill his/her 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 the above code:

Summary

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