Understanding Open/Closed Principle (OCP) from the SOLID OO principles with a Java example

Posted on November 22, 2014 by

Q. Is there anything wrong with the following class design? If yes, can the design be improved?

 package com.ocp;
import javax.management.RuntimeErrorException;
import org.apache.commons.lang.StringUtils;
public class MathOperation {
 
 public int operate(int input1, int input2, String operator){
  
  if(StringUtils.isEmpty(operator)){
   throw new IllegalArgumentException("Invalid operator: " + operator);
  }
  
  if(operator.equalsIgnoreCase("+")){
   return input1 + input2;
  }
  else if(operator.equalsIgnoreCase("*")){
   return input1 * input2; 
  } else {
   throw new RuntimeException("unsupported operator: " + operator);
  }
 }
}

package com.ocp;

import javax.management.RuntimeErrorException;

import org.apache.commons.lang.StringUtils;

public class MathOperation {

public int operate(int input1, int input2, String operator){

if(StringUtils.isEmpty(operator)){

throw new IllegalArgumentException("Invalid operator: " + operator);

}

if(operator.equalsIgnoreCase("+")){

return input1 + input2;

}

else if(operator.equalsIgnoreCase("*")){

return input1 * input2;

} else {

throw new RuntimeException("unsupported operator: " + operator);

}

JUnit test class.

 package com.ocp;
import junit.framework.Assert;
import org.junit.Before;
import org.junit.Test;
public class MathOperationTest {
 
 MathOperation operation;
 
 @Before
 public void init(){
  operation = new MathOperation();
 }
 
 @Test
 public void testAddition() {
  Assert.assertEquals(8, operation.operate(5, 3, "+"));
 }
 
 @Test
 public void testMultiplication() {
  Assert.assertEquals(15, operation.operate(5, 3, "*"));
 }
}

package com.ocp;

import junit.framework.Assert;

import org.junit.Before;

import org.junit.Test;

public class MathOperationTest {

MathOperation operation;

@Before

public void init(){

operation = new MathOperation();

}

@Test

public void testAddition() {

Assert.assertEquals(8, operation.operate(5, 3, "+"));

}

@Test

public void testMultiplication() {

Assert.assertEquals(15, operation.operate(5, 3, "*"));

}

A. It’s not a good idea to try to anticipate changes in requirements ahead of time, but you…

Understanding Open/Closed Principle (OCP) from the SOLID OO principles with a Java example

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