Duplicate Code

Description (What)

Code that is duplicated in a class. Duplicated code may be harder to find if for example two methods do the exact same thing but have different names.

How to Locate It (Where)

Modern IDEs usually do a good job of finding duplicate code if configured correctly. Otherwise simply look for code snippets in your class that look eerily similar

How it Manifests (Why)

Two different developers might make two different functions that perform the same task unknowingly. This can also be caused by copy-pasting code snippets.

How to Fix It (Possible Treatments)

In Example 1, two methods perform identical functions but have different names in which case Extract Method is used to combine both the functions into a single function.

There are multiple possible situations in which duplicate code might arise, like when two subclasses have duplicate methods or if duplicate code is found in two different classes.

In Example 2, Extract Method is used, meaning that we could extract the reusable logics and make it a private method. This treatment is mainly used for some similar logic appearing

in the codebase for multiple times.

Other treatments are also possible based on the specific scenario, they can be found here

Examples

Example 1

Before:

Functions Add() and Sum() are functionally identical.

Observed Code Smells:
- Duplicate Code (lines 10-12, 26-29 )

After:

Applied Extract Method as it’s a duplication in the same class.

Refactoring Applied:
- Duplicate Code
    - Extract Method (Sum)

Observed Code Smells After Refactoring:
- None

Example 2

Before:

Usually, the duplicated part can be extracted as a method.

It may be just the code are produced by 2 different developers and someone has to refactor

to get rid of the duplication.

Observed Code Smells:
- Duplicated Code (lines 26-28, lines 41-43)

After:

Identify the duplicated code and extract them as a private helper method.

Refactoring Applied:
- Duplicated Code:
    - Extract method (lines 42-49)

Observed Code Smells After Refactoring:
- None

More about Duplicate Code

Example 1
Example 2

Before
After

001  class SimpleCalculator {
002      int a;
003      int b;
004  
005      public SimpleCalculator(int a, int b) {
006          this.a = a;
007          this.b = b;
008      }
009  
010      public int Add() {
011          return a + b;
012      }
013  
014      public int Subtract() {
015          return a - b;
016      }
017  
018      public int Multiply() {
019          return a * b;
020      }
021  
022      public int Divide() {
023          return a / b;
024      }
025  
026      public int Sum() {
027          int sum = a + b;
028          return sum;
029      }
030  }
031  
032  public class DUPCBE1 {
033      public static void main(String[] args) {
034          SimpleCalculator sc = new SimpleCalculator(10, 10);
035          sc.Add();
036          sc.Sum();
037      }
038  }
039