Dead Code

Description (What)

Dead code is any piece of code (method, line, field) that is unused or unreachable.

How to Locate It (Where)

Most modern IDEs and Linters have inbuilt dead code detection for public methods and fields and gray out or highlight dead code.

In cases where a field or method is private, your IDE might not gray about dead code, in which case it is imperative to go through your class to make sure any private method or field is not going unused.

How It Manifests (Why)

Sometimes better, newer or simply different methods are created to superseed older methods. In these cases, the older method become dead code since they are not used anymore. Sometimes methods and fields or variables are created in anticipation of being used in the future but simply remain unused.

How to Fix It (Possible Treatments)

Simply delete the unused (dead) methods or fields or variables.

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

Examples

Example 1

Before:

Shipment class has dead method calculateDistance which has been

superseeded by method calculateDistanceFast and thus also making

method degToRad dead.

Observed Code Smells:
- Dead Code (lines 9-14, 27-29)

After:

Deleted unused dead methods calculateDistance and degToRad.

Refactoring Applied:
- Dead Code
    - Deleted unused methods (calculateDistance and degToRad)

Observed Code Smells After Refactoring:
- None

Example 2

Before:

The method calculate2018BlackFridayPrice is no longer applicable.

Need to be refactored or deleted.

Observed Code Smells:
-  Dead Code (line 34-50)

After:

Simple delete the code.

Refactoring Applied:
- Dead Code:
    - Remove Method (No longer exist).

Observed Code Smells After Refactoring:
- None

When to Ignore

None

More about Dead Code

Example 1
Example 2

Before
After

001  class Shipment {
002      private final double VEHICLESPEEDKMPH;
003      private final int EARTHRADIUS;
004      LocationCoordinates originCity;
005      LocationCoordinates destCity;
006  
007      public double calculateDistanceFast() {
008          double p = Math.PI / 180;
009          double a = 0.5 - Math.cos((destCity.getLatitude() - originCity.getLatitude()) * p) / 2
010                  + Math.cos(originCity.getLatitude() * p) * Math.cos(destCity.getLatitude() * p)
011                          * (1 - Math.cos((destCity.getLongitude() - originCity.getLongitude()) * p)) / 2;
012          return 2 * this.EARTHRADIUS * Math.asin(Math.sqrt(a));
013      }
014  
015      public double calculateDistance() {
016          double dLat = degToRad(destCity.getLatitude() - originCity.getLatitude());
017          double dLon = degToRad(destCity.getLongitude() - originCity.getLongitude());
018          double a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
019                  Math.cos(degToRad(originCity.getLatitude())) * Math.cos(degToRad(destCity.getLatitude())) *
020                          Math.sin(dLon / 2) * Math.sin(dLon / 2);
021          double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
022          double d = this.EARTHRADIUS * c;
023          return d;
024      }
025  
026      private double degToRad(double deg) {
027          return deg * (Math.PI / 180);
028      }
029  
030      public double calculateTimeInHours() {
031          return calculateDistanceFast() / this.VEHICLESPEEDKMPH;
032      }
033  
034      public Shipment(LocationCoordinates city1, LocationCoordinates city2) {
035          this.EARTHRADIUS = 6371;
036          this.VEHICLESPEEDKMPH = 55.4;
037          this.originCity = city1;
038          this.destCity = city2;
039      }
040  }
041  
042  class LocationCoordinates {
043      private double longitude;
044      private double latitude;
045  
046      public double getLatitude() {
047          return latitude;
048      }
049  
050      public double getLongitude() {
051          return longitude;
052      }
053  
054      public LocationCoordinates(double longitude, double latitude) {
055          this.longitude = longitude;
056          this.latitude = latitude;
057      }
058  
059      public double getRelativePositionToPoles(String direction) {
060          if(direction.equals("North")) {
061              return 90 - latitude;
062          } else if(direction.equals("South")) {
063              return 90 + latitude;
064          } else {
065              return 181;
066          }
067      }
068  
069  }
070  
071  public class DEDCBE1 {
072      public static void main(String[] args) {
073          LocationCoordinates boston = new LocationCoordinates(42.3555, 71.0565);
074          LocationCoordinates newYork = new LocationCoordinates(40.7128, 74.0060);
075          Shipment cst = new Shipment(boston, newYork);
076          System.out.println(cst.calculateTimeInHours());
077          System.out.println(boston.getRelativePositionToPoles("North"));
078      }
079  
080  }
081