Dead Code

Description

Dead code is code that can never be executed in a running program. The surrounding code makes it impossible for a section of code to ever be executed.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The condition for the second if statement is impossible to satisfy. It requires that the variables be non-null. However, on the only path where s can be assigned a non-null value, there is a return statement.

String s = null;
if (b) {
  s = "Yes";
  return;
}

if (s != null) {
  Dead();
}

Example Two

In the following class, two private methods call each other, but since neither one is ever invoked from anywhere else, they are both dead code.

public class DoubleDead {
  private void doTweedledee() {
    doTweedledumb();
  }
  private void doTweedledumb() {
    doTweedledee();
  }
  public static void main(String[] args) {
    System.out.println("running DoubleDead");
  }
}

(In this case it is a good thing that the methods are dead: invoking either one would cause an infinite loop.)

Example Three

The field named glue is not used in the following class. The author of the class has accidentally put quotes around the field name, transforming it into a string constant.

public class Dead {

  String glue;

  public String getGlue() {
    return "glue";
  }

}

See Also