CodeQL documentation

Constant loop condition

ID: java/constant-loop-condition
Kind: problem
Severity: warning
Precision: very-high
Tags:
   - correctness
   - external/cwe/cwe-835
Query suites:
   - java-security-and-quality.qls

Click to see the query in the CodeQL repository

Loops can contain multiple exit conditions, either directly in the loop condition or as guards around break or return statements. If none of the exit conditions can ever be satisfied, then the loop will never terminate.

Recommendation

When writing a loop that is intended to terminate, make sure that all the necessary exit conditions can be satisfied and that loop termination is clear.

Example

The following example searches for a field of a given name, and intends to throw an exception if the field cannot be found. However, if the field cannot be found, the double loop structure means that the exit conditions will never be met, resulting in an infinite loop.

Object getField(Object obj, String name) throws NoSuchFieldError {
  Class clazz = obj.getClass();
  while (clazz != null) {
    for (Field f : clazz.getDeclaredFields()) {
      if (f.getName().equals(name)) {
        f.setAccessible(true);
        return f.get(obj);
      }
    }
  }
  throw new NoSuchFieldError(name);
}

The solution is to rewrite the code as follows using an if-statement.

Object getField(Object obj, String name) throws NoSuchFieldError {
  Class clazz = obj.getClass();
  if (clazz != null) {
    for (Field f : clazz.getDeclaredFields()) {
      if (f.getName().equals(name)) {
        f.setAccessible(true);
        return f.get(obj);
      }
    }
  }
  throw new NoSuchFieldError(name);
}

References