ThisCanBeNull

DRAFT

Correction

Here is what's right.

The this variable (a special local variable) never is null. The variable exists during activations of instance methods, and it always points to the instance on which the method operates. That instance always exists, thus the this variable never is null.

Example

The following code was produced by a student as part of a linked list implementation (after seeing a different implementation using a sentinel/null object, and having to produce an implementation that does not use a null object to terminate the list):

public class IntList {

  private int value;
  private IntList tail;

  public int length() {
    if (this==null) {
      return 0;
    } else if (this.tail == null) {
      return 1;
    } else {
      this.tail.length();
    }
  }
}