Reading material

Section 8.1 (pages 334-338), Section 9.1 (pages 380-385)

Additional material

Implementation of a dictionary by means of a binary search tree in PostScript and PDF.

Dictionary

Question

Consider the following Java snippet.
  Dictionary d = new ...();
  d.insertItem(new Integer(2), new Object());
  if (d.findElement(new Integer(3)) == Dictionary.NO_SUCH_KEY))
  {
      System.out.println("Not found!");
  }
  else
  {
      System.out.println("Found!");
  }
Explain why we cannot use Dictionary.NO_SUCH_KEY.equals(d.findElement(new Integer(3))) instead of d.findElement(new Integer(3)) == Dictionary.NO_SUCH_KEY).