HW2 SAMPLE ANSWERS

1.
public String lookupEntry(String name) {
  int namePosition = find(name);
  if (namePosition != -1) {
      DirectoryEntry entry = directoryArray[namePosition];
      for (int index = namePosition-1; index >= 0; index--)
          directoryArray[index+1] = directoryArray[index];
          /* OR System.arraycopy(directoryArray, 0,
             directoryArray, 1, namePosition);
          */
      directoryArray[0] = entry;
      modified = true;
      return directoryArray[0].getNumber();
  }
  return null;        // if name not found
}

2.  Doubling the array size yields 10,20,40,80,160,320. Removing entries
does not resize, so the final size of the array is 320.

1/2 pt for correct answer
1/2 pt for explanation that's reasonable

3. If we just set the cell to null, when we traverse the array to look for
a name or number, we will get a NullPointerException when we hit the null
cell since no object reference is there.
Examples of this occur in any method that traverses the array and calls a
method on an object in each array cell (for example, find).

4. Changes:
  - add method to PhoneDirectory class for new operation
  - change processCommands in PDConsoleUI class to add extra menu option
  - add method to PDConsoleUI class to perform new operation
  - change processCommands in PDGUI class to add extra menu option
  - add method to PDGUI class to perform new operation

5. Any of these are ok:

A Java interface allow a programmer who uses a class that implements an
interface to write code without consulting with the programmer of the
class since it follows the definitions provided in the interface.

It allows us to remove one class that implements an interface and add in
another that implements the same interface without changing our other
application code (e.g. in the PhoneDirectory, we have two UIs, but the
code treats them as a PDUserInterface throughout).

A Java interface enforces that classes that implement the interface must
supply the specified methods in order to behave like other classes that
also implement the interface.

6. Checked - we must indicate for compiler what we will do if exception is
thrown (throws or try/catch) (e.g. IOException)
Unchecked - we don't have to write code to deal with these but if they
occur the program will still crash (e.g. ArrayIndexOutOfBoundsException,
NullPointerException, NumberFormatException, etc)

7. Test cases:
element in first position
element in last position
element somewhere in middle
element not in array
array has only one element
array has no elements
element occurs more than once

8.
/**
  Returns the index of the target an array if it occurs or -1 otherwise.
  @param data array containing the data to search through
  @param target value that we're looking for in array
  @return index of the target if found in the array or -1 if not found
 */