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Exercises

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  1. Create a new class called Gerbil with an int gerbilNumber that’s initialized in the constructor (similar to the Mouse example in this chapter). Give it a method called hop( ) that prints out which gerbil number this is and that it’s hopping. Create a Vector and add a bunch of Gerbil objects to the Vector. Now use the elementAt( ) method to move through the Vector and call hop( ) for each Gerbil.
  2. Modify Exercise 1 so you use an Enumeration to move through the Vector while calling hop( ).
  3. In AssocArray.java, change the example so it uses a Hashtable instead of an AssocArray.
  4. Take the Gerbil class in Exercise 1 and put it into a Hashtable instead, associating the name of the Gerbil as a String (the key) for each Gerbil (the value) you put in the table. Get an Enumeration for the keys( ) and use it to move through the Hashtable, looking up the Gerbil for each key and printing out the key and telling the gerbil to hop( ).
  5. Change Exercise 1 in Chapter 7 to use a Vector to hold the Rodents and an Enumeration to move through the sequence of Rodents. Remember that a Vector holds only Objects so you must use a cast (i.e.: RTTI) when accessing individual Rodents.
  6. (Intermediate) In Chapter 7, locate the GreenhouseControls.java example, which consists of three files. In Controller.java, the class EventSet is just a collection. Change the code to use a Stack instead of an EventSet. This will require more than just replacing EventSet with Stack; you’ll also need to use an Enumeration to cycle through the set of events. You’ll probably find it easier if at times you treat the collection as a Stack and at other times as a Vector.
  7. (Challenging). Find the source code for Vector in the Java source code library that comes with all Java distributions. Copy this code and make a special version called intVector that holds only ints. Consider what it would take to make a special version of Vector for all the primitive types. Now consider what happens if you want to make a linked list class that works with all the primitive types. If parameterized types are ever implemented in Java, they will provide a way to do this work for you automatically (as well as many other benefits).
  8. e


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