Lab on Java generic types; exceptions

You may work in pairs on this lab.


Problem 1

Write a generic class Set with a type parameter T. The class uses an array of 100 elements of type T (initially just storing all NULL values). The class supports the following operations:
  1. void insert(T elt) - inserts an element into the set. An element is inserted into the first empty spot in the array. For now don't worry about the array being full - just do nothing if you can't insert an element. Also, don't worry about duplicate elements - just insert them.
  2. delete(T elt)
  3. - delete an element equal to elt (use the equals method to determine equality).
  4. T find(T elt) returns the first element equal to elt, as determined by equals method.
Test your code to create a Set of Strings (<String>Set) and a Set of Integers. Do not cast the elements returned by find - generic types don't require typecasting.
Can you insert a String into a Set of Integers? Explain what happens when you try.

Problem 2

Write an exception SetOverflow that gets thrown in insert method when the array is full. Write a try/catch block in your testing code to test the exception. The exception must extend Exception class, not RuntimeException.

Problem 3

Write an equals method for a Set class (two sets are equal if their arrays contain equals elements in the same order). Can you use instanceof T in your equals method? Why or why not? Use the equals methods of the elements to compare them.

Problem 4

Change the Set implementation so that it stores elements in the increasing order. In this implementation equal elements should be inserted only once. The implementation doesn't have to be efficient - you may shift all elements when inserting a new one. Note that in this case the class only works for Comparable elements, so in the class declaration you need to say <T extends Comparable>. Check that the only objects you can use it with are those implementing Comparable interface.
Submit all you code, write answers to questions in comments.


Eclipse supports for Java generics, so you can get meaningful error messages related to generics. Make sure that Eclipse is set to Java 1.5.
CSCi 4651 home page

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