Espresso: A Concentrated Introduction to Java

Laboratory: Vectors in Java

Summary: In this laboratory, you will explore some subtleties of the utility class java.util.Vector.

References:

• API for java.util.Vector.

Contents:

• Exercises
  • Exercise 0: Preparation
  • Exercise 1: Starting Your Tester
  • Exercise 2: Adding Elements
  • Exercise 3: Removing Values
  • Exercise 4: Setting Values
  • Exercise 5: Setting Values, Revisited
  • Exercise 6: Comparing Methods

Exercises

Exercise 0: Preparation

a. Create a package named username.vectors in project Code.

b. Open a separate window with the reference for java.util.Vector.

Exercise 1: Starting Your Tester

Write a main class, username.vectors.TestVector that (a) builds an empty vector of Strings (using the zero-parameter constructor) and (b) prints all the elements in the vector using code that will continue to work if we add elements. Hint: You'll need a for loop.

Exercise 2: Adding Elements

As you may have noted, vectors provide two kinds of add methods: One that adds to the end, and one that adds in a specified location.

a. Verify that adding to the index 0 an empty vector succeeds. (Use the two-parameter add.)

b. Verify that adding to the end of that one-element vector succeeds. (Use the one-parameter add.)

c. What do you think will happen if you add an element at index 0 in this two-element vector?

d. Verify your answer to step c experimentally.

e. What do you think will happen if you add an element at index 10 in this new vector?

f. Verify your answer to step e experimentally.

Exercise 3: Removing Values

As you may have noted, vectors provide two kinds of remove methods: One that removes by index and one that removes by value. We will focus on the first.

a. What do you expect to happen if you remove the element at index 0 in a non-empty vector?

b. Verify your answer experimentally.

c. What do you expect to happen if you attempt to remove an element at an index greater than the size of the vector?

d. Verify your answer experimentally.

Exercise 4: Setting Values

As you may have noted, vectors also provide two mechanisms for setting values in an array, set and setElementAt.

a. What, in your reading of the documentation is the difference between set and setElementAt?

For the remaining parts of this exercise, use set.

b. What do you expect to happen if you set the value at position 0 in an empty vector?

c. Verify your answer experimentally.

d. What do you expect to happen if you set the value at position 0 in a two-element vector?

e. Verify your answer experimentally.

f. What do you expect to happen if you set the value at position 2 in a two-element vector?

g. Verify your answer experimentally.

h. What do you expect to happen if you set the value at position 3 in a two-element vector?

i. Verify your answer experimentally.

Exercise 5: Setting Values, Revisited

Redo the previous exercise, using setElementAt rather than set.

Exercise 6: Comparing Methods

Explain the difference between add (the two-parameter version), set, and setElementAt.

History

Tuesday, 19 April 2005 [Samuel A. Rebelsky]

• Wrote lab.
• Released.

Tuesday, 25 October 2005 [Samuel A. Rebelsky]

• Some minor corrections.
• Removed one problem.

Tuesday, 7 March 2006 [Samuel A. Rebelsky]

• Minor edits.