ArrayLists - Building Java Programs: A Back to Basics Approach - page 671

sorted. Many common types (such as String and
Integer ) implement Comparable .

You can implement the Comparable interface in your
own classes by writing a method compareTo .

Self-Check Problems

Section 10.1: ArrayList s
1. What is an ArrayList ? In what cases should you use an ArrayList rather than an array?
2. The next five questions refer to the following String elements:

["It", "was", "a", "stormy", "night"]
Write the code to declare an ArrayList containing these elements. What is the size of the list? What is its type?
3. Write code to insert two additional elements, "dark" and "and" , at the proper places in the list to produce the
following ArrayList as the result:

["It", "was", "a", "dark", "and", "stormy", "night"]
4. Write code to change the second element's value to "IS" , producing the following ArrayList as the result:

["It", "IS", "a", "dark", "and", "stormy", "night"]
5. Write code to remove from the list any String s that contain the letter "a" . The following should be the list's
contents after your code has executed:

["It", "IS", "stormy", "night"]
6. Write code to declare an ArrayList holding the first 10 multiples of 2: 0, 2, 4, . . . ,18. Use a loop to fill the list
with the proper elements.

7. Write a method named maxLength that takes an ArrayList of String s as a parameter and that returns the length
of the longest String in the list. If your method is passed an empty ArrayList , it should return 0 .
8. Write code to print out whether or not a list of String s contains the value "IS" . Do not use a loop.
9. Given the ArrayList from problem 3, write code to print out the index at which your list contains the value
“stormy” and the index at which it contains “dark”. Do not use a loop.

10. Given the ArrayList from problem 3, write a for-each loop that prints the uppercase version of each String in the
list on its own line.

11. When the code that follows runs on an ArrayList of String s, it throws an exception. Why?

for (String s : words) {
System.out.println(s);
if (s.equals("hello")) {
words.add("goodbye");

}

}
12. The code that follows does not compile. Why not? Explain how to fix it.

ArrayList<int> numbers = new ArrayList<int>();
numbers.add(7);