Lecture 18 Objectives

Lecture 24 Objectives [Dec 08]prev next

ART MOMENT: .

Almshouse Man in a Top Hat

Artist: Vincent van Gogh (1853-1890)

Date: 1882

With student id, museum tickets cost only $8

At the end of today's class you should

HAVE READ:

java.util.Iterator interface description (See Eclipse/Examples dec08 package).

KNOW:

what the methods of the java.util.Iterator interface
how to construct an Iterator from an existing Collection class, such as Hashtable or ArrayList
Know that Iterator expects underlying Collection to be unchanged while iteration occurs
Information from Handout.

BE ABLE TO:

Use Iterator to retrieve all elements from an ArrayList
Use Iterator to retrieve all key values for a Hashtable
Use Iterator to retrieve all value objects for a Hashtable

DAILY QUESTION:

What is wrong with the following code:

/**
* Take in an ArrayList of String objects, and output them all to
* the screen.
*/
public void outputAll (ArrayList al) {
    Iterator it2 = al.iterator();
    while (it2.next() != null) {
        String s = (String) it2.next();
        System.out.println (s);
    }
}

Sample Exam question(s)

1. You are given an ArrayList known to contain String values. Write a method using an Iterator that returns the number of Strings in the ArrayList that are four characters in length.

/**
* Take in an ArrayList of String objects and return the number of
* Strings that are four characters in length.
*/
public static int count(ArrayList al) {

// Fill in ....

}

2. Convert the following code from a while loop into a for loop

Iterator it = al.iterator();
while (it.hasNext()) {
String s = (String) it.next();
System.out.println (s);
}