LISTS, STACKS, QUEUES, AND PRIORITY QUEUES - Introduction to Java Programming: Comprehensive Version - page 767

NEW YORK ATLANTA DALLAS MADISON

The program creates a concrete collection object using ArrayList (line 5) and adds four
strings into the list (lines 6-9). The program then obtains an iterator for the collection (line 11)
and uses the iterator to traverse all the strings in the list and displays the strings in uppercase
(lines 12-14).

Tip
You can simplify the code in lines 11-14 using a foreach loop without using an iterator,
as follows:

foreach loop

for (String element: collection)
System.out.print(element.toUpperCase() + " " );

This loop is read as “for each element in the collection, do the following.” The foreach
loop can be used for arrays (see Section 7.2.7) as well as any instance of Iterable .

20.6

✓ ✓

How do you obtain an iterator from a collection object?

Check

20.7

What method do you use to obtain an element in the collection from an iterator?

Point

20.8

Can you use a foreach loop to traverse the elements in any instance of Collection ?

20.9

When using a foreach loop to traverse all elements in a collection, do you need to use
the next() or hasNext() methods in an iterator?

20.4 Lists
The List interface extends the Collection interface and defines a collection for
storing elements in a sequential order. To create a list, use one of its two concrete
classes: ArrayList or LinkedList .

Key
Point

We used ArrayList to test the methods in the Collection interface in the preceding
sections. Now we will examine ArrayList in more depth. We will also introduce another
useful list, LinkedList , in this section.

20.4.1 The Common Methods in the List Interface
ArrayList and LinkedList are defined under the List interface. The List interface
extends Collection to define an ordered collection with duplicates allowed. The List
interface adds position-oriented operations, as well as a new list iterator that enables the user
to traverse the list bidirectionally. The methods introduced in the List interface are shown
in Figure 20.3.
The add(index, element) method is used to insert an element at a specified index, and
the addAll(index, collection) method to insert a collection of elements at a specified
index. The remove(index) method is used to remove an element at the specified index from
the list. A new element can be set at the specified index using the set(index, element)
method.
The indexOf(element) method is used to obtain the index of the specified element's
first occurrence in the list, and the lastIndexOf(element) method to obtain the index of
its last occurrence. A sublist can be obtained by using the subList(fromIndex, toIndex)
method.