LISTS, STACKS, QUEUES, AND PRIORITY QUEUES - Introduction to Java Programming: Comprehensive Version - page 771

A list of integers in the array list:
[10, 1, 2, 30, 3, 1, 4]
Display the linked list forward:
green 10 red 1 2 30 3 1
Display the linked list backward:
1 3 30 2 1 red 10 green

A list can hold identical elements. Integer 1 is stored twice in the list (lines 6, 9). ArrayList
and LinkedList operate similarly. The critical difference between them pertains to internal
implementation, which affects their performance. ArrayList is efficient for retrieving ele-
ments and LinkedList is efficient for inserting and removing elements at the beginning of
the list. Both have the same performance for inserting and removing elements in the middle
or at the end of the list.
The get(i) method is available for a linked list, but it is a time-consuming operation. Do
not use it to traverse all the elements in a list as shown in (a). Instead you should use an iterator
as shown in (b). Note that a foreach loop uses an iterator implicitly. You will know the reason
when you learn how to implement a linked list in Chapter 24.

for ( int i = 0 ; i < list.size(); i++) {
process list.get(i);
}

for (listElementType s: list) {
process s;
}

(a) Very inefficient (b) Efficient

Tip
Java provides the static asList method for creating a list from a variable-length list of
arguments. Thus you can use the following code to create a list of strings and a list of
integers:

Arrays.asList(T... a)
method

List<String> list1 = Arrays.asList( "red" , "green" , "blue" );
List<Integer> list2 = Arrays.asList( 10 , 20 , 30 , 40 , 50 );

20.10

✓ ✓

How do you add and remove elements from a list? How do you traverse a list in both
directions?

Check

Point

20.11

Suppose that list1 is a list that contains the strings red , yellow , and green , and
that list2 is another list that contains the strings red , yellow , and blue . Answer
the following questions:
a. What are list1 and list2 after executing list1.addAll(list2) ?
b. What are list1 and list2 after executing list1.add(list2) ?
c. What are list1 and list2 after executing list1.removeAll(list2) ?
d. What are list1 and list2 after executing list1.remove(list2) ?
e. What are list1 and list2 after executing list1.retainAll(list2) ?
f. What is list1 after executing list1.clear() ?

20.12

What are the differences between ArrayList and LinkedList ? Which list should
you use to insert and delete elements at the beginning of a list?

20.13

Are all the methods in ArrayList also in LinkedList ? What methods are in
LinkedList but not in ArrayList ?

20.14

How do you create a list from an array of objects?