Java Reference
In-Depth Information
Self-Test Exercises
(continued)
4. Can you use the method
set
to place an element in an
ArrayList
at any index
you want?
5. Can you use the two-argument version of the method
add
to add an element in
an
ArrayList
at any index you want?
6. Consider the following two method invocations. Are there values of
index1
that
are allowed but that are not allowed for
index2
? Are there values of
index2
that
are allowed but that are not allowed for
index1
?
list
is an object of the class
ArrayList<String>
.
list.set(index1, "Hello");
list.add(index2, "Hello");
7. If you create an
ArrayList
with the following statement, can the
ArrayList
contain more than 20 elements?
ArrayList<Double> myList =
new
ArrayList<Double>(20);
Methods in the Class
ArrayList
With arrays, the square brackets and the instance variable
length
are the only tools
automatically provided for you, the programmer. If you want to use arrays for other
things, you must write code to manipulate the arrays.
ArrayList
s, on the other
hand, come with a selection of powerful methods that can do many of the things for
which you would need to write code in order to do with arrays. For example, the class
ArrayList
has a version of the method
add
that inserts a new element between two
elements in the
ArrayList
. Most of these methods are described in Display 14.1.
Display 14.1
Some Methods in the Class
ArrayList
(part 1 of 3)
CONSTRUCTORS
public
ArrayList<
Base_Type
>(
int
initialCapacity)
Creates an empty
ArrayList
with the specified
Base_Type
and initial capacity.
public
ArrayList<
Base_Type
>()
Creates an empty
ArrayList
with the specified
Base_Type
and an initial capacity of
10
.
ARRAYLIKE METHODS
public
Base_Type
set(
int
index,
Base_Type
newElement)
Sets the element at the specified
index
to
newElement
. Returns the element previously at that
position, but the method is often used as if it were
a void
method. If you draw an analogy between
the
ArrayList
and an array
a
, this statement is analogous to setting
a[index]
to the value
newElement
. The
index
must be a value greater than or equal to
0
and less than the current size of
the
ArrayList
. Throws an
IndexOutOfBoundsException
if the
index
is not in this range.
(continued)
