Java Reference
In-Depth Information
Class ArrayList
. Class
Vector
has been in the API package
java.util
from the beginning. In
the latest version of Java, a new class
ArrayList
was added to package
java.util
. It has roughly the same functionality as
Vector
: an object contains
size
() elements and has a capacity; elements can be added, deleted, accesssed,
changed, searched for, and so on. Use either
ArrayList
or
Vector
—it is your
or your instructor's choice.
We introduce non-Java notation to help us talk about the elements of a
Vector v
:
•
v[2]
refers to the element numbered
2
.
•
v[h]
refers to the element given by the value of expression
h
.
•
v[h..k]
refers to the list of elements numbered
h,h+1
, …,
k
.
•
v[h..]
refers to the elements numbered
h
,
h+1
, …,
v.size() - 1
For example, if
v
is (or contains the name of) the object in Fig. 5.3, then
v[2]
is the string
"blue"
,
v[0..1]
consists of
4
,
"red"
, and
v[0..]
is the whole
list of values.
In the notation
v[i]
,
i
is called the index of the element.
5.3.1
Creating and adding to a Vector
The declaration
Activity
5-5.1
Vector d=
new
Vector(5);
creates an instance of class
Vector
that can hold
5
objects and stores the name
of the instance in variable
d
. Instance
d
can hold
5
objects, but at the moment it
does not hold any; its capacity is
5
, but its size is
0
. (There is also a constructor
with no parameters, which creates a
Vector
with capacity
10
.)
Instance function
add
is used to add elements to a
Vector
. For example, the
following three statements add three objects to
d
, so Fig. 5.3 shows what
d
now
looks like.
a6
a1
Integer
4
Patient
0 6 1 8 2 4 3 ?
4 ?
a8
a4
size()
capacity()
etc.
String
String
"red"
"blue"
Figure 5.3:
A Vector with size 3 and capacity 5
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