Java Reference
In-Depth Information
5.3.3
Other methods in class Vector
Class
Vector
contains other methods that will help you create and maintain a list
of objects. The ones you are most likely to use are listed below. See lesson page
5-5 of the CD for more explanation, or look at the Java API specs for
Vector
.
When removing one or more elements from
v
, those with higher indices than
the removed ones are shifted down. Thus, the size of the
v
is reduced by the num-
ber of elements removed.
Activity
5-5.2
•
v.toString() =
a description of
v
of the form
[v[0], v[1], …]
.
•
v.contains(obj) =
“
obj
is an element of
v
”.
•
v.indexOf(obj) =
index of first object in
v
that equals
obj
(
-1
if none).
•
v.indexOf(obj, k) =
index of first object in v with index at least k
that equals
obj
(
-1
if none).
•
v.lastIndexOf(obj)=
index of last object in
v
that equals
obj
(
-1
if none).
•
v.lastIndexOf(obj, k)
=
index of last object in v with index at most k
that equals
obj
(
-1
if none).
•
v.remove(i)
Remove
v[i]
and return the removed element.
•
v.remove(obj)
Remove from
v
the first object that equals
obj
and return
the value of “an element was removed” (a boolean).
•
v.removeRange(i, j)
Remove
v[i..j]
from
v
.
•
v.clear();
Remove all objects from
v
, so that its size is
0
.
5.3.4
Exercises on class Vector
E1.
In the Interactions pane of DrJava, create a
Vector vec
—remember to
import
java.util.*
first— and add these strings to it:
"one"
,
"two"
,
"four"
.
Then, type the expression
vec
. What is its value? Next, execute the call:
vec.add(2, "three");
. Now, what is the value of expression
vec
?
E2.
In the Interactions pane of DrJava, create a
Vector v1
that contains the val-
ues of these expressions:
new
Integer(1)
,
new
Integer(3),
new
Integer(5).
Then, find out the value of expression
v1
. Write down the values of the follow-
ing expressions (let DrJava evaluate them):
v1.elementAt(1)
,
v1.elementAt(2)
, and
v1.size()
.
E3.
In the Interactions pane of DrJava, create a
Vector v1
that contains the val-
ues of these expressions:
new
Integer(1)
,
new
Integer(3),
new
Integer(5).
Then, find out the value of expression
v1
. What happens when you execute this
assignment statement, and what do you have to do to fix it?
Integer middle= v1.elementAt(1);
E4.
Write (and test) a boolean function with two arguments: a
Vector v
and an
Object x
. The function returns the value of the sentence “
x
occurs at least twice
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