Java Reference
In-Depth Information
Each iteration will search
transactions
from the element given by the index stored in the variable
position
. The initial value of
-1
is incremented in the
while
loop condition, so on the first iteration it is 0.
On subsequent iterations where
indexOf()
finds an occurrence of
aTransaction
, the loop condition
increments
position
to the next element ready for the next search. When no further references to the
object can be found from the position specified by the second argument, the method
indexOf()
will return
-1 and the loop will end by executing the break statement. If
aTransaction
happens to be found in the
last element in the
Vector
at index position
size-1
, the value of position will be incremented to
size
by
the loop condition expression, so the expression will be
false
and the loop will end.
Applying Vectors
Let's implement a simple example to see how using a
Vector
works out in practice. We will write a
program to model a collection of people, where we can add the names of the persons that we want in
the crowd from the keyboard. We'll first define a class to represent a person:
public class Person {
// Constructor
public Person(String firstName, String surname) {
this.firstName = firstName;
this.surname = surname;
}
public String toString() {
return firstName + " " + surname;
}
private String firstName; // First name of person
private String surname; // Second name of person
}
The only data members are the
String
members to store the first and second names for a person. By
overriding the default implementation of the
toString()
method, provided by the
Object
class, we
allow objects of the
Person
class to be used as arguments to the
println()
method for output, since
as you are well aware by now,
toString()
will be automatically invoked in this case.
Now we can define a class that will represent a crowd. We could just create a
Vector
object in
main()
but
this would mean any type of object could be stored. By defining our own class we can ensure that only
Person
objects can be stored in the
Vector
and in this way make our program less prone to errors.
The class definition representing a crowd is:
import java.util.*;
class Crowd {
// Constructors
public Crowd() {
// Create default Vector object to hold people
people = new Vector();
}
public Crowd(int numPersons) {
