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Java/DataStructures/Queues/Queues.java at master · null-exception/Java · GitHub
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Queues
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Queues.java
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package
DataStructures
.
Queues
;
/**
* This implements Queues by using the class Queue.
* <p>
* A queue data structure functions the same as a real world queue.
* The elements that are added first are the first to be removed.
* New elements are added to the back/rear of the queue.
*
*/
class
Queue
{
/**
* Default initial capacity.
*/
private
static
final
int
DEFAULT_CAPACITY
=
10
;
/**
* Max size of the queue
*/
private
int
maxSize
;
/**
* The array representing the queue
*/
private
int
[]
queueArray
;
/**
* Front of the queue
*/
private
int
front
;
/**
* Rear of the queue
*/
private
int
rear
;
/**
* How many items are in the queue
*/
private
int
nItems
;
/**
* init with DEFAULT_CAPACITY
*/
public
Queue
() {
this
(
DEFAULT_CAPACITY
);
}
/**
* Constructor
*
* @param size Size of the new queue
*/
public
Queue
(
int
size
) {
maxSize
=
size
;
queueArray
=
new
int
[
size
];
front
=
0
;
rear
= -
1
;
nItems
=
0
;
}
/**
* Inserts an element at the rear of the queue
*
* @param x element to be added
* @return True if the element was added successfully
*/
public
boolean
insert
(
int
x
) {
if
(
isFull
())
return
false
;
// If the back of the queue is the end of the array wrap around to the front
rear
= (
rear
+
1
) %
maxSize
;
queueArray
[
rear
] =
x
;
nItems
++;
return
true
;
}
/**
* Remove an element from the front of the queue
*
* @return the new front of the queue
*/
public
int
remove
() {
if
(
isEmpty
()) {
return
-
1
;
}
int
temp
=
queueArray
[
front
];
front
= (
front
+
1
) %
maxSize
;
nItems
--;
return
temp
;
}
/**
* Checks what's at the front of the queue
*
* @return element at the front of the queue
*/
public
int
peekFront
() {
return
queueArray
[
front
];
}
/**
* Checks what's at the rear of the queue
*
* @return element at the rear of the queue
*/
public
int
peekRear
() {
return
queueArray
[
rear
];
}
/**
* Returns true if the queue is empty
*
* @return true if the queue is empty
*/
public
boolean
isEmpty
() {
return
nItems
==
0
;
}
/**
* Returns true if the queue is full
*
* @return true if the queue is full
*/
public
boolean
isFull
() {
return
nItems
==
maxSize
;
}
/**
* Returns the number of elements in the queue
*
* @return number of elements in the queue
*/
public
int
getSize
() {
return
nItems
;
}
@
Override
public
String
toString
() {
StringBuilder
sb
=
new
StringBuilder
();
sb
.
append
(
"["
);
for
(
int
i
=
front
; ;
i
= ++
i
%
maxSize
) {
sb
.
append
(
queueArray
[
i
]).
append
(
", "
);
if
(
i
==
rear
) {
break
;
}
}
sb
.
replace
(
sb
.
length
() -
2
,
sb
.
length
(),
"]"
);
return
sb
.
toString
();
}
}
/**
* This class is the example for the Queue class
*
* @author Unknown
*/
public
class
Queues
{
/**
* Main method
*
* @param args Command line arguments
*/
public
static
void
main
(
String
[]
args
) {
Queue
myQueue
=
new
Queue
(
4
);
myQueue
.
insert
(
10
);
myQueue
.
insert
(
2
);
myQueue
.
insert
(
5
);
myQueue
.
insert
(
3
);
// [10(front), 2, 5, 3(rear)]
System
.
out
.
println
(
myQueue
.
isFull
());
// Will print true
myQueue
.
remove
();
// Will make 2 the new front, making 10 no longer part of the queue
// [10, 2(front), 5, 3(rear)]
myQueue
.
insert
(
7
);
// Insert 7 at the rear which will be index 0 because of wrap around
// [7(rear), 2(front), 5, 3]
System
.
out
.
println
(
myQueue
.
peekFront
());
// Will print 2
System
.
out
.
println
(
myQueue
.
peekRear
());
// Will print 7
System
.
out
.
println
(
myQueue
.
toString
());
// Will print [2, 5, 3, 7]
}
}
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