uk.org.ogsadai.common
Class FIFOQueue

java.lang.Object
  |
  +--uk.org.ogsadai.common.FIFOQueue

All Implemented Interfaces:

Queue

public class FIFOQueue

extends java.lang.Object

implements Queue

Array-based implementation of the uk.org.ogsadai.common.Queue interface, using a first-in-first-out (FIFO) ordering of elements.

• This implementation is not thread-safe and should be 'wrapped' accordingly when accessed by multiple threads.
• No element in this queue may be null.
• The capacity of the queue remains fixed throughout the queue's lifetime. Capacity is configurable at construction time and limited to a maximum of java.lang.Integer.MAX_VALUE elements.
• The default capacity is given by DEFAULT_CAPACITY.

Author:

The OGSA-DAI Project team

See Also:

Queue

COPYRIGHT_NOTICE

private static final java.lang.String COPYRIGHT_NOTICE

See Also:

Constant Field Values

DEFAULT_CAPACITY

public static final int DEFAULT_CAPACITY

Default fixed capacity.

See Also:

Constant Field Values

mData

protected final java.lang.Object[] mData

Array containing elements of the queue.

mCapacity

protected int mCapacity

Capacity of the queue.

mSize

private int mSize

mHeadIndex

private int mHeadIndex

mTailIndex

private int mTailIndex

mModificationCount

private long mModificationCount

FIFOQueue

public FIFOQueue(int capacity)
          throws java.lang.IllegalArgumentException

Constructs a queue of given, fixed capacity.

Parameters:

capacity - The desired capacity, which must be greater than 1.

Throws:

java.lang.IllegalArgumentException - If the supplied capacity argument is less than 1.

FIFOQueue

public FIFOQueue()

Constructs a queue with a default capacity of DEFAULT_CAPACITY elements.

offer

public boolean offer(java.lang.Object obj)
              throws java.lang.IllegalArgumentException

Description copied from interface: Queue

Inserts, if possible, an object into the queue.

Specified by:

offer in interface Queue

Parameters:

obj - The item to insert. Must not be null.

Returns:

true if it was possible to add the element to this queue, otherwise false.

java.lang.IllegalArgumentException

poll

public java.lang.Object poll()

Description copied from interface: Queue

Retrieves and removes the head of the queue.

Specified by:

poll in interface Queue

Returns:

the head of the queue, or null if the queue is empty.

remove

public java.lang.Object remove()
                        throws java.util.NoSuchElementException

Description copied from interface: Queue

Retrieves and removes the head of the queue. Unlike poll, which performs a similar task, this method throws an exception if called on an empty queue.

Specified by:

remove in interface Queue

Returns:

the head of the queue.

Throws:

java.util.NoSuchElementException - if this queue is empty.

remove

public void remove(java.lang.Object item)
            throws java.util.NoSuchElementException

Description copied from interface: Queue

Removes the specified item from the queue.

Specified by:

remove in interface Queue

Parameters:

item - The item to remove.

Throws:

java.util.NoSuchElementException - if this queue is empty.

peek

public java.lang.Object peek()

Description copied from interface: Queue

Retrieves the head of the queue without removing it.

Specified by:

peek in interface Queue

Returns:

the head of this queue, or null if the queue is empty.

element

public java.lang.Object element()
                         throws java.util.NoSuchElementException

Description copied from interface: Queue

Retrieves the head of the queue without removing it. Unlike peek, which performs a similar task, this method throws an exception if called on an empty queue.

Specified by:

element in interface Queue

Returns:

the head of this queue.

Throws:

java.util.NoSuchElementException - if this queue is empty.

size

public int size()

Description copied from interface: Queue

Returns the number of elements in this queue.

Specified by:

size in interface Queue

Returns:

the number of elements in the queue.

iterator

public java.util.Iterator iterator()

Description copied from interface: Queue

Returns an iterator over the elements in this queue. The order of iteration is the same as the order of the elements in the queue at the time this method is called.

Specified by:

iterator in interface Queue

Returns:

an iterator over the elements in the queue.

inc

private final int inc(int index)

Circularly increase indices into data array.

Parameters:

index - Update index. If it reaches capacity then circle back to the beginning of the queue.

Returns:

new index.

dec

private final int dec(int index)

Circularly decrease indices into data array

Parameters:

index - Update index. If it reaches 0 then circle on to the end of the queue.

Returns:

new index.