org.apache.commons.collections

Class ArrayStack

public class ArrayStack extends ArrayList implements Buffer

An implementation of the java.util.Stack API that is based on an ArrayList instead of a Vector, so it is not synchronized to protect against multi-threaded access. The implementation is therefore operates faster in environments where you do not need to worry about multiple thread contention.

The removal order of an ArrayStack is based on insertion order: The most recently added element is removed first. The iteration order is not the same as the removal order. The iterator returns elements from the bottom up, whereas the remove method removes them from the top down.

Unlike Stack, ArrayStack accepts null entries.

Since: Commons Collections 1.0

Version: $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $

Author: Craig R. McClanahan Paul Jack Stephen Colebourne

See Also: java.util.Stack

Constructor Summary
	ArrayStack() Constructs a new empty `ArrayStack`.
	ArrayStack(int initialSize) Constructs a new empty `ArrayStack` with an initial size.

Method Summary
boolean	empty() Return `true` if this stack is currently empty.
Object	get() Returns the element on the top of the stack.
Object	peek() Returns the top item off of this stack without removing it.
Object	peek(int n) Returns the n'th item down (zero-relative) from the top of this stack without removing it.
Object	pop() Pops the top item off of this stack and return it.
Object	push(Object item) Pushes a new item onto the top of this stack.
Object	remove() Removes the element on the top of the stack.
int	search(Object object) Returns the one-based position of the distance from the top that the specified object exists on this stack, where the top-most element is considered to be at distance `1`.

Constructor Detail

ArrayStack

public ArrayStack()

Constructs a new empty ArrayStack. The initial size is controlled by ArrayList and is currently 10.

ArrayStack

public ArrayStack(int initialSize)

Constructs a new empty ArrayStack with an initial size.

Parameters: initialSize the initial size to use

Throws: IllegalArgumentException if the specified initial size is negative

Method Detail

empty

public boolean empty()

Return true if this stack is currently empty.

This method exists for compatibility with java.util.Stack. New users of this class should use isEmpty instead.

Returns: true if the stack is currently empty

get

public Object get()

Returns the element on the top of the stack.

Returns: the element on the top of the stack

Throws: BufferUnderflowException if the stack is empty

peek

public Object peek()

Returns the top item off of this stack without removing it.

Returns: the top item on the stack

Throws: EmptyStackException if the stack is empty

peek

public Object peek(int n)

Returns the n'th item down (zero-relative) from the top of this stack without removing it.

Parameters: n the number of items down to go

Returns: the n'th item on the stack, zero relative

Throws: EmptyStackException if there are not enough items on the stack to satisfy this request

pop

public Object pop()

Pops the top item off of this stack and return it.

Returns: the top item on the stack

Throws: EmptyStackException if the stack is empty

push

public Object push(Object item)

Pushes a new item onto the top of this stack. The pushed item is also returned. This is equivalent to calling add.

Parameters: item the item to be added

Returns: the item just pushed

remove

public Object remove()

Removes the element on the top of the stack.

Returns: the removed element

Throws: BufferUnderflowException if the stack is empty

search

public int search(Object object)

Returns the one-based position of the distance from the top that the specified object exists on this stack, where the top-most element is considered to be at distance 1. If the object is not present on the stack, return -1 instead. The equals() method is used to compare to the items in this stack.

Parameters: object the object to be searched for

Returns: the 1-based depth into the stack of the object, or -1 if not found