java.util.AbstractQueue Maven / Gradle / Ivy
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* published by the Free Software Foundation. Oracle designates this
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*
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*
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/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util;
/**
* This class provides skeletal implementations of some {@link Queue}
* operations. The implementations in this class are appropriate when
* the base implementation does not allow null
* elements. Methods {@link #add add}, {@link #remove remove}, and
* {@link #element element} are based on {@link #offer offer}, {@link
* #poll poll}, and {@link #peek peek}, respectively, but throw
* exceptions instead of indicating failure via false or
* null returns.
*
* A Queue implementation that extends this class must
* minimally define a method {@link Queue#offer} which does not permit
* insertion of null elements, along with methods {@link
* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
* {@link Collection#iterator}. Typically, additional methods will be
* overridden as well. If these requirements cannot be met, consider
* instead subclassing {@link AbstractCollection}.
*
*
This class is a member of the
*
* Java Collections Framework.
*
* @since 1.5
* @author Doug Lea
* @param the type of elements held in this collection
*/
public abstract class AbstractQueue
extends AbstractCollection
implements Queue {
/**
* Constructor for use by subclasses.
*/
protected AbstractQueue() {
}
/**
* Inserts the specified element into this queue if it is possible to do so
* immediately without violating capacity restrictions, returning
* true upon success and throwing an IllegalStateException
* if no space is currently available.
*
* This implementation returns true if offer succeeds,
* else throws an IllegalStateException.
*
* @param e the element to add
* @return true (as specified by {@link Collection#add})
* @throws IllegalStateException if the element cannot be added at this
* time due to capacity restrictions
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null and
* this queue does not permit null elements
* @throws IllegalArgumentException if some property of this element
* prevents it from being added to this queue
*/
public boolean add(E e) {
if (offer(e))
return true;
else
throw new IllegalStateException("Queue full");
}
/**
* Retrieves and removes the head of this queue. This method differs
* from {@link #poll poll} only in that it throws an exception if this
* queue is empty.
*
*
This implementation returns the result of poll
* unless the queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
public E remove() {
E x = poll();
if (x != null)
return x;
else
throw new NoSuchElementException();
}
/**
* Retrieves, but does not remove, the head of this queue. This method
* differs from {@link #peek peek} only in that it throws an exception if
* this queue is empty.
*
*
This implementation returns the result of peek
* unless the queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
public E element() {
E x = peek();
if (x != null)
return x;
else
throw new NoSuchElementException();
}
/**
* Removes all of the elements from this queue.
* The queue will be empty after this call returns.
*
*
This implementation repeatedly invokes {@link #poll poll} until it
* returns null.
*/
public void clear() {
while (poll() != null)
;
}
/**
* Adds all of the elements in the specified collection to this
* queue. Attempts to addAll of a queue to itself result in
* IllegalArgumentException. Further, the behavior of
* this operation is undefined if the specified collection is
* modified while the operation is in progress.
*
*
This implementation iterates over the specified collection,
* and adds each element returned by the iterator to this
* queue, in turn. A runtime exception encountered while
* trying to add an element (including, in particular, a
* null element) may result in only some of the elements
* having been successfully added when the associated exception is
* thrown.
*
* @param c collection containing elements to be added to this queue
* @return true if this queue changed as a result of the call
* @throws ClassCastException if the class of an element of the specified
* collection prevents it from being added to this queue
* @throws NullPointerException if the specified collection contains a
* null element and this queue does not permit null elements,
* or if the specified collection is null
* @throws IllegalArgumentException if some property of an element of the
* specified collection prevents it from being added to this
* queue, or if the specified collection is this queue
* @throws IllegalStateException if not all the elements can be added at
* this time due to insertion restrictions
* @see #add(Object)
*/
public boolean addAll(Collection c) {
if (c == null)
throw new NullPointerException();
if (c == this)
throw new IllegalArgumentException();
boolean modified = false;
for (E e : c)
if (add(e))
modified = true;
return modified;
}
}