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package java.util;

public interface Queue<E> extends Collection<E> {

/**

* Inserts the specified element into this queue if it is possible to do so

* immediately without violating capacity restrictions, returning

* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>

* if no space is currently available.

*

* @param e the element to add

* @return <tt>true</tt> (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

*/

boolean add(E e);

/**

* Inserts the specified element into this queue if it is possible to do

* so immediately without violating capacity restrictions.

* When using a capacity-restricted queue, this method is generally

* preferable to {@link #add}, which can fail to insert an element only

* by throwing an exception.

*

* @param e the element to add

* @return <tt>true</tt> if the element was added to this queue, else

* <tt>false</tt>

* @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

*/

boolean offer(E e);

/**

* 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.

*

* @return the head of this queue

* @throws NoSuchElementException if this queue is empty

*/

E remove();

/**

* Retrieves and removes the head of this queue,

* or returns <tt>null</tt> if this queue is empty.

*

* @return the head of this queue, or <tt>null</tt> if this queue is empty

*/

E poll();

/**

* 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.

*

* @return the head of this queue

* @throws NoSuchElementException if this queue is empty

*/

E element();

/**

* Retrieves, but does not remove, the head of this queue,

* or returns <tt>null</tt> if this queue is empty.

*

* @return the head of this queue, or <tt>null</tt> if this queue is empty

*/

E peek();

}