79 lines
2.9 KiB
Java
79 lines
2.9 KiB
Java
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package java.util;
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public interface Queue<E> extends Collection<E> {
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/**
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* Inserts the specified element into this queue if it is possible to do so
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* immediately without violating capacity restrictions, returning
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* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
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* if no space is currently available.
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*
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* @param e the element to add
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* @return <tt>true</tt> (as specified by {@link Collection#add})
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* @throws IllegalStateException if the element cannot be added at this
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* time due to capacity restrictions
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* @throws ClassCastException if the class of the specified element
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* prevents it from being added to this queue
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* @throws NullPointerException if the specified element is null and
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* this queue does not permit null elements
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* @throws IllegalArgumentException if some property of this element
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* prevents it from being added to this queue
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*/
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boolean add(E e);
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/**
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* Inserts the specified element into this queue if it is possible to do
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* so immediately without violating capacity restrictions.
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* When using a capacity-restricted queue, this method is generally
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* preferable to {@link #add}, which can fail to insert an element only
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* by throwing an exception.
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*
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* @param e the element to add
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* @return <tt>true</tt> if the element was added to this queue, else
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* <tt>false</tt>
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* @throws ClassCastException if the class of the specified element
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* prevents it from being added to this queue
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* @throws NullPointerException if the specified element is null and
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* this queue does not permit null elements
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* @throws IllegalArgumentException if some property of this element
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* prevents it from being added to this queue
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*/
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boolean offer(E e);
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/**
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* Retrieves and removes the head of this queue. This method differs
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* from {@link #poll poll} only in that it throws an exception if this
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* queue is empty.
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*
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* @return the head of this queue
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* @throws NoSuchElementException if this queue is empty
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*/
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E remove();
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/**
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* Retrieves and removes the head of this queue,
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* or returns <tt>null</tt> if this queue is empty.
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*
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* @return the head of this queue, or <tt>null</tt> if this queue is empty
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*/
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E poll();
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/**
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* Retrieves, but does not remove, the head of this queue. This method
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* differs from {@link #peek peek} only in that it throws an exception
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* if this queue is empty.
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*
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* @return the head of this queue
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* @throws NoSuchElementException if this queue is empty
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*/
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E element();
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/**
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* Retrieves, but does not remove, the head of this queue,
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* or returns <tt>null</tt> if this queue is empty.
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*
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* @return the head of this queue, or <tt>null</tt> if this queue is empty
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*/
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E peek();
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}
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