org.xerial.util.Deque Maven / Gradle / Ivy
/*
* @(#)Deque.java 1.5 06/04/21
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package org.xerial.util;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
/**
* A linear collection that supports element insertion and removal at both ends.
* The name deque is short for "double ended queue" and is usually
* pronounced "deck". Most Deque implementations place no fixed limits
* on the number of elements they may contain, but this interface supports
* capacity-restricted deques as well as those with no fixed size limit.
*
*
* This interface defines methods to access the elements at both ends of the
* deque. Methods are provided to insert, remove, and examine the element. Each
* of these methods exists in two forms: one throws an exception if the
* operation fails, the other returns a special value (either null or
* false, depending on the operation). The latter form of the insert
* operation is designed specifically for use with capacity-restricted
* Deque implementations; in most implementations, insert operations
* cannot fail.
*
*
* The twelve methods described above are summarized in the following table:
*
*
*
*
* First Element (Head)
* Last Element (Tail)
*
*
* Throws exception
* Special value
* Throws exception
* Special value
*
*
* Insert
* {@link #addFirst addFirst(e)}
* {@link #offerFirst offerFirst(e)}
* {@link #addLast addLast(e)}
* {@link #offerLast offerLast(e)}
*
*
* Remove
* {@link #removeFirst removeFirst()}
* {@link #pollFirst pollFirst()}
* {@link #removeLast removeLast()}
* {@link #pollLast pollLast()}
*
*
* Examine
* {@link #getFirst getFirst()}
* {@link #peekFirst peekFirst()}
* {@link #getLast getLast()}
* {@link #peekLast peekLast()}
*
*
*
*
* This interface extends the {@link Queue} interface. When a deque is used as a
* queue, FIFO (First-In-First-Out) behavior results. Elements are added at the
* end of the deque and removed from the beginning. The methods inherited from
* the Queue interface are precisely equivalent to Deque
* methods as indicated in the following table:
*
*
*
*
* Queue Method
* Equivalent Deque Method
*
*
* {@link java.util.Queue#add add(e)}
* {@link #addLast addLast(e)}
*
*
* {@link java.util.Queue#offer offer(e)}
* {@link #offerLast offerLast(e)}
*
*
* {@link java.util.Queue#remove remove()}
* {@link #removeFirst removeFirst()}
*
*
* {@link java.util.Queue#poll poll()}
* {@link #pollFirst pollFirst()}
*
*
* {@link java.util.Queue#element element()}
* {@link #getFirst getFirst()}
*
*
* {@link java.util.Queue#peek peek()}
* {@link #peek peekFirst()}
*
*
*
*
* Deques can also be used as LIFO (Last-In-First-Out) stacks. This interface
* should be used in preference to the legacy {@link Stack} class. When a deque
* is used as a stack, elements are pushed and popped from the beginning of the
* deque. Stack methods are precisely equivalent to Deque methods as
* indicated in the table below:
*
*
*
*
* Stack Method
* Equivalent Deque Method
*
*
* {@link #push push(e)}
* {@link #addFirst addFirst(e)}
*
*
* {@link #pop pop()}
* {@link #removeFirst removeFirst()}
*
*
* {@link #peek peek()}
* {@link #peekFirst peekFirst()}
*
*
*
*
* Note that the {@link #peek peek} method works equally well when a deque is
* used as a queue or a stack; in either case, elements are drawn from the
* beginning of the deque.
*
*
* This interface provides two methods to remove interior elements,
* {@link #removeFirstOccurrence removeFirstOccurrence} and
* {@link #removeLastOccurrence removeLastOccurrence}.
*
*
* Unlike the {@link List} interface, this interface does not provide support
* for indexed access to elements.
*
*
* While Deque implementations are not strictly required to prohibit
* the insertion of null elements, they are strongly encouraged to do so. Users
* of any Deque implementations that do allow null elements are
* strongly encouraged not to take advantage of the ability to insert
* nulls. This is so because null is used as a special return value by
* various methods to indicated that the deque is empty.
*
*
* Deque implementations generally do not define element-based versions
* of the equals and hashCode methods, but instead inherit the
* identity-based versions from class Object.
*
*
* This interface is a member of the Java Collections Framework.
*
* @author Doug Lea
* @author Josh Bloch
* @since 1.6
* @param
* the type of elements held in this collection
*/
public interface Deque extends Queue
{
/**
* Inserts the specified element at the front of this deque if it is
* possible to do so immediately without violating capacity restrictions.
* When using a capacity-restricted deque, it is generally preferable to use
* method {@link #offerFirst}.
*
* @param e
* the element to 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 deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
void addFirst(E e);
/**
* Inserts the specified element at the end of this deque if it is possible
* to do so immediately without violating capacity restrictions. When using
* a capacity-restricted deque, it is generally preferable to use method
* {@link #offerLast}.
*
*
* This method is equivalent to {@link #add}.
*
* @param e
* the element to 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 deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
void addLast(E e);
/**
* Inserts the specified element at the front of this deque unless it would
* violate capacity restrictions. When using a capacity-restricted deque,
* this method is generally preferable to the {@link #addFirst} method,
* which can fail to insert an element only by throwing an exception.
*
* @param e
* the element to add
* @return true if the element was added to this deque, else
* false
* @throws ClassCastException
* if the class of the specified element prevents it from being
* added to this deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
boolean offerFirst(E e);
/**
* Inserts the specified element at the end of this deque unless it would
* violate capacity restrictions. When using a capacity-restricted deque,
* this method is generally preferable to the {@link #addLast} method, which
* can fail to insert an element only by throwing an exception.
*
* @param e
* the element to add
* @return true if the element was added to this deque, else
* false
* @throws ClassCastException
* if the class of the specified element prevents it from being
* added to this deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
boolean offerLast(E e);
/**
* Retrieves and removes the first element of this deque. This method
* differs from {@link #pollFirst pollFirst} only in that it throws an
* exception if this deque is empty.
*
* @return the head of this deque
* @throws NoSuchElementException
* if this deque is empty
*/
E removeFirst();
/**
* Retrieves and removes the last element of this deque. This method differs
* from {@link #pollLast pollLast} only in that it throws an exception if
* this deque is empty.
*
* @return the tail of this deque
* @throws NoSuchElementException
* if this deque is empty
*/
E removeLast();
/**
* Retrieves and removes the first element of this deque, or returns
* null if this deque is empty.
*
* @return the head of this deque, or null if this deque is empty
*/
E pollFirst();
/**
* Retrieves and removes the last element of this deque, or returns
* null if this deque is empty.
*
* @return the tail of this deque, or null if this deque is empty
*/
E pollLast();
/**
* Retrieves, but does not remove, the first element of this deque.
*
* This method differs from {@link #peekFirst peekFirst} only in that it
* throws an exception if this deque is empty.
*
* @return the head of this deque
* @throws NoSuchElementException
* if this deque is empty
*/
E getFirst();
/**
* Retrieves, but does not remove, the last element of this deque. This
* method differs from {@link #peekLast peekLast} only in that it throws an
* exception if this deque is empty.
*
* @return the tail of this deque
* @throws NoSuchElementException
* if this deque is empty
*/
E getLast();
/**
* Retrieves, but does not remove, the first element of this deque, or
* returns null if this deque is empty.
*
* @return the head of this deque, or null if this deque is empty
*/
E peekFirst();
/**
* Retrieves, but does not remove, the last element of this deque, or
* returns null if this deque is empty.
*
* @return the tail of this deque, or null if this deque is empty
*/
E peekLast();
/**
* Removes the first occurrence of the specified element from this deque. If
* the deque does not contain the element, it is unchanged. More formally,
* removes the first element e such that
* (o==null ? e==null : o.equals(e)) (if such
* an element exists). Returns true if this deque contained the
* specified element (or equivalently, if this deque changed as a result of
* the call).
*
* @param o
* element to be removed from this deque, if present
* @return true if an element was removed as a result of this call
* @throws ClassCastException
* if the class of the specified element is incompatible with
* this deque (optional)
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements (optional)
*/
boolean removeFirstOccurrence(Object o);
/**
* Removes the last occurrence of the specified element from this deque. If
* the deque does not contain the element, it is unchanged. More formally,
* removes the last element e such that
* (o==null ? e==null : o.equals(e)) (if such
* an element exists). Returns true if this deque contained the
* specified element (or equivalently, if this deque changed as a result of
* the call).
*
* @param o
* element to be removed from this deque, if present
* @return true if an element was removed as a result of this call
* @throws ClassCastException
* if the class of the specified element is incompatible with
* this deque (optional)
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements (optional)
*/
boolean removeLastOccurrence(Object o);
// *** Queue methods ***
/**
* Inserts the specified element into the queue represented by this deque
* (in other words, at the tail of this deque) 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. When using a capacity-restricted
* deque, it is generally preferable to use {@link #offer(Object) offer}.
*
*
* This method is equivalent to {@link #addLast}.
*
* @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 deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
boolean add(E e);
/**
* Inserts the specified element into the queue represented by this deque
* (in other words, at the tail of this deque) if it is possible to do so
* immediately without violating capacity restrictions, returning
* true upon success and false if no space is currently
* available. When using a capacity-restricted deque, this method is
* generally preferable to the {@link #add} method, which can fail to insert
* an element only by throwing an exception.
*
*
* This method is equivalent to {@link #offerLast}.
*
* @param e
* the element to add
* @return true if the element was added to this deque, else
* false
* @throws ClassCastException
* if the class of the specified element prevents it from being
* added to this deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
boolean offer(E e);
/**
* Retrieves and removes the head of the queue represented by this deque (in
* other words, the first element of this deque). This method differs from
* {@link #poll poll} only in that it throws an exception if this deque is
* empty.
*
*
* This method is equivalent to {@link #removeFirst()}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException
* if this deque is empty
*/
E remove();
/**
* Retrieves and removes the head of the queue represented by this deque (in
* other words, the first element of this deque), or returns null
* if this deque is empty.
*
*
* This method is equivalent to {@link #pollFirst()}.
*
* @return the first element of this deque, or null if this deque
* is empty
*/
E poll();
/**
* Retrieves, but does not remove, the head of the queue represented by this
* deque (in other words, the first element of this deque). This method
* differs from {@link #peek peek} only in that it throws an exception if
* this deque is empty.
*
*
* This method is equivalent to {@link #getFirst()}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException
* if this deque is empty
*/
E element();
/**
* Retrieves, but does not remove, the head of the queue represented by this
* deque (in other words, the first element of this deque), or returns
* null if this deque is empty.
*
*
* This method is equivalent to {@link #peekFirst()}.
*
* @return the head of the queue represented by this deque, or null
* if this deque is empty
*/
E peek();
// *** Stack methods ***
/**
* Pushes an element onto the stack represented by this deque (in other
* words, at the head of this deque) 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 method is equivalent to {@link #addFirst}.
*
* @param e
* the element to push
* @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 deque
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements
* @throws IllegalArgumentException
* if some property of the specified element prevents it from
* being added to this deque
*/
void push(E e);
/**
* Pops an element from the stack represented by this deque. In other words,
* removes and returns the first element of this deque.
*
*
* This method is equivalent to {@link #removeFirst()}.
*
* @return the element at the front of this deque (which is the top of the
* stack represented by this deque)
* @throws NoSuchElementException
* if this deque is empty
*/
E pop();
// *** Collection methods ***
/**
* Removes the first occurrence of the specified element from this deque. If
* the deque does not contain the element, it is unchanged. More formally,
* removes the first element e such that
* (o==null ? e==null : o.equals(e)) (if such
* an element exists). Returns true if this deque contained the
* specified element (or equivalently, if this deque changed as a result of
* the call).
*
*
* This method is equivalent to {@link #removeFirstOccurrence}.
*
* @param o
* element to be removed from this deque, if present
* @return true if an element was removed as a result of this call
* @throws ClassCastException
* if the class of the specified element is incompatible with
* this deque (optional)
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements (optional)
*/
boolean remove(Object o);
/**
* Returns true if this deque contains the specified element. More
* formally, returns true if and only if this deque contains at
* least one element e such that
* (o==null ? e==null : o.equals(e)).
*
* @param o
* element whose presence in this deque is to be tested
* @return true if this deque contains the specified element
* @throws ClassCastException
* if the type of the specified element is incompatible with
* this deque (optional)
* @throws NullPointerException
* if the specified element is null and this deque does not
* permit null elements (optional)
*/
boolean contains(Object o);
/**
* Returns the number of elements in this deque.
*
* @return the number of elements in this deque
*/
public int size();
/**
* Returns an iterator over the elements in this deque in proper sequence.
* The elements will be returned in order from first (head) to last (tail).
*
* @return an iterator over the elements in this deque in proper sequence
*/
Iterator iterator();
/**
* Returns an iterator over the elements in this deque in reverse sequential
* order. The elements will be returned in order from last (tail) to first
* (head).
*
* @return an iterator over the elements in this deque in reverse sequence
*/
Iterator descendingIterator();
}