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/* * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Sun designates this * particular file as subject to the "Classpath" exception as provided * by Sun in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. */ package java.util; /** * Linked list implementation of the <tt>List</tt> interface. Implements all * optional list operations, and permits all elements (including * <tt>null</tt>). In addition to implementing the <tt>List</tt> interface, * the <tt>LinkedList</tt> class provides uniformly named methods to * <tt>get</tt>, <tt>remove</tt> and <tt>insert</tt> an element at the * beginning and end of the list. These operations allow linked lists to be * used as a stack, [email protected] Queue queue}, or [email protected] Deque * double-ended queue}. <p> * * The class implements the <tt>Deque</tt> interface, providing * first-in-first-out queue operations for <tt>add</tt>, * <tt>poll</tt>, along with other stack and deque operations.<p> * * All of the operations perform as could be expected for a doubly-linked * list. Operations that index into the list will traverse the list from * the beginning or the end, whichever is closer to the specified index.<p> * * <p><strong>Note that this implementation is not synchronized.</strong> * If multiple threads access a linked list concurrently, and at least * one of the threads modifies the list structurally, it <i>must</i> be * synchronized externally. (A structural modification is any operation * that adds or deletes one or more elements; merely setting the value of * an element is not a structural modification.) This is typically * accomplished by synchronizing on some object that naturally * encapsulates the list. * * If no such object exists, the list should be "wrapped" using the * [email protected] Collections#synchronizedList Collections.synchronizedList} * method. This is best done at creation time, to prevent accidental * unsynchronized access to the list:<pre> * List list = Collections.synchronizedList(new LinkedList(...));</pre> * * <p>The iterators returned by this class's <tt>iterator</tt> and * <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is * structurally modified at any time after the iterator is created, in * any way except through the Iterator's own <tt>remove</tt> or * <tt>add</tt> methods, the iterator will throw a [email protected] * ConcurrentModificationException}. Thus, in the face of concurrent * modification, the iterator fails quickly and cleanly, rather than * risking arbitrary, non-deterministic behavior at an undetermined * time in the future. * * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed * as it is, generally speaking, impossible to make any hard guarantees in the * presence of unsynchronized concurrent modification. Fail-fast iterators * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: <i>the fail-fast behavior of iterators * should be used only to detect bugs.</i> * * <p>This class is a member of the * <a href="[email protected]}/../technotes/guides/collections/index.html"> * Java Collections Framework</a>. * * @author Josh Bloch * @see List * @see ArrayList * @see Vector * @since 1.2 * @param <E> the type of elements held in this collection */ public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable { private transient Entry<E> header = new Entry<E>(null, null, null); private transient int size = 0; /** * Constructs an empty list. */ public LinkedList() { header.next = header.previous = header; } /** * Constructs a list containing the elements of the specified * collection, in the order they are returned by the collection's * iterator. * * @param c the collection whose elements are to be placed into this list * @throws NullPointerException if the specified collection is null */ public LinkedList(Collection<? extends E> c) { this(); addAll(c); } /** * Returns the first element in this list. * * @return the first element in this list * @throws NoSuchElementException if this list is empty */ public E getFirst() { if (size==0) throw new NoSuchElementException(); return header.next.element; } /** * Returns the last element in this list. * * @return the last element in this list * @throws NoSuchElementException if this list is empty */ public E getLast() { if (size==0) throw new NoSuchElementException(); return header.previous.element; } /** * Removes and returns the first element from this list. * * @return the first element from this list * @throws NoSuchElementException if this list is empty */ public E removeFirst() { return remove(header.next); } /** * Removes and returns the last element from this list. * * @return the last element from this list * @throws NoSuchElementException if this list is empty */ public E removeLast() { return remove(header.previous); } /** * Inserts the specified element at the beginning of this list. * * @param e the element to add */ public void addFirst(E e) { addBefore(e, header.next); } /** * Appends the specified element to the end of this list. * * <p>This method is equivalent to [email protected] #add}. * * @param e the element to add */ public void addLast(E e) { addBefore(e, header); } /** * Returns <tt>true</tt> if this list contains the specified element. * More formally, returns <tt>true</tt> if and only if this list contains * at least one element <tt>e</tt> such that * <tt>(o==null ? e==null : o.equals(e))</tt>. * * @param o element whose presence in this list is to be tested * @return <tt>true</tt> if this list contains the specified element */ public boolean contains(Object o) { return indexOf(o) != -1; } /** * Returns the number of elements in this list. * * @return the number of elements in this list */ public int size() { return size; } /** * Appends the specified element to the end of this list. * * <p>This method is equivalent to [email protected] #addLast}. * * @param e element to be appended to this list * @return <tt>true</tt> (as specified by [email protected] Collection#add}) */ public boolean add(E e) { addBefore(e, header); return true; } /** * Removes the first occurrence of the specified element from this list, * if it is present. If this list does not contain the element, it is * unchanged. More formally, removes the element with the lowest index * <tt>i</tt> such that * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> * (if such an element exists). Returns <tt>true</tt> if this list * contained the specified element (or equivalently, if this list * changed as a result of the call). * * @param o element to be removed from this list, if present * @return <tt>true</tt> if this list contained the specified element */ public boolean remove(Object o) { if (o==null) { for (Entry<E> e = header.next; e != header; e = e.next) { if (e.element==null) { remove(e); return true; } } } else { for (Entry<E> e = header.next; e != header; e = e.next) { if (o.equals(e.element)) { remove(e); return true; } } } return false; } /** * Appends all of the elements in the specified collection to the end of * this list, in the order that they are returned by the specified * collection's iterator. The behavior of this operation is undefined if * the specified collection is modified while the operation is in * progress. (Note that this will occur if the specified collection is * this list, and it's nonempty.) * * @param c collection containing elements to be added to this list * @return <tt>true</tt> if this list changed as a result of the call * @throws NullPointerException if the specified collection is null */ public boolean addAll(Collection<? extends E> c) { return addAll(size, c); } /** * Inserts all of the elements in the specified collection into this * list, starting at the specified position. Shifts the element * currently at that position (if any) and any subsequent elements to * the right (increases their indices). The new elements will appear * in the list in the order that they are returned by the * specified collection's iterator. * * @param index index at which to insert the first element * from the specified collection * @param c collection containing elements to be added to this list * @return <tt>true</tt> if this list changed as a result of the call * @throws IndexOutOfBoundsException [email protected]} * @throws NullPointerException if the specified collection is null */ public boolean addAll(int index, Collection<? extends E> c) { if (index < 0 || index > size) throw new IndexOutOfBoundsException("Index: "+index+ ", Size: "+size); Object[] a = c.toArray(); int numNew = a.length; if (numNew==0) return false; modCount++; Entry<E> successor = (index==size ? header : entry(index)); Entry<E> predecessor = successor.previous; for (int i=0; i<numNew; i++) { Entry<E> e = new Entry<E>((E)a[i], successor, predecessor); predecessor.next = e; predecessor = e; } successor.previous = predecessor; size += numNew; return true; } /** * Removes all of the elements from this list. */ public void clear() { Entry<E> e = header.next; while (e != header) { Entry<E> next = e.next; e.next = e.previous = null; e.element = null; e = next; } header.next = header.previous = header; size = 0; modCount++; } // Positional Access Operations /** * Returns the element at the specified position in this list. * * @param index index of the element to return * @return the element at the specified position in this list * @throws IndexOutOfBoundsException [email protected]} */ public E get(int index) { return entry(index).element; } /** * Replaces the element at the specified position in this list with the * specified element. * * @param index index of the element to replace * @param element element to be stored at the specified position * @return the element previously at the specified position * @throws IndexOutOfBoundsException [email protected]} */ public E set(int index, E element) { Entry<E> e = entry(index); E oldVal = e.element; e.element = element; return oldVal; } /** * Inserts the specified element at the specified position in this list. * Shifts the element currently at that position (if any) and any * subsequent elements to the right (adds one to their indices). * * @param index index at which the specified element is to be inserted * @param element element to be inserted * @throws IndexOutOfBoundsException [email protected]} */ public void add(int index, E element) { addBefore(element, (index==size ? header : entry(index))); } /** * Removes the element at the specified position in this list. Shifts any * subsequent elements to the left (subtracts one from their indices). * Returns the element that was removed from the list. * * @param index the index of the element to be removed * @return the element previously at the specified position * @throws IndexOutOfBoundsException [email protected]} */ public E remove(int index) { return remove(entry(index)); } /** * Returns the indexed entry. */ private Entry<E> entry(int index) { if (index < 0 || index >= size) throw new IndexOutOfBoundsException("Index: "+index+ ", Size: "+size); Entry<E> e = header; if (index < (size >> 1)) { for (int i = 0; i <= index; i++) e = e.next; } else { for (int i = size; i > index; i--) e = e.previous; } return e; } // Search Operations /** * Returns the index of the first occurrence of the specified element * in this list, or -1 if this list does not contain the element. * More formally, returns the lowest index <tt>i</tt> such that * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, * or -1 if there is no such index. * * @param o element to search for * @return the index of the first occurrence of the specified element in * this list, or -1 if this list does not contain the element */ public int indexOf(Object o) { int index = 0; if (o==null) { for (Entry e = header.next; e != header; e = e.next) { if (e.element==null) return index; index++; } } else { for (Entry e = header.next; e != header; e = e.next) { if (o.equals(e.element)) return index; index++; } } return -1; } /** * Returns the index of the last occurrence of the specified element * in this list, or -1 if this list does not contain the element. * More formally, returns the highest index <tt>i</tt> such that * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, * or -1 if there is no such index. * * @param o element to search for * @return the index of the last occurrence of the specified element in * this list, or -1 if this list does not contain the element */ public int lastIndexOf(Object o) { int index = size; if (o==null) { for (Entry e = header.previous; e != header; e = e.previous) { index--; if (e.element==null) return index; } } else { for (Entry e = header.previous; e != header; e = e.previous) { index--; if (o.equals(e.element)) return index; } } return -1; } // Queue operations. /** * Retrieves, but does not remove, the head (first element) of this list. * @return the head of this list, or <tt>null</tt> if this list is empty * @since 1.5 */ public E peek() { if (size==0) return null; return getFirst(); } /** * Retrieves, but does not remove, the head (first element) of this list. * @return the head of this list * @throws NoSuchElementException if this list is empty * @since 1.5 */ public E element() { return getFirst(); } /** * Retrieves and removes the head (first element) of this list * @return the head of this list, or <tt>null</tt> if this list is empty * @since 1.5 */ public E poll() { if (size==0) return null; return removeFirst(); } /** * Retrieves and removes the head (first element) of this list. * * @return the head of this list * @throws NoSuchElementException if this list is empty * @since 1.5 */ public E remove() { return removeFirst(); } /** * Adds the specified element as the tail (last element) of this list. * * @param e the element to add * @return <tt>true</tt> (as specified by [email protected] Queue#offer}) * @since 1.5 */ public boolean offer(E e) { return add(e); } // Deque operations /** * Inserts the specified element at the front of this list. * * @param e the element to insert * @return <tt>true</tt> (as specified by [email protected] Deque#offerFirst}) * @since 1.6 */ public boolean offerFirst(E e) { addFirst(e); return true; } /** * Inserts the specified element at the end of this list. * * @param e the element to insert * @return <tt>true</tt> (as specified by [email protected] Deque#offerLast}) * @since 1.6 */ public boolean offerLast(E e) { addLast(e); return true; } /** * Retrieves, but does not remove, the first element of this list, * or returns <tt>null</tt> if this list is empty. * * @return the first element of this list, or <tt>null</tt> * if this list is empty * @since 1.6 */ public E peekFirst() { if (size==0) return null; return getFirst(); } /** * Retrieves, but does not remove, the last element of this list, * or returns <tt>null</tt> if this list is empty. * * @return the last element of this list, or <tt>null</tt> * if this list is empty * @since 1.6 */ public E peekLast() { if (size==0) return null; return getLast(); } /** * Retrieves and removes the first element of this list, * or returns <tt>null</tt> if this list is empty. * * @return the first element of this list, or <tt>null</tt> if * this list is empty * @since 1.6 */ public E pollFirst() { if (size==0) return null; return removeFirst(); } /** * Retrieves and removes the last element of this list, * or returns <tt>null</tt> if this list is empty. * * @return the last element of this list, or <tt>null</tt> if * this list is empty * @since 1.6 */ public E pollLast() { if (size==0) return null; return removeLast(); } /** * Pushes an element onto the stack represented by this list. In other * words, inserts the element at the front of this list. * * <p>This method is equivalent to [email protected] #addFirst}. * * @param e the element to push * @since 1.6 */ public void push(E e) { addFirst(e); } /** * Pops an element from the stack represented by this list. In other * words, removes and returns the first element of this list. * * <p>This method is equivalent to [email protected] #removeFirst()}. * * @return the element at the front of this list (which is the top * of the stack represented by this list) * @throws NoSuchElementException if this list is empty * @since 1.6 */ public E pop() { return removeFirst(); } /** * Removes the first occurrence of the specified element in this * list (when traversing the list from head to tail). If the list * does not contain the element, it is unchanged. * * @param o element to be removed from this list, if present * @return <tt>true</tt> if the list contained the specified element * @since 1.6 */ public boolean removeFirstOccurrence(Object o) { return remove(o); } /** * Removes the last occurrence of the specified element in this * list (when traversing the list from head to tail). If the list * does not contain the element, it is unchanged. * * @param o element to be removed from this list, if present * @return <tt>true</tt> if the list contained the specified element * @since 1.6 */ public boolean removeLastOccurrence(Object o) { if (o==null) { for (Entry<E> e = header.previous; e != header; e = e.previous) { if (e.element==null) { remove(e); return true; } } } else { for (Entry<E> e = header.previous; e != header; e = e.previous) { if (o.equals(e.element)) { remove(e); return true; } } } return false; } /** * Returns a list-iterator of the elements in this list (in proper * sequence), starting at the specified position in the list. * Obeys the general contract of <tt>List.listIterator(int)</tt>.<p> * * The list-iterator is <i>fail-fast</i>: if the list is structurally * modified at any time after the Iterator is created, in any way except * through the list-iterator's own <tt>remove</tt> or <tt>add</tt> * methods, the list-iterator will throw a * <tt>ConcurrentModificationException</tt>. Thus, in the face of * concurrent modification, the iterator fails quickly and cleanly, rather * than risking arbitrary, non-deterministic behavior at an undetermined * time in the future. * * @param index index of the first element to be returned from the * list-iterator (by a call to <tt>next</tt>) * @return a ListIterator of the elements in this list (in proper * sequence), starting at the specified position in the list * @throws IndexOutOfBoundsException [email protected]} * @see List#listIterator(int) */ public ListIterator<E> listIterator(int index) { return new ListItr(index); } private class ListItr implements ListIterator<E> { private Entry<E> lastReturned = header; private Entry<E> next; private int nextIndex; private int expectedModCount = modCount; ListItr(int index) { if (index < 0 || index > size) throw new IndexOutOfBoundsException("Index: "+index+ ", Size: "+size); if (index < (size >> 1)) { next = header.next; for (nextIndex=0; nextIndex<index; nextIndex++) next = next.next; } else { next = header; for (nextIndex=size; nextIndex>index; nextIndex--) next = next.previous; } } public boolean hasNext() { return nextIndex != size; } public E next() { checkForComodification(); if (nextIndex == size) throw new NoSuchElementException(); lastReturned = next; next = next.next; nextIndex++; return lastReturned.element; } public boolean hasPrevious() { return nextIndex != 0; } public E previous() { if (nextIndex == 0) throw new NoSuchElementException(); lastReturned = next = next.previous; nextIndex--; checkForComodification(); return lastReturned.element; } public int nextIndex() { return nextIndex; } public int previousIndex() { return nextIndex-1; } public void remove() { checkForComodification(); Entry<E> lastNext = lastReturned.next; try { LinkedList.this.remove(lastReturned); } catch (NoSuchElementException e) { throw new IllegalStateException(); } if (next==lastReturned) next = lastNext; else nextIndex--; lastReturned = header; expectedModCount++; } public void set(E e) { if (lastReturned == header) throw new IllegalStateException(); checkForComodification(); lastReturned.element = e; } public void add(E e) { checkForComodification(); lastReturned = header; addBefore(e, next); nextIndex++; expectedModCount++; } final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); } } private static class Entry<E> { E element; Entry<E> next; Entry<E> previous; Entry(E element, Entry<E> next, Entry<E> previous) { this.element = element; this.next = next; this.previous = previous; } } private Entry<E> addBefore(E e, Entry<E> entry) { Entry<E> newEntry = new Entry<E>(e, entry, entry.previous); newEntry.previous.next = newEntry; newEntry.next.previous = newEntry; size++; modCount++; return newEntry; } private E remove(Entry<E> e) { if (e == header) throw new NoSuchElementException(); E result = e.element; e.previous.next = e.next; e.next.previous = e.previous; e.next = e.previous = null; e.element = null; size--; modCount++; return result; } /** * @since 1.6 */ public Iterator<E> descendingIterator() { return new DescendingIterator(); } /** Adapter to provide descending iterators via ListItr.previous */ private class DescendingIterator implements Iterator { final ListItr itr = new ListItr(size()); public boolean hasNext() { return itr.hasPrevious(); } public E next() { return itr.previous(); } public void remove() { itr.remove(); } } /** * Returns a shallow copy of this <tt>LinkedList</tt>. (The elements * themselves are not cloned.) * * @return a shallow copy of this <tt>LinkedList</tt> instance */ public Object clone() { LinkedList<E> clone = null; try { clone = (LinkedList<E>) super.clone(); } catch (CloneNotSupportedException e) { throw new InternalError(); } // Put clone into "virgin" state clone.header = new Entry<E>(null, null, null); clone.header.next = clone.header.previous = clone.header; clone.size = 0; clone.modCount = 0; // Initialize clone with our elements for (Entry<E> e = header.next; e != header; e = e.next) clone.add(e.element); return clone; } /** * Returns an array containing all of the elements in this list * in proper sequence (from first to last element). * * <p>The returned array will be "safe" in that no references to it are * maintained by this list. (In other words, this method must allocate * a new array). The caller is thus free to modify the returned array. * * <p>This method acts as bridge between array-based and collection-based * APIs. * * @return an array containing all of the elements in this list * in proper sequence */ public Object[] toArray() { Object[] result = new Object[size]; int i = 0; for (Entry<E> e = header.next; e != header; e = e.next) result[i++] = e.element; return result; } /** * Returns an array containing all of the elements in this list in * proper sequence (from first to last element); the runtime type of * the returned array is that of the specified array. If the list fits * in the specified array, it is returned therein. Otherwise, a new * array is allocated with the runtime type of the specified array and * the size of this list. * * <p>If the list fits in the specified array with room to spare (i.e., * the array has more elements than the list), the element in the array * immediately following the end of the list is set to <tt>null</tt>. * (This is useful in determining the length of the list <i>only</i> if * the caller knows that the list does not contain any null elements.) * * <p>Like the [email protected] #toArray()} method, this method acts as bridge between * array-based and collection-based APIs. Further, this method allows * precise control over the runtime type of the output array, and may, * under certain circumstances, be used to save allocation costs. * * <p>Suppose <tt>x</tt> is a list known to contain only strings. * The following code can be used to dump the list into a newly * allocated array of <tt>String</tt>: * * <pre> * String[] y = x.toArray(new String[0]);</pre> * * Note that <tt>toArray(new Object[0])</tt> is identical in function to * <tt>toArray()</tt>. * * @param a the array into which the elements of the list are to * be stored, if it is big enough; otherwise, a new array of the * same runtime type is allocated for this purpose. * @return an array containing the elements of the list * @throws ArrayStoreException if the runtime type of the specified array * is not a supertype of the runtime type of every element in * this list * @throws NullPointerException if the specified array is null */ public <T> T[] toArray(T[] a) { if (a.length < size) a = (T[])java.lang.reflect.Array.newInstance( a.getClass().getComponentType(), size); int i = 0; Object[] result = a; for (Entry<E> e = header.next; e != header; e = e.next) result[i++] = e.element; if (a.length > size) a[size] = null; return a; } private static final long serialVersionUID = 876323262645176354L; /** * Save the state of this <tt>LinkedList</tt> instance to a stream (that * is, serialize it). * * @serialData The size of the list (the number of elements it * contains) is emitted (int), followed by all of its * elements (each an Object) in the proper order. */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { // Write out any hidden serialization magic s.defaultWriteObject(); // Write out size s.writeInt(size); // Write out all elements in the proper order. for (Entry e = header.next; e != header; e = e.next) s.writeObject(e.element); } /** * Reconstitute this <tt>LinkedList</tt> instance from a stream (that is * deserialize it). */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in any hidden serialization magic s.defaultReadObject(); // Read in size int size = s.readInt(); // Initialize header header = new Entry<E>(null, null, null); header.next = header.previous = header; // Read in all elements in the proper order. for (int i=0; i<size; i++) addBefore((E)s.readObject(), header); } } |
Java LinkedList documentation:
https://docs.oracle.com/javase/7/docs/api/java/util/LinkedList.html
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