Class LinkedList
Doubly-linked list implementation of the List and Deque interfaces. Implements all optional list operations, and permits all elements (including null ).
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.
Note that this implementation is not synchronized. If multiple threads access a linked list concurrently, and at least one of the threads modifies the list structurally, it must 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 Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:
List list = Collections.synchronizedList(new LinkedList(. ));
The iterators returned by this class’s iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the Iterator’s own remove or add methods, the iterator will throw a 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.
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 ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
This class is a member of the Java Collections Framework.
Java – LinkedList poll(), pollFirst() and pollLast() methods
Example Programs for poll(), pollFirst() and pollLast() methods of LinkedList class.
LinkedList.poll()
Retrieves and removes the head (first element) of this list.
import java.util.LinkedList; class LinkedListPollMethod < public static void main(String[] args) < // Create a LinkedList of Strings LinkedListlist = new LinkedList(); // Add few Elements list.add("Element1"); list.add("Element2"); list.add("Element3"); list.add("Element4"); // Display LinkList elements System.out.println("LinkedList before: "+list); /* poll(): Retrieves and removes the head (first element) * of this list. */ System.out.println("Element removed: "+list.poll()); // Displaying list elements after poll() operation System.out.println("LinkedList after: "+list); > > LinkedList before: [Element1, Element2, Element3, Element4] Element removed: Element1 LinkedList after: [Element2, Element3, Element4]
LinkedList.pollFirst()
public E pollFirst() : Retrieves and removes the first element of this list, or returns null if this list is empty.
import java.util.LinkedList; class LinkedListPollFirstDemo < public static void main(String[] args) < // Create a LinkedList of Strings LinkedListlist = new LinkedList(); // Add few Elements list.add("Element1"); list.add("Element2"); list.add("Element3"); list.add("Element4"); // Display LinkList elements System.out.println("LinkedList before: "+list); /* pollFirst(): Retrieves and removes the first element * of this list, or returns null if this list is empty. */ System.out.println("Element removed: "+list.pollFirst()); // Display list after calling pollFirst() method System.out.println("LinkedList after: "+list); > > LinkedList before: [Element1, Element2, Element3, Element4] Element removed: Element1 LinkedList after: [Element2, Element3, Element4]
LinkedList.pollLast()
public E pollLast() : Retrieves and removes the last element of this list, or returns null if this list is empty.
import java.util.LinkedList; class LinkedListPollLastDemo < public static void main(String[] args) < // Create a LinkedList of Strings LinkedListlist = new LinkedList(); // Add few Elements list.add("Element1"); list.add("Element2"); list.add("Element3"); list.add("Element4"); // Display LinkList elements System.out.println("LinkedList before: "+list); /* pollFirst(): Retrieves and removes the first element * of this list, or returns null if this list is empty. */ System.out.println("Element removed: "+list.pollLast()); // Display after calling pollLast() method System.out.println("LinkedList after: "+list); > > LinkedList before: [Element1, Element2, Element3, Element4] Element removed: Element4 LinkedList after: [Element1, Element2, Element3]
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Comments
What’s the difference between poll() and pollFirst()? Both retrieves and remove the first list’s element and both return null if list is empty. Thanks
Giulio
poll() : This method returns the head element of the list, or null if the list is empty pollFirst(): This method works same as poll() method. remove(): It returns the head element of the LinkedList, it throws NoSuchElementException if the list is empty pollLast(): This method returns the last element of the list, it returns null if the list is empty removeFirst(): This method works same as remove() method I hope this answers your question.
Class LinkedList
Doubly-linked list implementation of the List and Deque interfaces. Implements all optional list operations, and permits all elements (including null ).
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.
Note that this implementation is not synchronized. If multiple threads access a linked list concurrently, and at least one of the threads modifies the list structurally, it must 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 Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:
List list = Collections.synchronizedList(new LinkedList(. ));
The iterators returned by this class’s iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the Iterator’s own remove or add methods, the iterator will throw a 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.
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 ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
This class is a member of the Java Collections Framework.
Java linkedlist метод poll
Doubly-linked list implementation of the List and Deque interfaces. Implements all optional list operations, and permits all elements (including null ). 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. Note that this implementation is not synchronized. If multiple threads access a linked list concurrently, and at least one of the threads modifies the list structurally, it must 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 Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:
List list = Collections.synchronizedList(new LinkedList(. ));
The iterators returned by this class’s iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the Iterator’s own remove or add methods, the iterator will throw a 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. 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 ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs. This class is a member of the Java Collections Framework.
Field Summary
Fields inherited from class java.util.AbstractList
Constructor Summary
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection’s iterator.
Method Summary
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.
Inserts all of the elements in the specified collection into this list, starting at the specified position.
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
Returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list.
Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.
Retrieves, but does not remove, the last element of this list, or returns null if this list is empty.
Removes the first occurrence of the specified element in this list (when traversing the list from head to tail).
Removes the last occurrence of the specified element in this list (when traversing the list from head to tail).
Returns an array containing all of the elements in this list in proper sequence (from first to last element).
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.