Java LinkedList
In the previous chapter, you learned about the ArrayList class. The LinkedList class is almost identical to the ArrayList :
Example
// Import the LinkedList class import java.util.LinkedList; public class Main < public static void main(String[] args) < LinkedListcars = new LinkedList(); cars.add("Volvo"); cars.add("BMW"); cars.add("Ford"); cars.add("Mazda"); System.out.println(cars); > > ArrayList vs. LinkedList
The LinkedList class is a collection which can contain many objects of the same type, just like the ArrayList .
The LinkedList class has all of the same methods as the ArrayList class because they both implement the List interface. This means that you can add items, change items, remove items and clear the list in the same way.
However, while the ArrayList class and the LinkedList class can be used in the same way, they are built very differently.
How the ArrayList works
The ArrayList class has a regular array inside it. When an element is added, it is placed into the array. If the array is not big enough, a new, larger array is created to replace the old one and the old one is removed.
How the LinkedList works
The LinkedList stores its items in «containers.» The list has a link to the first container and each container has a link to the next container in the list. To add an element to the list, the element is placed into a new container and that container is linked to one of the other containers in the list.
When To Use
Use an ArrayList for storing and accessing data, and LinkedList to manipulate data.
LinkedList Methods
For many cases, the ArrayList is more efficient as it is common to need access to random items in the list, but the LinkedList provides several methods to do certain operations more efficiently:
| Method | Description | Try it |
|---|---|---|
| addFirst() | Adds an item to the beginning of the list. | Try it » |
| addLast() | Add an item to the end of the list | Try it » |
| removeFirst() | Remove an item from the beginning of the list. | Try it » |
| removeLast() | Remove an item from the end of the list | Try it » |
| getFirst() | Get the item at the beginning of the list | Try it » |
| getLast() | Get the item at the end of the list | Try it » |
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.
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.
What is linked list class for in java
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.