Ytukyg

if I use a for-each loop on a linked list in java,
is it guaranteed that I will iterate on the elements in the order
in which they appear in the list?

Linked list is guaranteed to act in sequential order.

From the documentation

An ordered collection (also known as a
sequence). The user of this interface
has precise control over where in the
list each element is inserted. The
user can access elements by their
integer index (position in the list),
and search for elements in the list.

iterator()
Returns an iterator over the elements in this list in proper sequence.

I found 5 main ways to iterate over a Linked List in Java (including the Java 8 way):

1. 
   For Loop


2. 
   Enhanced For Loop


3. 
   While Loop


4. Iterator


5. Collections’s stream() util (Java8)

For loop

LinkedList<String> linkedList = new LinkedList<>();

System.out.println("==> For Loop Example.");

for (int i = 0; i < linkedList.size(); i++) {

    System.out.println(linkedList.get(i));

}

Enhanced for loop

for (String temp : linkedList) {

    System.out.println(temp);

}

While loop

int i = 0;

while (i < linkedList.size()) {

    System.out.println(linkedList.get(i));

    i++;

}

Iterator

Iterator<String> iterator = linkedList.iterator();

while (iterator.hasNext()) {

    System.out.println(iterator.next()); 

}

collection stream() util (Java 8)

linkedList.forEach((temp) -> {

    System.out.println(temp);

});

One thing should be pointed out is that the running time of For Loop or While Loop is O(n square) because get(i) operation takes O(n) time(see this for details). The other 3 ways take linear time and performs better.

As the definition of Linkedlist says, it is a sequence and you are guaranteed to get the elements in order.

eg:

import java.util.LinkedList;



public class ForEachDemonstrater {

  public static void main(String args) {

    LinkedList<Character> pl = new LinkedList<Character>();

    pl.add('j');

    pl.add('a');

    pl.add('v');

    pl.add('a');

    for (char s : pl)

      System.out.print(s+"->");

  }

}

Each java.util.List implementation is required to preserve the order so either you are using ArrayList, LinkedList, Vector, etc. each of them are ordered collections and each of them preserve the order of insertion (see http://download.oracle.com/javase/1.4.2/docs/api/java/util/List.html)

Linked list does guarantee sequential order.

Don't use linkedList.get(i), especially inside a sequential loop since it defeats the purpose of having a linked list and will be inefficient code.

Use ListIterator

    ListIterator<Object> iterator = wordTokensListJava.listIterator();

    while( iterator.hasNext()) {

        System.out.println(iterator.next());

    }