java - iterating a linked list

Question

如果我在 java 中的链表上使用 for-each 循环，是否可以保证我会按照元素出现在列表中的顺序对元素进行迭代？

Answer 1

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.

Answer 2

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.

Answer 3

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+"->");
  }
}

Answer 4

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 = myLinkedList.listIterator();
    while( iterator.hasNext()) {
        System.out.println(iterator.next());
    }

Answer 5

每个 java.util.List 实现都需要保留顺序，因此您使用的是 ArrayList、LinkedList、Vector 等。它们中的每一个都是有序集合，并且每一个都保留插入顺序（请参阅http://download.oracle .com/javase/1.4.2/docs/api/java/util/List.html )

Answer 6

iterate LinkedList by using iterator

LinkedList<String> linkedList = new LinkedList<String>();
linkedList.add(“Mumbai”);
linkedList.add(“Delhi”);
linkedList.add(“Noida”);
linkedList.add(“Gao”);
linkedList.add(“Patna”);

Iterator<String>  itr = linkedList.iterator();
 while (itr.hasNext()) {
 System.out.println(“Element is =”+itr.next());

 }

Reference : Java Linkedlist Examples