Wednesday, September 22, 2010–Implementing a doubly linked link list in java

// Purpose: Shows a simple doubly-linked list.  Very few changes
// from singly-linked, but allows backwards traversal and
// easier insertion and deletion.
// Main builds list of words, prints it forward and backward.
// Author : Fred Swartz, 21 Feb 2006, placed in the public domain.

package linkedlistexamples;

import java.util.Scanner;

public class SimpleDoublyLinkedList {
public static void main(String[] args) {
Scanner in = new Scanner(;

Elem2 front = null; // First element of list.
Elem2 back = null; // Last element of list.

//... Read a list of words.
while (in.hasNext()) {
String word =;

Elem2 e = new Elem2(); // Create a new list element. = word; // Set the data field.

//... Two cases must be handled differently
if (front == null) {
//... When the list is empty, we have to set the front pointer.
front = e; // Back element will be set below.
} else {
//... When we already have elements, we need to link to it. = e; // Link last elem to new element.
e.prev = back;
back = e; // Update back to link to new element.

System.out.println("*** Print words in order of entry");
for (Elem2 e = front; e != null; e = {

System.out.println("*** Print words in reverse order of entry");
for (Elem2 e = back; e != null; e = e.prev) {

////////////////////////////////////////////////////////////////////////// Elem2
// Simple classes to hold data are sometimes defined with public fields.
// This practice isn't good, but was done here for simplicity.
class Elem2 {
public Elem2 next; // Link to next element in the list.
public Elem2 prev; // Link to the previous element.
public String data; // Reference to the data.

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