fork download
copy 
  1. class DoublyLinkedList<T> {
  2. 	private static class Node<T> {
  3.  
  4. 		private T element;
  5. 		private Node<T> prev; 
  6. 		private Node<T> next;
  7.  
  8. 		private Node(T element, Node<T> prev, Node<T> next) {
  9. 			this.element = element;
  10. 			this.prev = prev;
  11. 			this.next = next;
  12. 		}
  13. 	}
  14.  
  15. 	private Node<T> head;
  16. 	private Node<T> tail;
  17. 	private int listSize;
  18.  
  19. 	public DoublyLinkedList() {
  20. 		head = new Node<T>(null, null, null); 
  21. 		tail = new Node<T>(null, head, null); 
  22. 		head.next = tail;
  23. 	}
  24.  
  25. 	public void addFirst(T element) {
  26. 		addBetween(element, head, head.next); 
  27. 	}
  28.  
  29. 	public void addLast(T element) {
  30. 		addBetween(element, tail.prev, tail); 
  31. 	}
  32.  
  33. 	public void addBetween(T element, Node<T> nodeBefore, Node<T> nodeAfter) {
  34.  
  35. 		Node<T> newNode = new Node<T>(element, nodeBefore, nodeAfter); 
  36.  
  37. 		nodeBefore.next = newNode;
  38. 		nodeAfter.prev = newNode; 
  39.  
  40. 		listSize++;
  41. 	}
  42.  
  43. 	public void reverse() {
  44. 		Node<T> current = head.next; 
  45. 		Node<T> temp = null;
  46.  
  47. 		tail = head; 
  48.  
  49. 		while(current != null) { 
  50.  
  51. 			temp = current.prev; 
  52.  
  53. 			current.prev = current.next; 
  54.  
  55. 			current.next = temp; 
  56.  
  57. 			current = current.prev; 
  58. 		}
  59.  
  60. 		head = temp.prev; 
  61. 	}
  62.  
  63. 	public static void main(String[] args) {
  64.  
  65. 		DoublyLinkedList<Integer> DLL = new DoublyLinkedList<Integer>();
  66. 		DLL.addFirst(5);
  67. 		DLL.addLast(6);
  68.  
  69. 		DLL.reverse();
  70.  
  71. 		DLL.addFirst(7);
  72. 		DLL.addFirst(8);
  73. 		DLL.addFirst(9);
  74. 		DLL.addFirst(10);
  75. 		System.out.println("This works.");
  76. 		DLL.addLast(0);
  77. 		System.out.println("This doesn't.");
  78.  
  79. 	}
  80.  
  81. }
  82.  
Runtime error #stdin #stdout #stderr 0.11s 320576KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
This works.
stderr
copy 
Exception in thread "main" java.lang.NullPointerException
	at DoublyLinkedList$Node.access$102(Main.java:2)
	at DoublyLinkedList.addBetween(Main.java:37)
	at DoublyLinkedList.addLast(Main.java:30)
	at DoublyLinkedList.main(Main.java:76)
https://ideone.com/KKUtMn
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!