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  1. import java.util.*;
  2.  
  3. class node {
  4. 	int data;
  5. 	node next;
  6. 	node prev;
  7.  
  8. 	static void insert(node start, int data)
  9. 	{
  10.     	node newNode = new node();
  11.     	newNode.data = data;
  12.  
  13.     	if(start==null) {
  14.       		newNode.next=newNode.prev=null;
  15.       		start = newNode;
  16.     	} else {
  17.     		node t = start;
  18.     		while(t.next!=null)
  19.         	t = t.next;
  20.     		newNode.prev = t;
  21.     		t.next = newNode;
  22.     		newNode.next=null;
  23.     	}
  24. 	}
  25.  
  26. 	static void delete(node start, int data) {
  27.     	node t = start;
  28.     	try {
  29.     		while(t.data!=data)
  30.       			t = t.next;
  31.     	t.prev.next = t.next;
  32.     	t.next.prev = t.prev;
  33.     	} catch (NullPointerException e) {
  34. 			System.out.println("Data NOT found!");    
  35.     	}
  36. 	}
  37.  
  38. 	static void traverse(node start) {
  39.   		node t = start;
  40.     	while(t!=null) {
  41.     		System.out.println(t.data);
  42.     		t=t.next;
  43.     	}
  44. 	}
  45. }
  46.  
  47. public class Main {
  48.  
  49. 	public static void main(String[] args) {
  50.   		Scanner sc = new Scanner(System.in);
  51.  
  52. 		node start=null;
  53.  
  54.     	int ch=0;
  55.     	while(ch!=4)
  56.     	{
  57.     		System.out.println("\n1. Insert Node");
  58.     		System.out.println("2. Delete Node");
  59.     		System.out.println("3. Print nodes");
  60.     		System.out.println("4. Exit!");
  61.     		System.out.print("Enter Your Choice: ");
  62.  
  63.     		ch = sc.nextInt();
  64.  
  65.     		switch(ch)
  66.     		{
  67.       			case 1:	System.out.print("\nEnter the value of the node to insert: ");
  68.         				int val = sc.nextInt();
  69.                 	   	node.insert(start, val);
  70.                 	   	System.out.println("DEBUG	:	Start val: "+start.data);
  71.         				break;
  72.         		case 2:	System.out.print("\nEnter the value of the node you want to delete: ");
  73.         				node.delete(start, sc.nextInt());
  74.     	    			break;
  75. 	       		case 3: node.traverse(start);
  76.        					break;
  77.        			case 4:	System.out.println("\nBye!!");
  78.        					break;
  79.         		default:	System.out.println("\nWrong value: Please try again!");
  80.     		}
  81.     	}    
  82. 	} 
  83. }
Runtime error #stdin #stdout #stderr 0.07s 4386816KB
comments (?)
stdin
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1
1
1
2
1
3
3
2
2
3
4
stdout
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1. Insert Node
2. Delete Node
3. Print nodes
4. Exit!
Enter Your Choice: 
Enter the value of the node to insert:
stderr
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Exception in thread "main" java.lang.NullPointerException
	at Main.main(Main.java:70)
https://ideone.com/bgRkT6
Doubly Linked List implementation in Java failed due to lack of true pass by reference in Java.

For further reference: https://stackoverflow.com/questions/46804900/pass-by-reference-not-working-in-java

and https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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