Node.java

import java.util.Scanner;
//Jake Swanson
//Doubly linked list example
class Node { // Node.java

  //tests node class
  public static void main(String [] args) {
    final int LIST_LENGTH = 10;
    
    //variables for test
    Node [] nodeArray = new Node[LIST_LENGTH];
        for (int i = nodeArray.length-1;i>=0;i--) nodeArray[i] = new Node((int)(Math.random() * 100), (i!=nodeArray.length-1)?nodeArray[i+1]:null);
    for (int i = 1;i<nodeArray.length;i++) nodeArray[i].setPrev(nodeArray[i-1]);
    Node head = nodeArray[0], curr = head;
    Scanner myscan = new Scanner(System.in);
    
    Node.printA(head); //see starting list
    
    //testing insert
    Node forInsert = new Node((int)(Math.random()*100));
    System.out.print("\nnew node of value " + forInsert.getItem() + "\ntell me where to insert: ");
    int pos = myscan.nextInt();
    head = Node.insertByVal(head, forInsert, pos);
    
    Node.printA(head); //see updates
    
    //testing deletion
    System.out.print("\ntell me a node value to delete: ");
    pos = myscan.nextInt();
    head = Node.deleteByVal(head, pos);
    
    Node.printA(head); //see updates
    
    Node.printR(head); //see reverse
  }

  //##### NODE CLASS ###
  //doubly linked list
  
  //getters and setters
  private int item; private Node next, prev;
  public Node(int newItem) {  this(newItem, null,null);  } // end constructor
  public Node(int newItem, Node nextNode) { this(newItem, nextNode, null); } // end constructor
  public void setItem(int newItem) { item = newItem; } // end setItem
  public int getItem( ) { return item;} // end getItem
  public void setNext(Node nextNode) { next = nextNode; } // end setNext
  public Node getNext( ) { return next; } // end getNext
  //doubly linked
  public Node(int newItem, Node nextt, Node prevv) { item = newItem; next = nextt; prev = prevv; }
  public void setPrev(Node prevv) { prev = prevv; }
  public Node getPrev() { return prev; }
  
  //Print Ahead
  public static void printA(Node head) { while (head != null) { 
    System.out.print(head.getItem() + ((head.getNext() != null)?" ":"\n")); 
    head = head.getNext(); }
  }
  
  //Print reverse.  Gets tail if not gotten.
  public static void printR(Node head) {
    System.out.print("rev: ");
    for (;head.getNext() != null; head = head.getNext()); // moves to end of list if not there
    while (head != null) { 
      System.out.print(head.getItem() + ((head.getPrev() != null)?" ":"\n")); 
      head = head.getPrev(); 
    }
  }
  
  //insert node by value
  public static Node insertByVal(Node head, Node input, int val) { //inserts node at index.  moves current node there ahead by one.
    if (head.getItem() == val) { //special case, insert at head
      input.setNext(head);
      head.setPrev(input);
      head = input;
      return head;
    }
    Node bob = head; // all other cases
    for (; bob.getNext() != null && bob.getNext().getItem() != val;bob= bob.getNext());  //puts bob at needed spot
    input.setNext(bob.getNext()); //rest of this does insertion
    if (input.getNext() != null) input.getNext().setPrev(input); //test for end of list
    bob.setNext(input);
    input.setPrev(bob);
    return head;
  }
  
  //delete a value from list
  public static Node deleteByVal(Node head, int val) {
    Node bob = head;
    if (head.getItem() == val) {
      head.getNext().setPrev(null); //special case, delete head
      return head.getNext(); //return the 2nd item as the new 'head'
    } else {
      for (; bob.getNext().getItem() != val;bob = bob.getNext()) //positions bob
        if (bob.getNext().getNext() == null ) {  //this runs if it reaches end of list
            System.out.println("item not present");
            return head;
        }
    }
    bob.setNext(bob.getNext().getNext());
    if(bob.getNext() != null) bob.getNext().setPrev(bob); //tests for null (at end of list)
    return head;
  }
} // end class Node