Insert nodes into a linked list

Question

I am new to java, so sorry in advance if this is horrible. Basically, I believe that you need to insert a number, say, a linked list [10 30 50 70] I want to insert 40, so I type in the next, and then again, and now I'm at 50. I want to insert earlier, but when I I type up to, and then 40 it just returns [10 30 50 70] total = 4, and the current is 50.

public void insertAfter(long dd)  {   
    Node newNode = new Node(dd);   // insert a new node after current node; 
    newNode = current;
    current = previous;
    if (current != null) {     // if current is not null, don't change it; otherwise set current to new node.
       return;

    } 
    else {
     newNode = current;
    }
}

public void insertBefore(long dd) {   
    Node newNode = new Node(dd);  // insert a new node before current node, always set current to the new node
    current = previous; // to be implemented
    newNode = current;
}

Here is the code that calls these two methods and provides a list. Any suggestions?

package hw4;

import java.io.*;                 // for I/O

class TestLinkList {

   public static void main(String[] args) throws IOException
      {
      LinkList theList = new LinkList();          // new list

      theList.insertFirst(70);
      theList.insertFirst(50);
      theList.insertFirst(30);
      theList.insertFirst(10);
      theList.reset();

      while(true) {
         System.out.print("Enter first letter of reset, ");
         System.out.print("next, get, before, after, delete, exit: ");
         System.out.flush();
         int choice = getChar();         // get user option
         long value;
         switch(choice)
            { 
            case 'r':                    // reset (to first)
               theList.reset();
               theList.displayList();
               break;
            case 'e':                    // exit the while loop
                break;
            case 'n':                    // advance to next item
               if( theList.getCurrent() != null ) {
                  theList.nextLink();
                  theList.displayList();
               } else
                  System.out.println("Can't go to next link");
               break;
            case 'g':                    // get current item
               if( theList.getCurrent() != null ) {
                  value = theList.getCurrent().dData;
                  System.out.println("Returned " + value);
                  }
               else
                  System.out.println("List is empty");
               break;
            case 'b':                    // insert before current
               System.out.print("Enter value to insert: ");
               System.out.flush();
               value = getInt();
               theList.insertBefore(value);
               theList.displayList();
               break;
            case 'a':                    // insert after current
               System.out.print("Enter value to insert: ");
               System.out.flush();
               value = getInt();
               theList.insertAfter(value);
               theList.displayList();
               break;
            case 'd':                    // delete current item
               if( theList.getCurrent() != null ) {
                  value = theList.deleteCurrent();
                  System.out.println("Deleted " + value);
                  theList.displayList();
               } else
                  System.out.println("Can't delete");
               break;
            default:
               System.out.println("Invalid entry");
            }  // end switch

            if (choice == 'e') break;
         }  // end while

   }  // end main()

   public static String getString() throws IOException {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      String s = br.readLine();
      return s;
   }

   public static char getChar() throws IOException {
      String s = getString();
      return s.charAt(0);
   }

   public static int getInt() throws IOException {
      String s = getString();
      return Integer.parseInt(s);
   }

}  

Answer 1

Since this is homework, I will take you in the right direction.

Your method is insertAfterincorrect.

In the first line, you create newnode. In the second line, you overwrite this newnode with the current.

Start with these mistakes.

- . , , node .