I$\text{'}$m having trouble with this. Whenever I go to test the code in the DrJava interactions pane I keep getting the error "Invalid reference name" and I don't know why. Help would be appreciated

Step $1$: Start DrJava

Start DrJava or reset the interactions pane.

Step $2$: Writing some Java code for our Linked List implementation

Enter the LLNode class into DrJava:

$/**$

$*$ The node of a linked list

$*/$

public class LLNode $\{$

$/**$ the element stored in the node $*/$

private T element;

$/**$ a reference to the next node of the list $*/$

private LLNode next;

$/**$

$*$ the constructor

$*$ @param element the element to store in the node

$*$ @param next a reference to the next node of the list

$*/$

public LLNode$($T element, LLNode next$)\{$

this.element $=$ element;

this.next $=$ next;

$\}$

$/**$

$*$ Returns the element stored in the node

$*$ @return the element stored in the node

$*/$

public T getElement$()\{$

return element;

$\}$

$/**$

$*$ Returns the next node of the list

$*$ @return the next node of the list

$*/$

public LLNode getNext$()\{$

return next;

$\}$

$/**$

$*$ Changes the node that comes after this node in the list

$*$ @param next the node that should come after this node in the list. It can be null.

$*/$

public void setNext$($LLNode next$)\{$

this.next $=$ next;

$\}$

$\}$

The rest of the code can be entered in the interactions pane. If you get an error, enter the corrected code. If you get really mixed up$,$ you can reset the interactions pane and try again.

Step $1$: Write Java commands to create the following linked list with the variable listHead pointing to the first node of the list:

$+---+---++---+---++---+---+$

listHead $--->|1|*-+---->|2|*-+---->|3|*-+--$X

$+---+---++---+---++---+---+$

Hint: You can do this with $3$ lines of code in the Interactions pane. $($For fun, try doing it with just one line!$)$ You can test it by typing listHead.getElement$(),$ listHead.getNext$().$getElement$(),$ listHead.getNext$().$getNext$().$getElement$(),$ and listHead.getNext$().$getNext$().$getNext$()$ in the Interactions pane, and if your list is correct, the outputs should be $1,2,3,$ and null.

In the above picture, each box refers to a single LLNode object, the left item in the box is the element and the right item is the next reference.

Step $2$: Try to create the same linked list, but now use a loop where, in each iteration, it creates a single LLNode instance. To create the three nodes, the loop will need to iterate three times. $($Hint: is it easier to create the list forwards or backwards?$)$

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