Note that code should must be in java and we are only allow to make changes in BSTChecker.java but not LabProgram.java and Node.java please make sure to write the full code of BSTChecker.java

the given code is as follow:

import java.util.$*$;

public class Node $\{$

private static String removeLeadingWhitespace$($String str$)\{$

int i $=0$;

while $($i $<mtext></mtext><mi>(</mi>$int$)$ str$.$length$())\{$

$//$ If the character at index i is not whitespace, then return the

$//$ substring that starts at i

if $(!$Character.isWhitespace$($str$.$charAt$($i$)))\{$

return str$.$substring$($i$)$;

$\}$

i$++$;

$\}$

$//$ Completing the loop means the entire string is whitespace

return new String$()$;

$\}$

public int key;

public Node left;

public Node right;

public Node$($int nodeKey, Node leftChild$)\{$

this$($nodeKey$,$ leftChild, null$)$;

$\}$

public Node$($int nodeKey$)\{$

this$($nodeKey$,$ null, null$)$;

$\}$

public Node$($int nodeKey, Node leftChild, Node rightChild$)\{$

key $=$ nodeKey;

left $=$ leftChild;

right $=$ rightChild;

$\}$

public void close$()\{$

$\}$

$//$ Counts the number of nodes in this tree

public int count$()\{$

int leftCount $=0$;

if $($left $!=$ null$)\{$

leftCount $=$ left.count$()$;

$\}$

int rightCount $=0$;

if $($right $!=$ null$)\{$

rightCount $=$ right.count$()$;

$\}$

return $1+$ leftCount $+$ rightCount;

$\}$

$//$ Inserts the new node into the tree.

public void insert$($Node node$)\{$

Node currentNode $=$ this;

while $($currentNode $!=$ null$)\{$

if $($node$.$key $$ currentNode.key$)\{$

if $($currentNode$.$left $!=$ null$)\{$

currentNode $=$ currentNode.left;

$\}$

else $\{$

currentNode.left $=$ node;

currentNode $=$ null;

$\}$

$\}$

else $\{$

if $($currentNode$.$right $!=$ null$)\{$

currentNode $=$ currentNode.right;

$\}$

else $\{$

currentNode.right $=$ node;

currentNode $=$ null;

$\}$

$\}$

$\}$

$\}$

public void insertAll$($final ArrayList keys$)\{$

for $($int key : keys$)\{$

insert$($new Node$($key$))$;

$\}$

$\}$

public static Node parse$($String treeString$)\{$

$//$ A node is enclosed in parentheses with a either just a key: $($key$),$

$//$ or a key, left child, and right child triplet: $($key$,$ left, right$).$ The

$//$ left and right children, if present, can be either a nested node or

$//$ "null".

$//$ Remove leading whitespace first

treeString $=$ Node.removeLeadingWhitespace$($treeString$)$;

$//$ The string must be non$-$empty, start with $"(",$ and end with $")"$

if $(0==$ treeString.length$()||$ treeString.charAt$(0)!=\text{'}(\text{'}$

$||$ treeString.charAt$($treeString$.$length$()-1)!=\text{'})\text{'})\{$

return null;

$\}$

$//$ Parse between parentheses

treeString $=$ treeString.substring$(1,$ treeString.length$()-1)$;

$//$ Find non$-$nested commas

ArrayList commaIndices $=$ new ArrayList$()$;

int parenCounter $=0$;

for $($int i $=0$; i $<mtext></mtext><mi>(</mi>$int$)$ treeString.length$()$; i$++)\{$

char character $=$ treeString.charAt$($i$)$;

if $(\text{'}(\text{'}==$ character$)\{$

parenCounter$++$;

$\}$

else if $(\text{'})\text{'}==$ character$)\{$

parenCounter$--$;

$\}$

else if $(\text{'},\text{'}==$ character && $0==$ parenCounter$)\{$

commaIndices.add$($i$)$;

$\}$

$\}$

$//$ If no commas, treeString is expected to be just the node's key

if $(0==$ commaIndices.size$())\{$

return new Node$($Integer$.$parseInt$($treeString$))$;

$\}$

$//$ If number of commas is not $2,$ then the string's format is invalid

if $(2!=$ commaIndices.size$())\{$

return null;

$\}$

$//$ "Split" on comma

int i$1=$ commaIndices.get$(0)$;

int i$2=$ commaIndices.get$(1)$;

String piece$1=$ treeString.substring$(0,$ i$1)$;

String piece$2=$ treeString.substring$($i$1+1,$ i$2)$;

String piece$3=$ treeString.substring$($i$2+1)$;

$//$ Make the node with just the key

Node nodeToReturn $=$ new Node$($Integer$.$parseInt$($piece$1))$;

$//$ Recursively parse children

nodeToReturn.left $=$ Node.parse$($piece$2)$;

nodeToReturn.right $=$ Node.parse$($piece$3)$;

return nodeToReturn;

$\}$

$\}$

import java.util.$*$;

public class LabProgram $\{$

public static void main$($String$[]$ args$)\{$

$//$ Get user input

Scanner reader $=$ new Scanner$($System$.$in$)$;

String userInput $=$ reader.nextLine$()$;

$//$ Parse into a binary tree

Node userRoot $=$ Node.parse$($userInput$)$;

if $($userRoot $!=$ null$)\{$

Node badNode $=$ BSTChecker.checkBSTValidity$($userRoot$)$;

if $($badNode $!=$ null$)\{$

System.out.print$($String$.$valueOf$($badNode$.$key$))$;

System.out.print$("$

$")$;

$\}$

else $\{$

System.out.print$("$No violation"$)$;

System.out.print$("$

$")$;

$\}$

$\}$

else $\{$

System.out.print$("$Failed to parse input tree"$)$;

System.out.print$("$

$")$;

$\}$

reader.close$()$;

$\}$

$\}$

Here, is the BSTChecker.java plase fill out this code

public class BSTChecker $\{$

$\}$