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Java BinaryTree balance a tree

I am trying to get a binary search tree to balance.
I balance the tree after the insert method.
I hope someone here can guide me through this.
The method is balanceTheTree(...).
I did a recursive method, I don't know if it's the best solution
public class BinaryTreeTable<E extends Comparable<E>, T> implements Table<E, T> {
private Node root;
public BinaryTreeTable() {
this.root = new Node(null, null, null);
}
#Override
public boolean insert(E key, T data) {
boolean ret;
if (this.root.key == null) {
Node toInsert = new Node(null, key, data);
this.root = toInsert;
ret = true;
} else {
Node father = this.seekFather(key);
if (father == null) {
ret = false;
} else {
Node toInsert = new Node(father, key, data);
if (key.compareTo(father.key) > 0) {
father.rSon = toInsert;
ret = true;
balanceTheTree(toInsert);
} else if (key.compareTo(father.key) < 0) {
father.lSon = toInsert;
ret = true;
balanceTheTree(toInsert);
} else {
ret = false;
}
}
}
return ret;
}
private void rightRotation(Node theN) {
Node k2 = theN.rSon;
theN.rSon = k2.lSon;
k2.lSon = theN;
}
private void leftRotation(Node theN) {
Node k1 = theN.lSon;
theN.lSon = k1.rSon;
k1.rSon = theN;
}
private void leftRightRotation(Node theN) {
leftRotation(theN.rSon);
rightRotation(theN);
}
private void rightLeftRotation(Node theN) {
rightRotation(theN.lSon);
leftRotation(theN);
}
private void balanceTheTree(Node theN) {
if (theN == null) {
} else {
if (Math.abs(Math.subtractExact(computeH(theN.rSon), computeH(theN.lSon))) > 1) {
System.out.println("A droite " + theN.getLabel());
if (computeH(theN.lSon) > computeH(theN.rSon)) {
leftRotation(theN);
} else {
leftRightRotation(theN);
}
} else if (Math.abs(Math.subtractExact(computeH(theN.lSon), computeH(theN.rSon))) > 1) {
System.out.println("A gauche");
} else {
balanceTheTree(theN.rSon);
balanceTheTree(theN.lSon);
}
}
}
private int computeH(Node theN) {
int ret = 1;
if (theN == null) {
ret = 0;
} else if ((theN.lSon != null) && (theN.rSon == null)) {
ret = computeH(theN.lSon) + 1;
} else if ((theN.lSon == null) && (theN.rSon != null)) {
ret = computeH(theN.rSon) + 1;
} else if ((theN.lSon != null) && (theN.rSon != null)) {
ret = Math.max(computeH(theN.lSon), computeH(theN.rSon)) + 1;
}
return ret;
}
public class Node {
// Attributs
private Node lSon ;
private Node rSon ;
private Node father ;
private T theValue ;
private E key ;
// Constructeur
public Node (Node father, E key, T theValue) {
this.father = father;
this.key = key;
this.theValue = theValue;
}
public String getLabel() {
return String.valueOf(key);
}
public Node getLeft() {
return lSon;
}
public Node getRight() {
return rSon;
}
public Node clone() {
return new Node(this.father, this.key, this.theValue);
}
}
}
The computeH() method allows me to know the size of a node
The insertion method works correctly.
The tree i want to balance
public static void main(String[] args) {
BinaryTreeTable binaryTreeTable = new BinaryTreeTable();
binaryTreeTable.insert(10, "Test");
binaryTreeTable.insert(5, "Test");
binaryTreeTable.insert(7, "Test");
binaryTreeTable.insert(3, "Test");
binaryTreeTable.insert(4, "Test");
binaryTreeTable.insert(15, "Test");
binaryTreeTable.insert(19, "Test");
binaryTreeTable.insert(16, "Test");
binaryTreeTable.insert(20, "Test");
binaryTreeTable.showTree();
}

Java Maze Solver - Stack does not pop when pop() is called

I'm working on an assignment where I have to solve a maze through backtracking (using a stack!) and the logic of the code is basically done, but the main problem is whenever I call pop() on my stack, it does not pop.So for now I have manually added (hardcoded) the parts in the maze where it is supposed to pop(). I am using my own stack that is using Linked Nodes and have ran JUnit and Main tests and it does indeed work (doubting myself here now). I have also used the Java stack and I get the same result.
Here is my code logic: As you can see in the method mazeSolver, at the bottom, I have a few if statements that check if i (operations performed) is at a certain point and it will "backtrack", but I am manually setting the position. The very last else statement is the part where I pop(). Any help would very much be appreciated.
public class MazeSolver {
private char[][] printMaze;
private char[][] solveMaze;
public MazeSolver() {
super();
}
private class Position {
private int x;
private int y;
Position(int y, int x) {
this.x = x;
this.y = y;
}
public int getX() {
return this.x;
}
public int getY() {
return this.y;
}
public void setX(int x) {
this.x = x;
}
public void setY(int y) {
this.y = y;
}
}
public boolean solve(boolean printUpdates) {
char space = ' ';
Stack<Position> stack = new Stack<Position>();
//Stack stack = new Stack();
Position cp = new Position(1, 0);
boolean done = true;
char c = 'C';
char x = 'X';
int i = 0;
while (done) {
// check right
if (printMaze[cp.getY()][cp.getX() + 1] == space && printMaze[cp.getY()][cp.getX() + 1] != x) {
cp.setX(cp.getX() + 1);
stack.push(cp);
printMaze[cp.getY()][cp.getX()] = 'C';
}
// check bottom
else if (printMaze[cp.getY() + 1][cp.getX()] == space && printMaze[cp.getY() + 1][cp.getX()] != x
&& printMaze[cp.getY() + 1][cp.getX()] != x) {
cp.setY(cp.getY() + 1);
stack.push(cp);
printMaze[cp.getY()][cp.getX()] = 'C';
}
// check top
else if (printMaze[cp.getY() - 1][cp.getX()] == space && printMaze[cp.getY() - 1][cp.getX()] != x) {
cp.setY(cp.getY() - 1);
stack.push(cp);
printMaze[cp.getY()][cp.getX()] = 'C';
}
// check left
else if (printMaze[cp.getY()][cp.getX() - 1] == space && printMaze[cp.getY()][cp.getX() - 1] != x) {
cp.setX(cp.getX() - 1);
stack.push(cp);
printMaze[cp.getY()][cp.getX()] = 'C';
}
//else {
/*
if (i == 6) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(1);
cp.setX(5);
} else if (i == 27) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(1);
cp.setX(20);
}
else if (i == 37) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(2);
cp.setX(18);
}
else if (i == 68) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(13);
cp.setX(22);
} else if (i == 69) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(14);
cp.setX(22);
}
else if (i == 70) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(15);
cp.setX(22);
} else if (i == 71) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(16);
cp.setX(22);
} else if (i == 72) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(17);
cp.setX(22);
} else if (i == 103) {
printMaze[cp.getY()][cp.getX()] = 'X';
cp.setY(21);
cp.setX(31);
} */else {
printMaze[cp.getY()][cp.getX()] = 'X';
stack.pop();
cp.setY(((Position) stack.top()).getY());
cp.setX(((Position) stack.top()).getX());
}
//}
i++;
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
// System.out.println(stack.top().getX() + ", " + stack.top().getY());
System.out.println(cp.getY() + ", " + cp.getX() + " i = " + i);
printMaze();
}
System.out.println("success");
return false;
}
public void printMaze() {
for (int i = 0; i < printMaze.length; i++) {
for (int j = 0; j < printMaze[i].length; j++) {
System.out.print(printMaze[i][j]);
}
System.out.println("");
}
}
public boolean loadMaze(String filename) {
BufferedReader br = null;
FileReader fr = null;
ArrayList<String> lines = new ArrayList<String>();
try {
fr = new FileReader(filename);
br = new BufferedReader(fr);
String line;
br = new BufferedReader(new FileReader(filename));
while ((line = br.readLine()) != null) {
lines.add(line);
}
printMaze = new char[lines.size()][];
solveMaze = new char[lines.size()][];
for (int i = 0; i < lines.size(); i++) {
printMaze[i] = new char[lines.get(i).length()];
solveMaze[i] = new char[lines.get(i).length()];
for (int j = 0; j < lines.get(i).length(); j++) {
solveMaze[i][j] = lines.get(i).charAt(j);
printMaze[i][j] = lines.get(i).charAt(j);
if (solveMaze[i][j] == 'S') {
// hint you need to do this but you do not have the
// instance variable yet
// start = new Position(i, j);
}
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null)
br.close();
if (fr != null)
fr.close();
} catch (IOException ex) {
return false;
}
}
return true;
}
Here is my stack implementation if interested.
public class Stack<Item> implements StackInterface<Item> {
private int size;
private class Link {
private Item data;
public Link next;
public Link(Item data, Link next) {
this.data = data;
this.next = next;
}
public Item getData() {
return data;
}
}
private Link topStackLink = null;
public Stack() {
this.size = 0;
}
#Override
public void push(Item item) {
if (topStackLink == null) {
topStackLink = new Link(item, null);
} else {
topStackLink = new Link(item, topStackLink);
}
this.size++;
}
#Override
public void pop() {
// TODO Auto-generated method stub
if (topStackLink != null) {
topStackLink = topStackLink.next;
this.size--;
} else {
throw new java.util.EmptyStackException();
}
}
#Override
public Item top() {
if (topStackLink != null) {
return topStackLink.data;
} else {
throw new java.util.EmptyStackException();
}
}
#Override
public Item topAndPop() {
// TODO Auto-generated method stub
if (topStackLink != null) {
Item item = topStackLink.data;
pop();
return item;
} else {
throw new java.util.EmptyStackException();
}
}
#Override
public boolean isEmpty() {
if (topStackLink == null) {
return true;
} else {
return false;
}
}
#Override
public void makeEmpty() {
// TODO Auto-generated method stub
topStackLink = null;
this.size = 0;
}
#Override
public int size() {
return this.size;
}

NullPointerException - LinkedList [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
Okey, I have no idea why I am getting this NullPointException. I have been trying for hours now, I AM GOING CRAZY!
Maybe some of u guys can help me. If u need more information, I will try to give it, just ask 4 it.
This is a link to a picture - CLICK ME! - NullPointerException
public class KjedetMengde<T> implements MengdeADT<T> {
private static Random rand = new Random();
private int antall; // antall elementer i mengden
private LinearNode<T> start;
/**
* Oppretter en tom mengde.
*/
public KjedetMengde() {
antall = 0;
start = null;
}//
#Override
public void leggTil(T element) {
if (!(inneholder(element))) {
LinearNode<T> node = new LinearNode<T>(element);
node.setNeste(start);
start = node;
antall++;
}
}
public void leggTilAlle(MengdeADT<T> m2) {
Iterator<T> teller = m2.oppramser();
while (teller.hasNext()) {
leggTil(teller.next());
}
}
#Override
public T fjernTilfeldig() {
LinearNode<T> forgjenger, aktuell;
T resultat = null;
if (!erTom()) {
int valg = rand.nextInt(antall) + 1;
if (valg == 1) {
resultat = start.getElement();
start = start.getNeste();
} else {
forgjenger = start;
for (int nr = 2; nr < valg; nr++) {
forgjenger = forgjenger.getNeste();
}
aktuell = forgjenger.getNeste();
resultat = aktuell.getElement();
forgjenger.setNeste(aktuell.getNeste());
}
antall--;
} // if
return resultat;
}//
#Override
public T fjern(T element) {
boolean funnet = false;
LinearNode<T> forgjenger = null;
LinearNode<T> aktuell = null;
T resultat = null;
if (!erTom()) {
if (start.getElement().equals(element)) {
resultat = start.getElement();
start = start.getNeste();
antall--;
} else {
forgjenger = start;
aktuell = start.getNeste();
for (int i = 1; i < antall && !funnet; i++) {
if (aktuell.getElement().equals(element)) {
funnet = true;
} else {
forgjenger = aktuell;
aktuell = aktuell.getNeste();
}
}
}
if (funnet) {
resultat = aktuell.getElement();
forgjenger.setNeste(aktuell.getNeste());
antall--;
}
}
return resultat;
}//
#Override
public MengdeADT<T> union(MengdeADT<T> m2) {// OBS! En bedre i kladdeopg4
KjedetMengde<T> begge = new KjedetMengde<T>();
LinearNode<T> aktuell = start;
while (aktuell != null) {
begge.leggTil(aktuell.getElement());
aktuell = aktuell.getNeste();
} // while
Iterator<T> teller = m2.oppramser();
while (teller.hasNext()) {
begge.leggTil(teller.next());
}
return begge;
}//
private void settInn(T element) {
LinearNode<T> nyNode = new LinearNode<T>(element);
nyNode.setNeste(start);
start = nyNode;
antall++;
}
#Override
public boolean inneholder(T element) {
boolean funnet = false;
LinearNode<T> aktuell = start;
for (int søk = 0; søk < antall && !funnet; søk++) {
if (aktuell.getElement().equals(element)) {
funnet = true;
} else {
aktuell = aktuell.getNeste();
}
}
return funnet;
}
#Override
public boolean erLik(MengdeADT<T> m2) {
boolean likeMengder = true;
T element = null;
if (antall() == m2.antall()) {
Iterator<T> teller = m2.oppramser();
while (teller.hasNext() && likeMengder) {
element = teller.next();
if (!this.inneholder(element)) {
likeMengder = false;
}
}
}
return likeMengder;
}
#Override
public boolean erTom() {
return antall == 0;
}
#Override
public int antall() {
return antall;
}
#Override
public Iterator<T> oppramser() {
return new KjedetIterator<T>(start);
}
#Override
public MengdeADT<T> snitt(MengdeADT<T> m2) {
KjedetMengde<T> kjede = new KjedetMengde<T>();
KjedetMengde<T> snitt = new KjedetMengde<T>();
LinearNode<T> aktuell = start;
while (aktuell != null) {
kjede.leggTil(aktuell.getElement());
aktuell = aktuell.getNeste();
}
Iterator<T> teller = m2.oppramser();
while (teller.hasNext()) {
T element = teller.next();
if (kjede.inneholder(element)) {
snitt.leggTil(element);
}
}
return snitt;
}
#Override
public MengdeADT<T> differans(MengdeADT<T> m2) { // (m1- m2)
KjedetMengde<T> kjede = new KjedetMengde<T>();
LinearNode<T> aktuell = start;
while (aktuell != null) {
kjede.leggTil(aktuell.getElement());
aktuell = aktuell.getNeste();
}
Iterator<T> teller = m2.oppramser();
while (teller.hasNext()) {
T element = teller.next();
if (kjede.inneholder(element)) {
kjede.fjern(element);
}
}
return kjede;
}
public String toString() {
String resultat = " ";
LinearNode<T> aktuell = start;
while (aktuell != null) {
resultat += aktuell.getElement().toString() + "\t";
aktuell = aktuell.getNeste();
}
return resultat;
}
}// class
public class Hobby {
private String hobbyNavn;
public Hobby (String hobby) {
hobbyNavn = hobby;
}
public String toString() {
return ("< " + hobbyNavn + " >");
}
public boolean equals (Object hobby2) {
Hobby hobbyDenAndre = (Hobby) hobby2;
return(hobbyNavn.equals(hobbyDenAndre.getHobbyNavn()));
}
public String getHobbyNavn() {
return hobbyNavn;
}
} //class

You are not initialising your hobbyer variable. You are even setting it to null in the constructor of Medlem.
Try
hobbyer = new KjedetMengde<Hobby>();
in either line 8 or 13 in your Medlem class.

Why will my program not go into my while loop?

I'm working on a program that will take a name and number of a periodic element, store it in a tree and then print it out in different orders.
When I try and run my main class it asks for the name, but then it doesn't go into the while loop.
Here is my main class.
public class BinarySearchTree
{
public static void main(String[] args)
{
Scanner conIn = new Scanner(System.in);
String name;
int atomicNum;
BSTInterface<PeriodicElement> elements = new BSTree<PeriodicElement>();
PeriodicElement element;
int numElements;
String skip;
System.out.print("Element name (press Enter to end): ");
name = conIn.nextLine();
while (!name.equals(""));
{
System.out.print("Atomic Number: ");
atomicNum = conIn.nextInt();
skip = conIn.nextLine();
element = new PeriodicElement(name, atomicNum);
elements.add(element);
System.out.print("Element name (press ENTER TO END): ");
name = conIn.nextLine();
}
System.out.println();
System.out.println("Periodic Elements");
numElements = elements.reset(BSTree.INORDER);
for (int count = 1; count <= numElements; count++)
{
System.out.println(elements.getNext(BSTree.INORDER));
}
}
}
Here is my Binary Search Tree
public class BSTree <T extends Comparable<T>>
implements BSTInterface<T>
{
protected BSTNode<T> root;
boolean found;
protected LinkedUnbndQueue<T> inOrderQueue;
protected LinkedUnbndQueue<T> preOrderQueue;
protected LinkedUnbndQueue<T> postOrderQueue;
public BSTree()
{
root = null;
}
public boolean isEmpty()
{
return (root == null);
}
private int recSize(BSTNode<T> tree)
{
if(tree == null)
{
return 0;
}
else
{
return recSize(tree.getLeft()) + recSize(tree.getRight()) + 1;
}
}
public int size()
{
int count = 0;
{
if(root != null)
{
LinkedStack<BSTNode<T>> hold = new LinkedStack<BSTNode<T>>();
BSTNode<T> currNode;
hold.push(root);
while(!hold.isEmpty())
{
currNode = hold.top();
hold.pop();
count++;
if(currNode.getLeft() != null)
{
hold.push(currNode.getLeft());
}
if(currNode.getRight() != null)
{
hold.push(currNode.getRight());
}
}
}
//System.out.println(count);
return count;
}
}
public boolean recContains(T element, BSTNode<T> tree)
{
if(tree == null)
{
return false;
}
else if(element.compareTo(tree.getInfo()) < 0)
{
return recContains(element, tree.getLeft());
}
else if(element.compareTo(tree.getInfo()) > 0)
{
return recContains(element, tree.getRight());
}
else
{
return true;
}
}
public boolean contains (T element)
{
//System.out.println("Tree contains: " + recContains(element, root));
return recContains(element, root);
}
public T recGet(T element, BSTNode<T> tree)
{
if(tree == null)
{
return null;
}
else if(element.compareTo(tree.getInfo()) < 0)
{
return recGet(element, tree.getLeft());
}
else if(element.compareTo(tree.getInfo()) > 0)
{
return recGet(element, tree.getRight());
}
else
{
return tree.getInfo();
}
}
public T get(T element)
{
//System.out.println(recGet(element, root));
return recGet(element, root);
}
public void add(T element)
{
root = recAdd(element, root);
}
private BSTNode<T> recAdd(T element, BSTNode<T> tree)
{
if(tree == null)
{
tree = new BSTNode<T>(element);
}
else if(element.compareTo(tree.getInfo()) <= 0)
{
tree.setLeft(recAdd(element, tree.getLeft()));
}
else
{
tree.setRight(recAdd(element, tree.getRight()));
}
return tree;
}
public boolean remove(T element)
{
root = recRemove(element, root);
return found;
}
private BSTNode<T> recRemove(T element, BSTNode<T> tree)
{
if(tree == null)
{
found = false;
}
else if (element.compareTo(tree.getInfo()) < 0)
{
tree.setLeft(recRemove(element, tree.getLeft()));
}
else if (element.compareTo(tree.getInfo()) > 0)
{
tree.setRight(recRemove(element, tree.getRight()));
}
else
{
tree = removeNode(tree);
found = true;
}
return tree;
}
private BSTNode<T> removeNode(BSTNode<T> tree)
{
T data;
if(tree.getLeft() == null)
{
return tree.getRight();
}
else if(tree.getRight() == null)
{
return tree.getLeft();
}
else
{
data = getPredecessor(tree.getLeft());
tree.setInfo(data);
tree.setLeft(recRemove(data, tree.getLeft()));
return tree;
}
}
private T getPredecessor(BSTNode<T> tree)
{
while (tree.getRight() != null)
{
tree = tree.getRight();
}
return tree.getInfo();
}
public int reset(int orderType)
{
int numNodes = size();
if(orderType == INORDER)
{
inOrderQueue = new LinkedUnbndQueue<T>(numNodes);
}
else
{
if(orderType == PREORDER)
{
preOrderQueue = new LinkedUnbndQueue<T>(numNodes);
preOrder(root);
}
if(orderType == POSTORDER)
{
postOrderQueue = new LinkedUnbndQueue<T>(numNodes);
postOrder(root);
}
}
return numNodes;
}
public T getNext(int orderType)
{
if(orderType == INORDER)
{
return inOrderQueue.dequeue();
}
else
{
if(orderType == PREORDER)
{
return preOrderQueue.dequeue();
}
else
{
if(orderType == POSTORDER)
{
return postOrderQueue.dequeue();
}
else
{
return null;
}
}
}
}
private void inOrder(BSTNode<T> tree)
{
if(tree != null)
{
inOrder(tree.getLeft());
inOrderQueue.enqueue(tree.getInfo());
inOrder(tree.getRight());
}
}
private void preOrder(BSTNode<T> tree)
{
if(tree != null)
{
preOrderQueue.enqueue(tree.getInfo());
preOrder(tree.getLeft());
preOrder(tree.getRight());
}
}
private void postOrder(BSTNode<T> tree)
{
if(tree != null)
{
postOrder(tree.getLeft());
postOrder(tree.getRight());
postOrderQueue.enqueue(tree.getInfo());
}
}
}
Here is the Binary Search Tree Node class
public class BSTNode <T extends Comparable<T>>
{
protected T info;
protected BSTNode<T> left;
protected BSTNode<T> right;
public BSTNode(T info)
{
this.info = info;
left = null;
right = null;
}
public void setInfo(T info)
{
this.info = info;
}
public T getInfo()
{
return info;
}
public void setLeft(BSTNode<T> link)
{
left = link;
}
public void setRight(BSTNode<T> link)
{
right = link;
}
public BSTNode<T> getLeft()
{
return left;
}
public BSTNode<T> getRight()
{
return right;
}
}

Remove the semi-colon that is terminating the while statement
while (!name.equals(""));
^

Remove the semi colon after the while statment because a semi colon makes it end there while a { is the start if while something is true or not (!) and it should end as you obviously know with a }.

GXT Paging Grid service method

In GXT is an example:
http://www.sencha.com/examples/#ExamplePlace:paginggrid
Where I can see realization of this method:
service.getPosts(loadConfig, callback);
or any other similar service

For example, here -
http://spring-rapid.googlecode.com/svn/trunk/atom-explorer/src/main/java/com/atom/ebank/wfront/examples/resources/server/ExampleServiceImpl.java
...
#Override
public PagingLoadResult<Post> getPosts(PagingLoadConfig config) {
if (posts == null) {
loadPosts();
}
if (config.getSortInfo().size() > 0) {
SortInfo sort = config.getSortInfo().get(0);
if (sort.getSortField() != null) {
final String sortField = sort.getSortField();
if (sortField != null) {
Collections.sort(posts, sort.getSortDir().comparator(new Comparator<Post>() {
public int compare(Post p1, Post p2) {
if (sortField.equals("forum")) {
return p1.getForum().compareTo(p2.getForum());
} else if (sortField.equals("username")) {
return p1.getUsername().compareTo(p2.getUsername());
} else if (sortField.equals("subject")) {
return p1.getSubject().compareTo(p2.getSubject());
} else if (sortField.equals("date")) {
return p1.getDate().compareTo(p2.getDate());
}
return 0;
}
}));
}
}
}
ArrayList<Post> sublist = new ArrayList<Post>();
int start = config.getOffset();
int limit = posts.size();
if (config.getLimit() > 0) {
limit = Math.min(start + config.getLimit(), limit);
}
for (int i = config.getOffset(); i < limit; i++) {
sublist.add(posts.get(i));
}
return new PagingLoadResultBean<Post>(sublist, posts.size(), config.getOffset());
}
...