So, im trying to make a snake and ladders game. The way im trying to do it is by creating a board which has nodes, the first node (head) will have a node next to it, and this one will have this one as a previous node. This repeats until it gets to the total number of nodes (tha last node doesnt have a next node). The way im trying to make the snakes and ladders is by creating a relation of snakeHead and snakeTail or ladderTop and ladderBottom. I then generate a random number which will represent a specific node on the board but for some reason when i try to create the relation i get a nullPointerException on the method createSnakes, i dont get why this is happening so if someone has an idea of why it happens please tell me. Thanks in advance
public class Board {
private int numRows;
private int numColumns;
private int dimension;
private int numSnakes;
private int numLadders;
private Node head;
private Node tail;
/**
* This is the constructor
* @param numRows
* @param numColumns
*/
public Board(int numRows, int numColumns, int numSnakes, int numLadders) {
this.dimension = numColumns * numRows;
this.numLadders = numLadders;
this.numSnakes = numSnakes;
this.numRows = numRows;
this.numColumns = numColumns;
head = new Node(1);
createBoard(head, 2);
createSnakes(0);
createLadders(0);
}
/**
* This method create board
* @param prev this is the prev node
* @param i this is the counter
*/
private void createBoard(Node prev, int i){
if(i <= dimension){
if(i != dimension) {
Node current = new Node(i);
prev.setNext(current);
current.setPrev(prev);
createBoard(current, i + 1);
} else {
tail = new Node(i);
prev.setNext(tail);
tail.setPrev(prev);
}
}
}
private void createSnakes(int i){
if(i<numSnakes){
int initPosition = getInitPosition();
Node init = get(initPosition,1, head);
int endPosition = (int) (Math.random() * initPosition);
Node end = get(endPosition, 1, head);
if(init.getSnakeTail() == null && init.getSnakeHead() == null && end.getSnakeHead() == null && end.getSnakeTail() == null
&& verifyIntervals(initPosition, endPosition, 1, 0, false, false, false) == false){
init.setSnakeTail(end);
end.setSnakeHead(init);
init.setSnake((char)(i+65));
end.setSnake((char)(i+65));
createSnakes(i + 1);
} else {
createSnakes(i);
}
}
}
private void createLadders(int i){
if(i<numLadders){
int initPosition = getInitPosition();
if(initPosition==0){
createLadders(i);
}
Node init = get(initPosition,1, head);
int rank = dimension-initPosition;
int endPosition = (int) (Math.random()*rank);
if(endPosition==0 || endPosition==dimension){
createLadders(i);
}
Node end = get(endPosition+initPosition, 1, head);
if(i==numLadders){
return;
}
if(init.getSnakeTail() == null && end.getSnakeHead() == null && init.getSnakeHead() == null && end.getSnakeTail() == null
&& init.getLadderTop() == null && end.getLadderBottom() == null && init.getLadderBottom() == null && end.getLadderTop() == null
&& verifyIntervals(initPosition, endPosition, 1, 0, false, false, false) == false) {
init.setLadderTop(end);
end.setLadderBottom(init);
init.setLadder((char) (i + 48));
end.setLadder((char) (i + 48));
createLadders(i + 1);
}
else {
createLadders(i);
}
}
}
public boolean verifyIntervals(int init, int end, int varInitPos, int initPos, boolean initFound, boolean endFound,boolean inInterval){
if(inInterval==true){
return true;
}
if(varInitPos==dimension){
return false;
}
else if(varInitPos<initPos+numRows){
if(init==varInitPos){
initFound=true;
}
if(end==varInitPos){
endFound=true;
}
if(initFound==true && endFound==true){
inInterval=true;
}
return verifyIntervals(init,end,varInitPos+1,initPos,initFound,endFound,inInterval);
}
else{
return verifyIntervals(init,end,varInitPos,initPos+numRows,false,false, false);
}
}
public Node getTail() {
return tail;
}
public Node get(int position, int i, Node current){
if(i == position){
return current;
} else if(i==dimension) {
return null;
} else {
current = current.getNext();
return get(position, i+1, current);
}
}
public Node getHead() {
return head;
}
private int getInitPosition(){
return (int) (Math.random()*dimension);
}
public int getNumRows() {
return numRows;
}
public int getNumColumns() {
return numColumns;
}
public int getDimension() {
return dimension;
}
public int getNumSnakes() {
return numSnakes;
}
public int getNumLadders() {
return numLadders;
}
}
