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How to make two Threads wait and notify the correct way in Tic Tac Toe game

I followed some discussion on the website and implemented some suggestions but I was not able to complete the task.
I have this assignment to build Tic Tac Toe game in Java.
There's a lot of tutorials on the web I know, but I wanted to build it using threads for each player so that only one player at a time could enter X/O to the board and I was not able to figure out the implementation for the wait/ notify.
To be honest, I find it a bit confusing! I guess the logic is 90% done, and I am wondering how to finish it.
Basically, I have these classes:
abstract public class Player extends Thread
public class HumanPlayer extends Player
public class MachinePlayer extends Player
public class Board
public class Game
public class Main
I'll paste first the players classes. Notice the run method I tried to Synchronize on top of the gameOver variable:
Player.java
abstract public class Player extends Thread {
abstract int getMyTurn() ;
abstract String getPlayerName() ;
abstract void setPlayerName(String n ) ;
abstract void setSign(int n ) ;
abstract int getSign() ;
}
MachinePlayer.java
import java.util.Random;
public class MachinePlayer extends Player {
private String name ;
private int sign ;
Board board ;
public MachinePlayer(Board board) {
this.board = board;
}
#Override
public void run() {
System.out.println("Player "+name+" turn:" );
while (!board.isGameOver())
{
board.setCurrentPlayerTurn(this.getSign()); // i think it keeps track of which player is holding the lock ?
Move move = generateRandomMove();
board.makeMove(this, move.getX(), move.getY() );
}
}
#Override
int getMyTurn() {
return 0;
}
#Override
public String getPlayerName() {
return name;
}
#Override
public void setPlayerName(String name) {
this.name = name;
}
#Override
void setSign(int sign) {
this.sign = sign ;
}
#Override
int getSign() {
return sign;
}
private Move generateRandomMove(){
while (true)
{
int x = getRandomNumber(0,board.getBoardSize()) ;
int y = getRandomNumber(0,board.getBoardSize()) ;
if (board.isPositionAvalabile(x, y ))
{
return new Move(x,y);
}
}
// todo implement the best move !
}
public int getRandomNumber(int min, int max) {
return (int) ((Math.random() * (max - min)) + min);
}
}
HumanPlayer.java
public class HumanPlayer extends Player {
private String name ;
private int sign ;
private Board board ;
public HumanPlayer(Board board) {
this.board = board;
}
#Override
public void run() {
while (!board.isGameOver())
{
board.setCurrentPlayerTurn(this.getSign()); // I think it keeps track of which player is holding the lock ?
Move move = requestMoveFormHuman(); // request move for human player // will be changed in the GUI?
board.makeMove(this, move.getX() , move.getY()); // check for move logic here >
}
}
#Override
int getSign() {
return sign;
}
#Override
int getMyTurn() {
return 0;
}
#Override
public String getPlayerName() {
return name;
}
#Override
public void setPlayerName(String name) {
this.name = name;
}
#Override
void setSign(int n) {
this.sign = n ;
}
// logic
private Move requestMoveFormHuman(){
int i=0 ;
while (true)
{
System.out.println(i);
Move move = requestMove() ;
int x = move.getX();
int y = move.getY();
if (board.isPositionAvalabile(x,y))
{
return new Move(x,y);
}
}
}
private Move requestMove() {
System.out.println("Player "+name+" turn:" );
System.out.println("Enter Row number: ");
int x = ScanInt();
System.out.println("Enter Coulmn number ");
int y = ScanInt();
return new Move(x ,y ) ;
}
private int ScanInt(){
Scanner scan = new Scanner(System.in);
// This method reads the number provided using keyboard
int num = scan.nextInt();
// Closing Scanner after the use
return num;
}
}
Main.java
public class Main {
public static void main(String[] args) {
Game game = new Game() ;
game.start();
}
}
Board.java
import java.util.HashMap;
import java.util.Scanner;
public class Board {
private int currentPlayerTurn = 0 ;
public int getBoardSize() {
return boardSize;
}
private int boardSize ;
private int[][] board_values ;
private boolean gameOver ;
private HashMap<String , String> result_history;
public Board(int boardSize) {
this.boardSize = boardSize;
board_values = new int[boardSize][boardSize];
for (int i = 0; i < boardSize; i++) {
for (int j = 0 ; j < boardSize; j++)
board_values[i][j] = 0 ;
}
System.out.println("");
}
private String getSign(int n) {
if (n==1)
return "X" ;
if (n==2)
return "0" ;
return " " ; // empty cell
}
public void printBoard(){
// todo change to ui components
for (int i = 0 ; i < boardSize ; i++)
{
for (int j = 0 ; j < boardSize ; j++)
{
System.out.print("|");
System.out.print(" " + getSign(board_values[i][j])+ " ");
System.out.print("|");
}
System.out.println("");
System.out.println("----------------------------------" );
}
}
/** is this the Synchronized one ? */
public boolean makeMove(Player player , int x , int y ) {
/*Update Board Value
insert 1 in the 2d board at x,y for player 1
insert 2 in the 2d board at x,y for player 2
*/
int sign = player.getSign();
updateBoard(x,y , sign ) ;
/*print Board*/
printBoard();
/* check for winner */
doWeHaveAwinner(x,y , sign);
return true ;
}
/*check the whole row (x) for if all signs are equals
, checks the whole column (x) for if all signs are equals
check diagonal if x=y */
private boolean doWeHaveAwinner(int x, int y, int sign) {
// TODO: 16/01/2022
return false ;
}
private void updateBoard(int x, int y , int sign ) {
board_values[x][y] = sign ;
}
public boolean isPositionAvalabile(int x , int y ){
return !(x>this.boardSize || x < 0 || y>this.boardSize || y < 0) ;
}
private void checkMove() {
// todo > ?
}
private void resetBoard(){
// todo set al values to 0
}
private void updateResultHistory(){
// TODO: 16/01/2022 update <Winner Name , Ps+1 >
}
private int ScanInt(){
Scanner scan = new Scanner(System.in);
System.out.print("Enter any number: ");
// This method reads the number provided using keyboard
int num = scan.nextInt();
// Closing Scanner after the use
return num;
}
/*Get Set*/
public synchronized boolean isGameOver() {
return gameOver;
}
public void setGameOver(boolean gameOver) {
this.gameOver = gameOver;
}
public int getCurrentPlayerTurn() {
return currentPlayerTurn;
}
public void setCurrentPlayerTurn(int currentPlayerTurn) {
this.currentPlayerTurn = currentPlayerTurn;
}
}
And here is Game.java, it basically inits 2 players.
Notice that in each player init I passed the board instance as a parameter.
It might a look little bit messy but I think passing the board instance for the players is the important thing here. Also I called the player1().start and player2.start()
Game.java
public class Game {
private Player player1 ;
private Player player2 ;
private Board board ;
private void initBoard(){
/* request board size */
int board_size = requestBoardSize();
board = new Board(board_size); // Synchronized class fields ?
}
private void initGameMode(){
/*
init the players objects as follows
1 - for human-machine game
2 - for machine-human game, and
3 - for human-human game
*/
System.out.println(Utils.str_gameType);
Scanner scanner = new Scanner( System.in);
int game_mode = scanner.nextInt( );
switch (game_mode) {
case 1:
/* init game type1 human-machine Game*/
player1 = new HumanPlayer(board);
player2 = new MachinePlayer(board);
break;
case 2:
player1 = new MachinePlayer(board);
player2 = new HumanPlayer(board);
break;
case 3:
player1 = new HumanPlayer(board);
player2 = new HumanPlayer(board);
break;
default:
throw new IllegalStateException("Unexpected value: " + game_mode);
}
player1.setSign(1);
player2.setSign(2);
System.out.println("");
}
private void initPlayersName(){
/*request name player 1 */
System.out.println(Utils.str_player1Name); /*Scan first name*/
Scanner scan1 = new Scanner(System.in);
String name1 = scan1.next();
player1.setPlayerName(name1);
/*request name player 2 */
System.out.println(Utils.str_player2Name); /*Scan first name*/
Scanner scan2 = new Scanner(System.in);
String name2 = scan2.next();
player2.setPlayerName(name2);
}
public Game() {
System.out.println(Utils.str_start_game);
initBoard();
initGameMode();
initPlayersName();
}
public void start() {
// todo change who starts first
player1.start();
new Thread(new Runnable() {
#Override
public void run() {
try {
Thread.sleep(300);
player2.start();
}catch (Exception e)
{
}
}
}).start();
}
private int requestBoardSize() {
System.out.println(Utils.str_request_board_size);
Scanner scanner = new Scanner(System.in) ;
int i = scanner.nextInt() ;
return i ;
}
}///End of Class

RPG game code error [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I keep getting this error in my code. Can someone fix it and how is the code written? Can it be improved by maybe using setters and getters only?
Exception in thread "main" java.lang.NullPointerException
at Player.attack(Player.java:72)
at Main.main(Main.java:15)
My code:
Player.java
public class Player {
String name;
String race;
int hp;
int power;
int armour;
Weapon weapon;
public Player (String n, String r, int h, int p, int a) {
name = n;
race =r;
hp = h;
power = p;
armour = a;
}
public void setName (String n) {
name = n;
}
public String getName() {
return name;
}
public void setRace (String r) {
race = r;
}
public String getRace() {
return race;
}
public void setHP (int h) {
hp = h;
}
public int getHP() {
return hp;
}
public void setPower (int p) {
power = p;
}
public int getPower() {
return power;
}
public void setArmour (int a) {
armour = a;
}
public int getArmour() {
return armour;
}
public boolean dead() {
return hp <= 0;
}
public boolean equip(Weapon weapon) {
this.weapon = weapon;
return true;
}
public boolean receiveDamage(int i) {
if ((hp - i) > 0) {
hp = hp - i;
return true;
}
hp = 0;
return false;
}
public boolean attack(Player player) {
return player.receiveDamage(weapon.useWeapon());
}
}
Main.java
public class Main {
public static void main(String args[]) {
Player Mensch = new Player("Mensch", "Mensch", 85, 12, 10);
Player Ork = new Player("Shrek", "Ork", 50, 14, 6);
Weapon MenschW = new Weapon("mächtiges Schwert", 15, 100);
Weapon OrkW = new Weapon("große Axt", 7, 100);
Mensch.equip(Mensch.weapon);
Ork.equip(Ork.weapon);
while (!Mensch.dead() && !Ork.dead() ) { //Alternativ: for (player hp >=0)
System.out.println("Mensch gegen Ork " + Mensch.attack(Ork));
if (Mensch.dead() || Ork.dead()) {
break;
}
System.out.println("Mensch gegen Ork " + Ork.attack(Mensch));
}
System.out.println("Ork ist tot: " + Ork.dead());
System.out.println("Mensch ist tot: " + Mensch.dead());
}
}
Weapon.java
import java.util.concurrent.ThreadLocalRandom;
public class Weapon {
String name;
int damage;
int hp;
public Weapon(String string, int d, int hp) {
// TODO Auto-generated constructor stub
}
public void setName (String n) {
name = n;
}
public String getName() {
return name;
}
public void setDamage (int d) {
damage = d;
}
public int getDamage() {
return damage;
}
public void setWHP (int h) {
hp = h;
}
public int getWHP() {
return hp;
}
public int useWeapon() {
if
(broken())
return 0;
hp = hp - 5;
return (damage / 2) + random();
}
private int random() {
return ThreadLocalRandom.current().nextInt(1, damage + 1);
}
private boolean broken() {
return hp <= 0;
}
}
I know its a lot of code but I keep getting the same error, also I'm quite new to java so I would appreciate some tips or suggestions to make my code better or more failsave. The code doesn't do much yet but it will (hopefully) be a simple game soon in which two characters fight eachother with some calculations on damageoutput of each player. In this case a Human and Ork. Feel free to try it out

Change
Mensch.equip(Mensch.weapon); // Mensch.weapon is not initialized in constructor so it is null.
Ork.equip(Ork.weapon); // Ork.weapon is not initialized in constructor so it is null as well.
To
// Use your newly created weapons in the main instead.
Mensch.equip(MenschW );
Ork.equip(OrkW);

Java,Swing! Accept the result and keep playing

I'm new in Java programming, Just made simple Guess a number game and now i need to make GUI. I Just start with some simple showMessage and other stuff but i have a problem. How can i define my Human player result, that it will accept it and game will keep playing. Game is between Human and Robot. Problem starts when i input my number answer and game just stops. I Know now the code is broken, but can you give me some advice or tips what to do ? Thanks
**public class Human extends Player {**
private Player guesser;
private final PrintStream printer;
private final Scanner scanner;
private final String name;
Human(String name, PrintStream printer, Scanner scanner) {
this.name = name;
this.printer = printer;
this.scanner = scanner;
}
#Override
public String getName() {
return name;
}
#Override
public int guess(int n) {
JOptionPane.showInputDialog(String.format ("What do you think about %d?"));
char result = scanner.nextLine().trim().charAt(0);
return result == '=' ? 0 : result == '<' ? -1 : 1;
}
#Override
public int play() {
JOptionPane.showMessageDialog(null, String.format("%s wants your guess:", guesser.getName()), null, JOptionPane.PLAIN_MESSAGE);
int n = Integer.parseInt(scanner.nextLine().trim());
return guesser.guess(n);
}
#Override
public void setGuesser(Player player) {
this.guesser = player;
}
}
**public class Robot extends Player {**
private static final Random RANDOM = new Random();
private final String name;
private Player guesser;
private final PrintStream printer;
private int min = 0;
private int max = Integer.MAX_VALUE;
private int last = 1 + RANDOM.nextInt(1);
private final int guessedNumber;
public Robot(String name, PrintStream printer, int min, int max) {
this.name = name;
this.printer = printer;
this.guessedNumber = min + RANDOM.nextInt(max - min);
}
#Override
public String getName() {
return name;
}
#Override
public int guess(int n) {
int result = Integer.compare(guessedNumber, n);
printer.printf("%s says that %d is %s.%n", getName(), n,
result < 0 ? "too much" : result > 0 ? "not enough" : "just fine"
);
return result;
}
#Override
public int play() {
JOptionPane.showMessageDialog(null,"Robot thinks that Human guessed " + last,"aaa", JOptionPane.PLAIN_MESSAGE);
int guessResult = guesser.guess(last);
if (guessResult != 0) {
if (max - min <= 0) {
throw new IllegalStateException("YOU BLOODY CHEATER! SCREW YOU.");
}
if (guessResult == -1) {
max = last - 1;
} else {
min = last + 1;
}
}
last = min + (max - min) / 2;
return guessResult;
}
#Override
public void setGuesser(Player player) {
this.guesser = player;
}
}

Change your
PrintStream.print method
to JOptionPane.showMessageDialog, or even better put a GUI element like a textbox or label and change the text.

Items not getting add into array

I have 3 classes for this program. I want to print out the total price of the items after shopping, but there is a problem with the output. Though each time shopping are different in the number of items, the output are all the same. Could you please help me to fix it?
Here are my code:
This is the first class:
public class LineItem {
private String name;
private int quantity;
private double pricePerUnit;
/**
*
*/
public LineItem(String name, int quantity, double pricePerUnit) {
this.name = name;
this.quantity = quantity;
this.pricePerUnit = pricePerUnit;
}
public double getCost() {
return quantity*pricePerUnit;
}
public void setQuantity(int newQuantity) {
quantity=newQuantity;
}
}
This is the second class:
import java.util.ArrayList;
public class ShoppingCart {
/**
*
*/
private LineItem[] item;
private int check;
public ShoppingCart() {
item = new LineItem[10];
check = 10;
}
public void add(LineItem newItem) {
int i = 0;
while (item[i] == null && check != 0){
item[i] = newItem;
i++;
check -= check;
}
}
public double getTotalCost() {
double totalCost = 0.0;
for(int i=0; i< item.length;i++){
if(item[i]!=null)
totalCost += item[i].getCost();
}
return totalCost;
}
}
This is the third class:
public class ShoppingCartTester{
public static void main(String[] args){
ShoppingCart singleItemCart = new ShoppingCart();
LineItem item1 = new LineItem("Dove shampoo",1,4.52);
singleItemCart.add(item1);
System.out.println(singleItemCart.getTotalCost());
//
ShoppingCart typicalCart = new ShoppingCart();
item1 = new LineItem("Dove shampoo",1,4.52);
typicalCart.add(item1);
LineItem item2 = new LineItem("apples",5,10.80);
typicalCart.add(item2);
LineItem item3 = new LineItem("avocados",5,20);
typicalCart.add(item3);
LineItem item4 = new LineItem("chocolate",1,4.25);
typicalCart.add(item4);
LineItem item5 = new LineItem("green onions",3,3.49);
typicalCart.add(item5);
System.out.printf("%.2f", typicalCart.getTotalCost());
System.out.println();
}
}
I think the problem is in the add method, but i have no idea how to fix it.
Thank you in advance

I suggest to maintain a global variable with current item in cart (noOfItems),
So that while adding you can directly add new item
So instead of
public void add(LineItem newItem) {
int i = 0;
while (item[i] == null && check != 0){
item[i] = newItem;
i++;
check -= check;
}
}
use
public void add(LineItem newItem){
item[++noOfItems] = newItem;
}
or second way
its better to create ArrayList instead of array of object

Problem is in your Add method:
public void add(LineItem newItem) {
int i = 0; <--- Problem begins
while (item[i] == null && check != 0){
item[i] = newItem;
i++;
check -= check;
}
}
Everytime you are calling add i is getting reset to 0.
Fix1:: To have a list instead of array. Array comes with a fix size which you might want to avoid.

Java blackjack program

So I rewrote it with your suggestion (Todd Hopp) and updated the post in the (*) section in the BlackJack class so you can see how I have it now but I'm still getting the same errors and it is not printing the computePlayerValue for some reason....
ERROR:
Exception in thread "main" java.lang.NumberFormatException: For input string: "King" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at BlackJack.dealCards(BlackJack.java:25)
at PlayCardGame.main(PlayCardGame.java:9)
P.S. I'm was trying to look this up in the book but couldn't find the answer...The BlackJack class is partially source code from an earlier chapter in the book and I couldn't figure out if it was necessary to have super(); in the constructor there? I thought it only had to do if the parent class constructor had an argument? Any help on if it has to be there and if so what it's doing.
BlackJack Class
public class BlackJack extends CardGameFP{
int computePlayerValue;
int computeDealerValue;
int cardValue;
public BlackJack() {
**super();**
player1 = 2;
player2 = 2;
}
public void display() {
System.out.println("BlackJack");
}
//*************************************************************
public int getCardValue(Card card) {
final String rank = card.getRank();
switch (rank) {
case "Ace":
return 1;
case "King":
case "Queen":
case "Jack":
return 10;
default:
return Integer.parseInt(rank);
}
}
public void dealCards() {
//Player 1
System.out.println("Player 1:");
for(int x = 0; x < playerHand; x++) {
shuffle();
System.out.println(fullDeck[x].getRank() + " of " + fullDeck[x].getSuit());
}
cardValue1 = getCardValue(fullDeck[0]);
cardValue2 = getCardValue(fullDeck[1]);
computePlayerValue = cardValue1 + cardValue2;
System.out.println(computePlayerValue);
}
//*************************************************************
//Dealer hand
System.out.println("\nPlayer 2:");
for(int x = 0; x < player2; x++) {
System.out.println(fullDeck[x].getRank() + " of " + fullDeck[x].getSuit() );
shuffle();
}
}
}
public class Card {
protected String suit;
protected int value;
protected String rank;
protected final int LOW_VALUE = 1;
protected final int HIGH_VALUE = 13;
public String getRank() {
return rank;
}
public int getValue() {
return value;
}
public String getSuit() {
return suit;
}
public void setSuit(String st) {
suit = st;
}
public void setValue(int val) {
if(val >= LOW_VALUE && val <= HIGH_VALUE) {
value = val;
}
else {
value = LOW_VALUE;
}
if(val == 1) {
rank = "Ace";
}
else if(val == 11) {
rank = "Jack";
}
else if(val == 12) {
rank = "Queen";
}
else if(val == 13) {
rank = "King";
}
else {
rank = Integer.toString(value);
}
}
}
CardGame Class
abstract public class CardGameFP {
int suitNum = 1;
int val = 1;
int player1;
int player2;
protected final int DECK_OF_CARDS = 52;
Card fullDeck[] = new Card[DECK_OF_CARDS];
protected final int LOW_VALUE = 1;
protected final int HIGH_VALUE = 13;
protected final int HIGH_SUIT = 4;
protected final int CARDS_IN_SUIT = 13;
public abstract void display();
public abstract void dealCards();
public CardGameFP() {
for(int i = 0; i < fullDeck.length; i++) {
fullDeck[i] = new Card();
if(suitNum == 1) {
fullDeck[i].setSuit("Spades");
}
else if(suitNum == 2) {
fullDeck[i].setSuit("Hearts");
}
else if(suitNum == 3) {
fullDeck[i].setSuit("Diamonds");
}
else {
fullDeck[i].setSuit("Clubs");
}
fullDeck[i].setValue(val);
val++;
if(val > HIGH_VALUE) {
suitNum++;
val = 1;
}
}//end for
}
public void shuffle() {
for(int firstCard = 0; firstCard < DECK_OF_CARDS; firstCard++ ) {
firstCard = ((int)(Math.random() * 500) % DECK_OF_CARDS);
int secondCard = ((int)(Math.random() * 500) % DECK_OF_CARDS);
Card temp = fullDeck[firstCard];
fullDeck[firstCard] = fullDeck[secondCard];
fullDeck[secondCard] = temp;
}
}
}
PlayCardGame Class
PlayerCardGame
public class PlayCardGame {
public static void main(String[] args) {
Card CG = new Card();
BlackJack BJ = new BlackJack();
BJ.display();
BJ.dealCards();
}
}

Instead of this line:
cardValue = Integer.parseInt(fullDeck[0].getRank());
I suggest that you create a getCardValue(Card) method:
public int getCardValue(Card card) {
final String rank = card.getRank();
switch (rank) {
case "Ace":
return 1;
case "King":
case "Queen":
case "Jack":
return 10;
default:
return Integer.parseInt(rank);
}
}
and then use:
cardValue = getCardValue(fullDeck[0]);
EDIT: Following the suggestion by #WorldSEnder, you can define a Rank enum:
public enum Rank {
ACE("Ace", 1),
TWO("2", 2),
...
QUEEN("Queen", 10),
KING("King", 10);
private final String displayName;
private final int value;
protected Rank(String displayName, int value) {
this.displayName = displayName;
this.value = value;
}
public String displayName() {
return displayName;
}
public int value() {
return value;
}
}
Then you can modify Card to use a Rank instead of a String for the rank and use:
cardValue = fullDeck[0].getRank().value();

When you call :
cardValue = Integer.parseInt(fullDeck[0].getRank());
the method Interger.parseInt() is attempting to read an int from a string. The problem is that some cards have ranks which themselves are not strings like, King. So when you return the rank of that card, parseInt() doesn't know how to handle King. You should instead be getting the cards actual value using fullDeck[0].getVaule() and parsing that instead. It will be a string between 1 and 13.