Question

In Java, I need help adding a print statement if the user chooses an already used slot. Everything I have tried has failed.

// Tic Tac Toe program that plays the game with user
// Renee Waggoner
// July 26, 2019
// Special Requirements: None
package tic_tac_toe;
import java.util.*;
class TicTacToe
{
   char ttt[][] = new char[3][3];
   static final char player1 = 'O';
   static final char player2 = 'X';
   Scanner scan =new Scanner(System.in);

   String playerID(char player)
   {
       // Prints the identity of the player
       // For example:
       // player2: X
       if (player == player1)
           return "player1: " + player;
       else
           return "player2: " + player;
   }
  
   void getPlayerInput(char player)
   {
       // ******* Details to fill in ************

       // Prompt the user for a cell input. Make sure its a legal
       // cell designator. Also make sure the cell doesn't already
       // have a player in it. Prompt the user again in the case
       // of any problem. Once a valid spot has been found,
       // you will issue a statement like:
       char choice;
       System.out.println("Entering Input For:" + playerID(player));

       System.out.println("enter in cell [a, b, ... i]");
       choice = scan.next().charAt(0);

       switch(choice)
       {
       case 'a':ttt[0][0] = player;break;
       case 'b':ttt[0][1] = player;break;
       case 'c':ttt[0][2] = player;break;
       case 'd':ttt[1][0] = player;break;
       case 'e':ttt[1][1] = player;break;
       case 'f':ttt[1][2] = player;break;
       case 'g':ttt[2][0] = player;break;
       case 'h':ttt[2][1] = player;break;
       case 'i':ttt[2][2] = player;break;
       }

   }
  
   boolean gameIsDraw()
   {
       // ******* Details to fill in ************
       // If all ttt entries have been taken return true
       // otherwise return false
       for(int i = 0; i < ttt.length; i++)
           for(int j = 0; j < ttt [i].length; j++)
               if( ttt [i][j] == ' ')
                   return false;
       return true;
   }
  
   boolean winner(char player)
   {
       // ******* Details to fill in ************
       // Check to see if the parameter player has won
       // Winning means that player shows up in a line of
       // three. The line can be a column, row or a diagonal
       // Return true if player is a winner, otherwise return false.
       for(int i = 0; i < 3; i++)
          

           if(ttt[i][0] == player && ttt[i][1] == player && ttt[i][2] == player)
               return true;

       for(int i = 0; i < 3; i++)

           if(ttt[0][i] == player && ttt[1][i] == player && ttt[2][i] == player)
               return true;

       if(ttt[0][0] == player && ttt[1][1] == player && ttt[2][2] == player)
           return true;

       if(ttt[2][0] == player && ttt[1][1] == player && ttt[0][2] == player)
           return true;

       return false;
   }
  
   void displayBoard()
   {
   // ******* Details to fill in ************
       // game board spacing
   System.out.println("===============================e");
   System.out.println("---a-----b-----c---");
System.out.println("| "+ttt[0][0]+" | "+ttt[0][1]+" | "+ttt[0][2]+" |\n");
System.out.println("---d-----e-----f---");
System.out.println("| "+ttt[1][0]+" | "+ttt[1][1]+" | "+ttt[1][2]+" |\n");
System.out.println("---g-----h-----i---");
System.out.println("| "+ttt[2][0]+" | "+ttt[2][1]+" | "+ttt[2][2]+" |\n");
System.out.println("-------------------");
     
   }
  
   void newgame()
   {
       char currPlayer = player1;
       for(int i = 0; i < 3; i++)
           for(int j = 0; j < 3; j++)
               ttt [i][j] =' ';
       boolean continueOn = true;
       while (continueOn)
       {
           displayBoard();
           if (gameIsDraw())
           {
               System.out.println("******** Game Ends in Draw");
               continueOn = false;
           }
           else
           {
               getPlayerInput(currPlayer);
               if (winner(currPlayer))
               {
                   System.out.println("******** We have a winner: " + playerID(currPlayer));
                   // calling displayBoard method
                   displayBoard();   
                   continueOn = false;
               }
               else
               {
                   if (currPlayer == player1) currPlayer = player2;
                   else currPlayer = player1;
               }
           }
       }
   }
   public static void main(String[] args)
   {
       TicTacToe game = new TicTacToe();
       String str;
       do
       {
           game.newgame();
           System.out.println("Do you want to play Tic-Tac-Toe (y/n)?");
           str = game.scan.next();
       } while ("y".equals(str));
       // otherwise prints Bye
       System.out.println("Bye");
   }
}

Answer 1

import java.util.*;
class TicTacToe
{
char ttt[][] = new char[3][3];
static final char player1 = 'O';
static final char player2 = 'X';
Scanner scan =new Scanner(System.in);

String playerID(char player)
{
// Prints the identity of the player
// For example:
// player2: X
if (player == player1)
return "player1: " + player;
else
return "player2: " + player;
}
  
void getPlayerInput(char player)
{
// ******* Details to fill in ************

// Prompt the user for a cell input. Make sure its a legal
// cell designator. Also make sure the cell doesn't already
// have a player in it. Prompt the user again in the case
// of any problem. Once a valid spot has been found,
// you will issue a statement like:
char choice;
System.out.println("Entering Input For:" + playerID(player));

while(true) {
   System.out.println("enter in cell [a, b, ... i]");
choice = scan.next().charAt(0);

int flag=0;

switch(choice)
{
case 'a':
   if(ttt[0][0] != player1 || ttt[0][0] != player2) {
       ttt[0][0] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[0][0]));
   }
   break;
case 'b':
   if(ttt[0][1] != player1 || ttt[0][1] != player2) {
       ttt[0][1] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[0][1]));
   }
   break;
case 'c':
   if(ttt[0][2] != player1 || ttt[0][2] != player2) {
       ttt[0][2] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[0][2]));
   }
   break;
case 'd':
   if(ttt[1][0] != player1 || ttt[1][0] != player2) {
       ttt[1][0] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[1][0]));
   }
   break;
case 'e':
   if(ttt[1][1] != player1 || ttt[1][1] != player2) {
       ttt[1][1] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[1][1]));
   }
   break;
case 'f':
   if(ttt[1][2] != player1 || ttt[1][2] != player2) {
       ttt[1][2] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[1][2]));
   }
   break;
case 'g':
   if(ttt[2][0] != player1 || ttt[2][0] != player2) {
       ttt[2][0] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[2][0]));
   }
   break;
case 'h':
   if(ttt[2][1] != player1 || ttt[2][1] != player2) {
       ttt[2][1] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[2][1]));
   }
   break;
case 'i':
   if(ttt[2][2] != player1 || ttt[2][2] != player2) {
       ttt[2][2] = player;
       flag=1;
   }else {
       System.out.println("Slot is already chosen by "+playerID(ttt[2][2]));
   }
   break;
default:
   System.out.println("Please enter a valid slot");
}

if(flag == 1) {
   break;
}
}

}
  
boolean gameIsDraw()
{
// ******* Details to fill in ************
// If all ttt entries have been taken return true
// otherwise return false
for(int i = 0; i < ttt.length; i++)
for(int j = 0; j < ttt [i].length; j++)
if( ttt [i][j] == ' ')
return false;
return true;
}
  
boolean winner(char player)
{
// ******* Details to fill in ************
// Check to see if the parameter player has won
// Winning means that player shows up in a line of
// three. The line can be a column, row or a diagonal
// Return true if player is a winner, otherwise return false.
for(int i = 0; i < 3; i++)
  

if(ttt[i][0] == player && ttt[i][1] == player && ttt[i][2] == player)
return true;

for(int i = 0; i < 3; i++)

if(ttt[0][i] == player && ttt[1][i] == player && ttt[2][i] == player)
return true;

if(ttt[0][0] == player && ttt[1][1] == player && ttt[2][2] == player)
return true;

if(ttt[2][0] == player && ttt[1][1] == player && ttt[0][2] == player)
return true;

return false;
}
  
void displayBoard()
{
// ******* Details to fill in ************
// game board spacing
System.out.println("===============================e");
System.out.println("---a-----b-----c---");
System.out.println("| "+ttt[0][0]+" | "+ttt[0][1]+" | "+ttt[0][2]+" |\n");
System.out.println("---d-----e-----f---");
System.out.println("| "+ttt[1][0]+" | "+ttt[1][1]+" | "+ttt[1][2]+" |\n");
System.out.println("---g-----h-----i---");
System.out.println("| "+ttt[2][0]+" | "+ttt[2][1]+" | "+ttt[2][2]+" |\n");
System.out.println("-------------------");

}
  
void newgame()
{
char currPlayer = player1;
for(int i = 0; i < 3; i++)
for(int j = 0; j < 3; j++)
ttt [i][j] =' ';
boolean continueOn = true;
while (continueOn)
{
displayBoard();
if (gameIsDraw())
{
System.out.println("******** Game Ends in Draw");
continueOn = false;
}
else
{
getPlayerInput(currPlayer);
if (winner(currPlayer))
{
System.out.println("******** We have a winner: " + playerID(currPlayer));
// calling displayBoard method
displayBoard();   
continueOn = false;
}
else
{
if (currPlayer == player1) currPlayer = player2;
else currPlayer = player1;
}
}
}
}
public static void main(String[] args)
{
TicTacToe game = new TicTacToe();
String str;
do
{
game.newgame();
System.out.println("Do you want to play Tic-Tac-Toe (y/n)?");
str = game.scan.next();
} while ("y".equals(str));
// otherwise prints Bye
System.out.println("Bye");
}
}