Develop Reference

Trying to make a chessboard that takes simple string inputs and stores them in Java

I am still new to Java and have been working with 2D arrays recently. What I am trying to do is make a simple 2D grid array of a Chessboard that has the arrays from a1 all the way to h8. The first thing I tried to do is convert the array [8][8] so that the first 8 was characters and the second 8 was integers. What I am currently trying to do is prompt the user and ask them which coordinate they would like to choose (from a1 all the way to h8). When they choose one of the coordinates, I would like them to enter a string (which in the future will be my chess pieces) that will be stored on the board, so that, when I use another class to print these strings, it'll give me an output like "a5 - Lemon (As im not checking to see if the chess piece is a valid piece yet) or "h2 - Queen".
So, to clarify, the program asks the user "Please enter a coordinate (e.g. a5)". "Now, Please enter a piece to be placed on that coordinate" Which then gets stored in that coordinate. When the user types, for example, "Done" I would like all the coordinates that have pieces on them to be revealed as well as what piece was put on them.
Code:
import java.util.Scanner;
public class ChessBoard
{
public static void main(String[] args)
{
char rows = 'a';
String spot;
Scanner scanner = new Scanner(System.in);
int[][] grid = new int [8][8];
for(int i = 0; i < grid.length; i++, rows++)
{
for(int col = 0; col < grid[i].length; col++)
{
System.out.print(rows + "" + (col + 1) + " ");
}
String input = null; // will be changed to a valid position
boolean validCoordinate = false; // will be true if position is valid
while ( ! validCoordinate) {
System.out.println("Enter a coordinate (for example, a5): ");
input = scanner.next();
validCoordinate = input.matches("[a-g][1-8]");
};
// now we now that the input is valid
int col = (int)(input.charAt(0) - 'a');
int row = (int)(input.charAt(1) - '0');
}
}
}
I have used a while loop to continuously prompt the user until they give a correct coordinate, but Im not sure how to prompt the user to enter a piece that gets stored in that coordinate?
Any help would be appreciated!

First of all, in order to store the piece name with the coordinates, you will need a 2D array of strings instead of integers.
After changing that, you take the user input again and then save the coordinates with the piece and save it in the 2d array at said column and row.
Also, the row is retrieved from the character (a-b-c-etc..) and the column from the number and not the way around.
public class ChessBoard
{
public static void main(String[] args)
{
char rows = 'a';
String spot;
Scanner scanner = new Scanner(System.in);
String[][] grid = new String [8][8];
for(int i = 0; i < grid.length; i++, rows++)
{
for(int col = 0; col < grid[i].length; col++)
{
System.out.print(rows + "" + (col + 1) + " ");
}
String input = null; // will be changed to a valid position
boolean validCoordinate = false; // will be true if position is valid
while ( ! validCoordinate) {
System.out.println("Enter a coordinate (for example, a5): ");
input = scanner.next();
validCoordinate = input.matches("[a-g][1-8]");
};
// now we now that the input is valid
int row = input.charAt(0) - 'a';
int col = input.charAt(1) - '1';
String temp = input + " - ";
System.out.println("Insert your piece:");
input = scanner.next();
grid[row][col] = temp + input;
}
System.out.println(Arrays.deepToString(grid));
}
}

What is wrong with method findNumber which performs sequential search in an array to find an index

I am supposed to get an output which shows player's numbers with their walks, outs, and hits, which comes from a .txt file.
I did most of the programming but th output shows -1 for all the players.
Where is the problem ?
Is it the findNumber method?
Or other syntax errors?
public class Baseball8
{
// implementation of main program
public static void main(String[] args) throws FileNotFoundException
{
// 1) connect to input file
Scanner fin = new Scanner(new FileReader("baseball.txt"));
// objects used to store data
final int LIST_LENGTH = 20;
int number = 0, // number, hits, walks, outs
hits,
walks,
outs,
players,
index,
teamSize = 0;
// 2) output descriptive messages
System.out.println("This program tracks a baseball player's number "
+ "and their\nnumber of walks, runs and outs for "
+ "each game in a season.\n");
// 3) declare an array of LIST_LENGTH players
Player[] team = new Player[20];
// 3a) loop over the teamsize
for ( index=0; index<LIST_LENGTH; index++)
// 3b) instantiate the i'th team member
{
team[index] = new Player();
}
// 4) loop on end of file
while (fin.hasNext())
{
// 5) attempt to input the data for the next Player
number = fin.nextInt();
hits = fin.nextInt();
walks = fin.nextInt();
outs = fin.nextInt();
// 6) find the index of this Player's numbEr
number = findNumber(team, index, teamSize);
// 7) if player number is not in the list
if(number == -1 )
{ // 7a) set the Number field for team[teamSize]
team[teamSize].getNumber();
team[teamSize].setNumber(number);
// 7b) set the Hits field for team[teamSize]
team[teamSize].getHits();
team[teamSize].setHits(hits);
// 7c) set the Walks field for team[teamSize]
team[teamSize].getWalks();
team[teamSize].setWalks(walks);
// 7d) set the Outs filed for team[teamSize]
team[teamSize].getOuts();
team[teamSize].setOuts(outs);
// 7e) increase teamSize by 1
teamSize++;
} // 8) else player number is in the list
else
{
// 8a) update the Hits field for team[index]
team[index].setHits(hits + team[index].getHits());
// 8b) update the Walks field for team[index]
team[index].setWalks(walks + team[index].getWalks());
// 8c) update the Outs field for team[index]
team[index].setOuts(outs + team[index].getOuts());
}
}
// 9) display the results
displayArray(team, teamSize);
// 10) disconnect from input file
fin.close();
} // end of main
public static int findNumber(Player[] team, int index,int teamSize )
{ // 1) assume that this player_ number is not in the list
int Save = -1;
// 2) loop over the list length
for (int i=0; i< teamSize - 1; i++)
{
if (index == team[i].getNumber())
Save = i;
}
return Save;
// 3) exit the loop if the number is found
// 4) update the index on successful search
// 5) return either the found index or -1
}
public static void displayArray(Player [] team, int team_size)
{
// 1) display headins of colums
System.out.println("\n\nPlayer\tHits\tWalks\tOuts\n"
+ "------\t----\t-----\t----\n");
// 2) loop over team size
for (int i=0; i < team_size; i++)
{
// 3) display i'th player
System.out.println(team[i]);
}
}
} // end of the class
This is the Player Constructor:
Player()
{
Number= Hits= Walks= Outs = 0;
}
Player ( int Number, int Outs, int Walks, int Hits)
{
Number= Hits= Walks= Outs = 0;
}

By
output shows -1 for all the players.
I suppose you mean the number of all players has been set to -1?
The findNumber-function gives the index of the player with the number you've given as an argument right?? So if you would make the following call:
findNumber(team, 10, 20);
it means you are searching for the player with number 10 in the team-array and you specify that the team-array represents a team with 20 players. The result of this function will then be the index(place) of the player in the team-array.
Well the reason your code is failing is this fragment of code:
number = fin.nextInt();
hits = fin.nextInt();
walks = fin.nextInt();
outs = fin.nextInt();
// 6) find the index of this Player's numbEr
number = findNumber(team, index, teamSize);
// 7) if player number is not in the list
if(number == -1 )
...
You read the number of the player, his hits, walks and outs from the file (so far so good) but then you are searching for the player with the value of index as number and you are storing the index of that player (the result of the findNumber-function in your number-variable. So you replace the number you just read with the result of the findNumber function (that will always return -1 because you're looking for players with as number the value of the index that probably holds a number that doesn't exist in the team and never will because of this error). I don't think that's what you want...
What you probably want is to search the index of the player that has the number you just read from the file (stored in the number variable), store that index in the index variable and then check if that index, now in the index variable, is -1 (meaning, player with number number doesn't exist yet) or not. So the fragment above should be:
number = fin.nextInt();
hits = fin.nextInt();
walks = fin.nextInt();
outs = fin.nextInt();
// 6) find the index of this Player's numbEr
index = findNumber(team, number, teamSize);
// 7) if player number is not in the list
if(index == -1 )
...
I hope this helps!
In the code following this fragment you used your variables correctly.
Good luck!

Monty hall simulation not functioning as expected

import java.util.Scanner;
import static java.lang.System.*;
import static java.lang.Math.*;
import java.util.Random;
public class Montyhall
{
public static void main(String[] args)
{
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter number of attempts:");
int attempts = keyboard.nextInt();/*Decide how many times you want this to
run. The larger the number, the more realistic an answer you will get.*/
int curtains[] = new int[3]; //like the game show, one of these will be a winner
Random rand = new Random(); /*sets the methods up with the same random seed, which
otherwise changes by the milisecond and could influence the response*/
withoutswitch(curtains, attempts, rand);
withswitch(curtains, attempts, rand);
}
public static void withoutswitch(int curtains[], int attempts, Random rand)
{
int nsCorrect=0;
for(int x=0; x < attempts; x++)
{
int winner = rand.nextInt(3);//Sets the winner to 1, leaving the other two at 0.
curtains[winner] = 1; //It then checks to see if they are the same,
int guess = rand.nextInt(3); //a 1/3 chance, roughly.
if(curtains[guess]==1){
nsCorrect++;
}
curtains[0]=0;
curtains[1]=0;
curtains[2]=0;
//the player never changes their decision, so it does not matter if a door is opened.
}
System.out.println("Number of successes with no switch: " + nsCorrect);
}
public static void withswitch(int curtains[], int attempts, Random rand)
{
int ysCorrect=0;
int goat = 0;
for(int x=0; x < attempts; x++)
{
int winner = rand.nextInt(3);
curtains[winner] = 1;
int guess = rand.nextInt(3);
goat = rand.nextInt(3);//one of the doors is opened
while(goat == winner || goat == guess)//the opened door is randomized until
goat = rand.nextInt(3); //it isn't the guess or the winner.
int guess2 = rand.nextInt(3);
while(guess2 == guess || guess2 == goat)
guess2 = rand.nextInt(3);//the second guess goes through a similar process
if(curtains[guess2]==1){
ysCorrect++;
}
curtains[0]=0;
curtains[1]=0;
curtains[2]=0;
}
System.out.println("Number of successes with a switch: " + ysCorrect);
}
}
Sorry it's a bit messy, I'm trying to get back into coding after almost a year hiatus. The first part functions as intended, returning roughly a 1/3 chance of success. The second, however, should be giving me a 2/3 chance, but I'm still getting roughly the same amount right with the switch as with no switch. I looked through the site, and mostly found things outside of Java that I'm not familiar with. This one was very similar, but no one seemed to actually help with the main issue.
What can I do to make the odds more realistic? Advice on cleaning up the code would be appreciated as well.
Edit:Code now functions, I'm now just trying to slim it down.

In your method withoutswitch you need to change
if(guess==1)
nsCorrect++;
to
if (curtains[guess] == 1)
nsCorrect++;
same as in the withswitch method. After each run of the for-loop you need to reset the curtains to 0. Otherwise the previous 1 will be in there and after a few runs the curtains will only contain 1s.
private static void resetCurtains(int[] curtains) {
for (int i = 0; i < curtains.length; i++) {
curtains[i] = 0;
}
}
Call that method after every run within the for-loop.
In addition, i would recommend using {} even if the statements are 1-liner:
if (curtrains[guess] == 1) {
nsCorrect++;
}

Both of your methods do not function as intended.
Your "withoutswitch" method only picks a random number from 0, 1, or 2, and adds to a counter when its 1. In other words, I can simplify your "withoutswitch" method to this:
public static void withoutswitch(int attempts, Random rand) {
int counter = 0;
for (int i = 0; i < attempts; i++) {
if (rand.nextInt(3) == 1) counter++;
}
System.out.println(counter);
}
Your "withswitch" method, believe it or not, does the exact same thing. You start guessing using one variable, then you completely disregard it and do it to a second variable, and check if that is 1. So, it produces the exact same results.
Both of your methods use the "curtains" array, but not correctly. The point of this problem is to put the car behind a random door every time, but you never set your array back to all zeros, and so, after a few runs, it becomes an array of all ones, which definitely isn't what you want.
Here is some pseudocode to help you get started:
number of switch wins = 0
number of stay wins = 0
scan in the number of attempts
loop through each attempt:
make an array {0, 0, 0}
pick a random number (0, 1, or 2), and set that array index to 1 (winning index)
pick a random number (0, 1, or 2), and set it to choice
pick a random number (0, 1, or 2), and set it to the shown door
loop while the door number isn't the choice number or the winning index:
pick a random number (0, 1, or 2) and set it to the shown door
increment stay wins if the choice is equal to the winning index
increment switch wins if (3 - choice - showndoor) is equal to the winning index
print stay wins and switch wins
Note: that last bit of logic determines the index of the switched door, since your only possible indices are 0, 1, and 2, (0 + 1 + 2 = 3), then 3 - the door you chose - the door you were shown = the last door.
Hope this helps!

I would back up and restructure the whole thing. One object for the game, two descendents, one of which simply picks a door, one of which picks and then switches.
I'm not entirely following your switch logic but it's definitely wrong. Monty's logic is if the prize is behind the player's door you open one randomly, otherwise you open one with the goat. Only a single random number is desirable.
Likewise, the player switches. There is only one curtain at this point, no random numbers are needed.
A rough stab at the logic (not Java, not the whole program):
MontyHaulGame
{
int[] Curtains = new int[3];
int Car = Random(3);
int Guess;
Pick();
if (Guess == Car) Wins++;
}
MontyHaulNoSwitch : MontyHaulGame
{
Pick()
{
Guess = Random(3);
}
}
MontyHaulSwitch : MontyHaulGame
{
Pick()
{
Guess = Random(3);
OpenOne();
Switch();
}
OpenOne()
{
if Guess == Car then
Repeat
Monty = Random(3);
Until Monty != Guess;
else
Monty = 1;
While (Monty == Guess) || (Monty == Car)
Monty++;
}
Switch()
{
NewGuess = 1;
While (NewGuess == Guess) || (NewGuess == Monty)
NewGuess++;
Guess == NewGuess;
}
}

JAVA: If/Else/For Methods?! WHAT?

I can't even do the basics. What am I doing wrong?
I need to:
Draw a "X" made up of stars (*). I must prompt for the width of the X in stars.
My requirements for this assignment is:
+1 - prompt for size of X
+4 - draw X of stars (receive +2 if can draw solid square of stars)
I'm using Eclipse by the way!
import java.util.Scanner;
/*
*
*
* Description: Draws a X.
*/
public class Tutorial1
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
int i,j;
System.out.print("Enter size of box: 4 ");
int size = sc.nextInt();
for (i=0; i < size; i++)
{
for (j=0; j < size; j++)
{
if ( (i == 0) // First row
|| (i == size-1) // Last row
|| (j == 0) // First column
|| (j == size-1) ) // Last column
System.out.print("*"); // Draw star
else
System.out.print(" "); // Draw space
}
System.out.println();
}
}
} //

Your program draws a box correctly.
Enter size of box: 4 7
*******
* *
* *
* *
* *
* *
*******
You need to change your code so it draws a cross instead. The code is actually simpler as you have just two lines instead of four.
I would remove the 4 from the prompt as it confusing.
Enter size of box: 7
* *
* *
* *
*
* *
* *
* *

You already know you problem. You stated it yourself: "I can't even do the basics".
Then learn the basics. There is no way around THAT.
This site is not a "write me a piece of code that does X" service. People will help you only with specific questions on a specific problem. Your task is actually beginner stuff that is pretty simple once you grasped the basic concepts. Failing that, any solution we may provide here will be useless to you, since you don't even understand how the problem was solved. Worse, your teach will most likely notice pretty fast that you did not write that on your own. That screws you double - you get charged of cheating and still haven't learned anything.

Here is the skeleton of what you need. The for loops will iterate through the table. The hard part is coming up with the algorithm for deciding which character to print.
public class Tutorial1
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
int i,j;
System.out.print("Enter size of box: ");
size = sc.nextInt();
Tutorial1 t = new Tutorial1();
t.printX(size);
}
private int _size = 0;
public void printX(int size) {
_size = size;
for(int row = 0; row < _size;row++) {
for(int col = 0; col< _size;col++) {
System.out.print(getChar(row,col));
}
System.out.println();
}
}
private String getChar(int row, int col) {
//TODO: create char algorithm
//As a pointer, think about the lines of the X independently and
//how they increment/decrement with the rows
}
}

How can i specify where o board ends?

i have a board([17][17]) and i place words in it giving the row and the column.I want if the position of the word given is bigger than the board,then a message is shown and you should give the row and column again.
**Board class**
......
public void placeWord(char[][] board, String word, int x, int y)
for (int i = 0; i < word.length(); i++)
{
if (y + i >= board[x].length)
{
System.out.println("The board is smaller!!");
Board b=new Board();
int a,r;
System.out.println("Give row and column again");
a=in.nextInt();
r=in.nextInt();
b.placeWord(board, word, a, r);
}
else {
board[x][y + i] = word.charAt(i);
}
}
When i give a=3 and r=5 it still prints me "The board is smaller!!" and want to give new values again.Does anyone know how to fix this?
Edit
**main()**
board b=new board();
String s="abc";
int x=2,y=20;
b.placeWord(Board, s, x, y);
for(int i=0;i<Board.length;i++)//prints the board
{
System.out.println(Board[i]);
}

From a=3 and r=5 I suspect you already failed for placing the word in the first place and entered a new row/column.
In this case the "old" for loop has not finished yet and will continue to place letters (as long as there are some remaining) after the call to b.placeWord(...);.
One way to circumvent this is to break the loop by a simple break; statement after the call to b.placeWord(...);.
Note: the second time you are filling the word into your newly created board b which you discard afterwards (it is never accessed anywhere in the code you showed us). Additionally you might first test if the word fits (can actually be done without a loop: y+word.length()<=board[x].length()) and then fill in the letters. Otherwise the remainders of the failed attempt will stay on the board.

**Board class**
......
public void placeWord(char[][] board, String word, int x, int y)
if (y + word.length() >= board[x].length)
{
// don't loop, ask for another position to put word
System.out.println("The board is smaller!!");
Board b=new Board();
int a,r;
System.out.println("Give row and column again");
a=in.nextInt();
r=in.nextInt();
b.placeWord(board, word, a, r);
} else
{
// already done the checking, don't need to worry here
for (int i = 0; i < word.length(); i++)
{
board[x][y + i] = word.charAt(i);
}
}