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Simple Seat Reservation in Java

package Demo;
import java.util.Scanner;
public class seat_reservation{
public static void main(String[] args) {
Scanner read = new Scanner(System.in);
// Initialization
final int ROWS = 2;
final int COLS = 3;
char [][] seats = new char [ROWS][COLS];
int i, j, seatNum, counter = 0;
char seatLetter = 'A';
int choice = 0;
String seatEnter;
boolean cont = true; // loops of running the program
while( choice != 4 ){
System.out.print( "1. Assign Seats" );
System.out.print( "2. Exit" );
System.out.print( "Select your choice: " );
choice = read.nextInt();
switch( choice ){
case 1:
//Set the value.
for (i=0; i < seats.length; i++) {
for (j=0; j < seats[i].length; j++)
seats[i][j] = seatLetter++;
seatLetter = 'A'; // to reset the value to A for the new loop
}
//To display the list of seats
for (i=0; i < seats.length; i++) {
System.out.print((i+1)+" ");
for (j=0; j < seats[i].length; j++)
System.out.print(seats[i][j]+" ");
System.out.println();
}
//condition
while (counter < 6 && cont) {
do {
System.out.print("Please type the chosen seat(starts with row and column,e.g:2A):" + "");
seatEnter = (read.nextLine()).toUpperCase(); //covert to Upper case
seatNum = Integer.parseInt(seatEnter.charAt(0)+"");
if (seatNum != 0)
seatLetter = seatEnter.charAt(1);
i++;
//if user enters wrong input, error message will appear.
if (seatLetter!='A'){
if (seatLetter!='B'){
if(seatLetter!='C'){
if(seatLetter!='D')
System.out.println ("Invalid! Please enter the correct seat:");
}
}
}
}
//continue to loop until the condition true
while (seatNum < 0 || seatNum > 7 || seatLetter < 'A' || seatLetter > 'D');
if (seatNum == 0) {
cont = false;
} else {
if (seats[seatNum-1][seatLetter-65] == 'X')
System.out.println("Seat have been taken.Please choose another seat:");
else {
seats[seatNum -1][seatLetter-65] = 'X';
counter++;
}
// To display updated lists of seats
for (i=0; i < seats.length; i++) {
System.out.print((i+1)+" ");
for (j=0; j < seats[i].length; j++)
System.out.print(seats[i][j] + " ");
System.out.println();
}
System.out.println(" ") ;
//}
//}
// displays fully booked message
if (counter == 6)
System.out.println("All seats are now fully-booked.");
break;
}
}
case 2://syntax error here
if (counter == 6)
System.out.println( "All seats are now fully-booked." );
System.out.println( "End of Program" );
System.exit(0);
break;
default:
System.out.println("Error input");
break;//syntax error here as well.
}
}
}
}

The problem is caused due to:
choice = read.nextInt();
The scanner.nextInt() only takes the next token from the input. Rest are ignored by it.
So when you're trying to take the next input from this line and process it, the error occurs:
seatEnter = (read.nextLine()).toUpperCase(); //covert to Upper case
seatNum = Integer.parseInt(seatEnter.charAt(0) + "");
As the previous read.nextInt() left the rest except first token, when you hit enter after giving 1 as input, it took only the 1 and the enter or newline token was captured by the read.nextLine(). That is why it got no charAt(0) and thus thrown StringIndexOutOfBoundException.
Try:
choice = Integer.parseInt(read.nextLine());
or,
choice = read.nextInt();
read.nextLine(); // this will capture the residue

Java battleship program not printing board correctly

I am having a problem with my java battleship program not printing the coordinates that the user enters. When the user guesses a spot on the board its supposed to update the space with an "X" if its a hit, if not then the board remains the same. But when a user guesses wrong on my program, it prints everything except the space where the user guessed. I believe that my else statement where the board updates is the problem, but any modification I did resulted in the board not printing anything.
import java.util.Random;
import java.util.Scanner;
class Battleship {
public static char randChar(){
final String alphabet = "ABCDE";
final int N = alphabet.length();
char rand;
Random r = new Random();
rand = alphabet.charAt(r.nextInt(N));
return rand;
}
public static void main (String[] args) throws java.lang.Exception {
char[] letters = {' ', 'A', 'B', 'C', 'D', 'E'};
int[] numbers ={1, 2, 3, 4, 5};
int[][] ships = new int[7][2];
char colGuess;
int rowGuess;
Boolean boardFlag=false;
Scanner scan = new Scanner(System.in);
//creates the board
for (int i = 0 ; i <= 5 ; i++) {
for (int j = 0 ; j <= 5 ; j++) {
if (i == 0) {
System.out.print(letters[j] + " ");
}
else if (j == 0) {
System.out.print(numbers[i - 1]);
}
else {
System.out.print(letters[j] + "" + numbers[i-1]);
}
System.out.print(" ");
}
System.out.println();
}
//assigns ships to random spots
assignShips(ships);
System.out.println("Enter your guess for the column:");
colGuess = scan.next().charAt(0);
//converts to uppercase
colGuess = Character.toUpperCase(colGuess);
System.out.println("Enter your guess for the row:");
rowGuess = scan.nextInt();
//shows player what they entered
System.out.println("you entered: " + (char) colGuess + rowGuess);
//calls method to check for a hit
fire(colGuess, rowGuess, ships);
boardFlag = fire(colGuess, rowGuess, ships);
System.out.println(boardFlag);
//updates the board
for (int i = 0 ; i <= 5 ; i++) {
for (int j = 0 ; j <= 5 ; j++) {
if (i == 0) {
System.out.print(letters[j] + " ");
}
else if (j == 0) {
System.out.print(numbers[i - 1]);
}
else {
if(letters[j] == colGuess && numbers[i - 1] == rowGuess) {
if(boardFlag==true) {
System.out.print(" " + "X");
}
}
else {
System.out.print(letters[j] + "" + numbers[i - 1]);
}
}
System.out.print(" ");
}
System.out.println();
}
}
public static void assignShips(int[][] ships) {
Random random = new Random();
for(int ship = 0; ship < 7; ship++) {
ships[ship][0] = randChar();
ships[ship][1] = random.nextInt(5);
//gives location of ships, for testing purposes
System.out.print("Ship:" + (ship+1)+ " is located at"+(char)ships[ship][0]+ships[ship][1]+"\n");
}
}
//checks user input to see if we have a hit
public static Boolean fire(char colGuess, int rowGuess, int[][] ships) {
Boolean hitFlag=false;
for(int ship = 0; ship < ships.length; ship++){
if(colGuess ==ships[ship][0] && rowGuess == ships[ship][1]){
hitFlag=true;
}
}
if(hitFlag == true) {
System.out.println("we hit em at "+(char)colGuess+rowGuess+" chief!");
}
else {
System.out.println("sorry chief we missed em");
}
return hitFlag;
}
}

The reason its not showing up when you miss is because your net telling it to print anything.
if(letters[j] == colGuess && numbers[i-1] == rowGuess){
if(boardFlag==true) {
System.out.print(" "+"X");
}
}
Your only handling the coordinate the user input if they hit. To fix this you would need an else statement after your if(boardFlag == true)to handle printing if you miss.

The problem is in your update board portion of the code because you don't do anything if the guessed location isn't a hit.
if(letters[j]==colGuess && numbers[i-1]==rowGuess && boardFlag) {
System.out.print(" "+"X");
} else {
System.out.print(letters[j]+""+numbers[i-1]);
}
Full Update Portion:
//updates the board
for (int i = 0 ; i <= 5 ; i++){
for (int j = 0 ; j <= 5 ; j++){
if (i == 0) {
System.out.print(letters[j]+" ");
} else if (j == 0){
System.out.print(numbers[i-1] );
} else {
if(letters[j]==colGuess && numbers[i-1]==rowGuess && boardFlag){
System.out.print(" "+"X");
} else {
System.out.print(letters[j]+""+numbers[i-1]);
}
}
System.out.print(" ");
}
System.out.println();
}

This block (old version):
if(hitFlag==true){
System.out.println("we hit em at "+(char)colGuess+rowGuess+" chief!");
} else {
System.out.println("sorry chief we missed em");
}
Should be (new version):
if(hitFlag==true){
System.out.println("we hit em at "+(char)colGuess+rowGuess+" chief!");
} else {
System.out.println("sorry chief we missed em at " + (char)colGuess+rowGuess);
}
this will print:
sorry chief we missed em at D3 //D3 is a random possible set of coordinates
Rather than:
sorry chief we missed em //Old version
So all you have to add is (char)colGuess+rowGuess, which prints the coordinates of your previous guess.
Comment if you have any questions!

Why is this infinte loop happening?

Guys I really need some help here :(
I need to create a contact list in which I need to be able to create, edit, delete, show and search contacts.
But after I enter number 1 (to include a new number) and type the name and number, it goes to an infinite loop and I was wondering if you guys could help me figure out why it's happening and how to fix it.
I'm pretty sure it has something to do with this block at the end of the code:
while (op!=6)
System.out.println();
But when I remove it, the loop just doesn't happen. Instead of an infinite loop it just doesn't loop at all. I've been trying for literally hours now and I can't seem to figure it out at all.
(also I'm not allowed to use array list here)
Sorry for my english and thank you already!
import java.util.Scanner;
public class Vetor45 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String[] name = new String[1000];
String nname, auxname;
int[] tel = new int[1000];
int ntel, op, cont, i, k, auxtel;
cont = 0;
k = 0;
for (i = 0; i < 1000; i++) {
name[i] = "Empty";
tel[i] = 0;
}
{
System.out.println("contact list:");
System.out.println("1. include a new number");
System.out.println("2. edit a number");
System.out.println("3. delete a number");
System.out.println("4. print all numbers");
System.out.println("5. search by name");
System.out.println("6. exit");
System.out.println("Option:");
op = scanner.nextInt();
System.out.println("");
if (op == 1) {
if (k <= 999) {
while (name[k] != "Empty") {
k++;
}
System.out.println("Enter a name:");
name[k] = scanner.next();
System.out.println("Enter a number:");
tel[k] = scanner.nextInt();
k++;
}
else {
System.out.println("complete");
}
}
else {
if (op == 2) {
i = 0;
System.out.println("enter a name:");
nname = scanner.next();
while (nname != name[i] && i < k - 1) {
i++;
}
if (nname == name[i]) {
System.out.println("enter the new number:");
ntel = scanner.nextInt();
tel[i] = ntel;
}
else {
System.out.println("name not registred");
}
}
else {
if (op == 3) {
k--;
i = 0;
System.out.println("enter a name:");
nname = scanner.next();
while (nname != name[i] && i < k) {
i++;
}
if (nname == name[i]) {
name[i] = "Empty";
tel[i] = 0;
} else {
System.out.println("name not registred");
}
}
else {
if (op == 4) {
for (i = 0; i <= k - 2; i++) {
for (cont = i + 1; cont <= k - 1; cont++) {
if (name[i] == name[cont]) {
auxname = name[i];
name[i] = name[cont];
name[cont] = auxname;
auxtel = tel[i];
tel[i] = tel[cont];
tel[cont] = auxtel;
}
}
}
System.out.println("phone list:");
for (i = 0; i < 1000; i++) {
if (name[i] != "Empty") {
System.out.println("name: " + name[i]);
System.out.println("tel: " + tel[i]);
}
}
}
else {
if (op == 5) {
i = 0;
System.out.println("enter a name:");
nname = scanner.next();
while (nname != name[i] && i < k) {
i++;
}
if (nname == name[i]) {
System.out.println("name: " + nname);
System.out.println("Tel: " + tel);
} else {
System.out.println("name not registred");
}
} else {
if (op == 6) {
System.out.println("exiting");
} else {
System.out.println("option not available");
}
}
}
}
}
}
System.out.println();
}
while (op != 6)
System.out.println();
}
}

You don't even have a do/while loop in this code, here is what a do/while loop loops like:
do{
//loop
}while(op != 6); //don't forget semi colon
You need to develop some standard for braces, and such. As it is right now, it's really hards to read this code.

Yes, as surmised by both you and #Amadan, the while (op != 6) is the problem. In general, when you're looping, something in the loop has to modify something in the condition you're looping on or something in the loop has to modify the normal control flow (so a return, break, etc.), so when you see while (op != 6), you should think "op is the only variable in the condition, so something inside the loop has to modify op or there has to be some other way to get out of the loop."
I think what you want to do is put a do before the big block before the while and then have the while at the end of the block, so you're doing this:
do
{
...
op = scanner.nextInt();
...
} while (op != 6);
That will read an int into op, do some stuff with it, and then bail out if the user entered 6.

The loop while (op!=6) is being run without any changes to op being allowed inside it.
//Rest of the code
System.out.println();
}
while (op!=6)
System.out.println();
}
}
The loop should be evealuated at the beginning of what you need to execute and have everything you want to do in the loop (including changing op) inside it:
for (i=0; i<1000; i++)
{name[i]="Empty"; tel[i]=0;}
while (op!=6)
{
System.out.println("contact list:");
//Rest of the code
You will probably have to move some braces round when you do this also. But I'm not going to go through the whole thing/ that's outside the scope of the question.

int variable remains at 0, while loop not running properly as a result

What I really am stuck with is the second to last variable userGuessDifference. It remains at zero making my second while loop not run properly as it just keeps going back to the first else if statement.
public class GuessingGame {
/**
* #param args
*/
public static void main(String[] args)
{
Scanner keyboard = new Scanner (System.in);
Random generator = new Random();
int difficulty = 0;
int guesses = 0;
int userGuess = 0;
int correctAnswer = 0;
int counter = 0;
int userGuessDifference = (Math.abs(correctAnswer) - Math.abs(userGuess));
boolean flag = false;
System.out.println("We are going to play a number guessing game.");
System.out.println(" ");
System.out.println("Choose your difficulty:");
System.out.println("Pick a number - 10 is easy, 25 is medium, 50 is hard.");
difficulty = keyboard.nextInt();
if (difficulty == 10)
{
guesses = 3;
System.out.println("You have 3 guesses, make them count!");
}
else if (difficulty == 25)
{
guesses = 5;
System.out.println("You have 5 guesses, make them count!");
}
else if (difficulty == 50)
{
guesses = 6;
System.out.println("You have 6 guesses, make them count!");
}
else
{
System.out.println("If you can't follow instructions, I'm going to make this very difficult for you!");
difficulty = (difficulty * 100);
guesses = 1;
}
System.out.println(" ");
System.out.println("Ok, I have my number. Time to play.");
correctAnswer = generator.nextInt(difficulty) + 1;
System.out.println("Pick a whole number between 1 and " + difficulty + ":");
userGuess = keyboard.nextInt();
while (!flag || (counter <= guesses))
{
if (userGuess == correctAnswer)
{
System.out.println("CONGRATS YOU WIN!");
flag = true;
}
else if ((userGuessDifference <= (difficulty * .10)))
{
System.out.println("HOT!");
userGuess = keyboard.nextInt();
counter++;
}
else if ((userGuessDifference < (difficulty * .25)) && (userGuessDifference > (difficulty * .10)))
{
System.out.println("Warm...");
userGuess = keyboard.nextInt();
counter++;
}
else
{
System.out.println("Ice cold.");
userGuess = keyboard.nextInt();
counter++;
}
}
}
}

As #SotiriosDelimanolis wrote, you never reassign userGuessDifference. This should be done inside the while loop.
Moreover, there is another problem with your code: if you guess the number, the program just prints "CONGRATS YOU WIN!" forever, but it seems to me that you wanted to quit from the while loop once the user guesses the number (I guess the flag variable was introduced for this reason).
I slightly changed your code in order to meet this requirement:
import java.util.Random;
import java.util.Scanner;
public class GuessingGame {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
Random generator = new Random();
int difficulty = 0;
int guesses = 0;
int userGuess = 0;
int correctAnswer = 0;
int counter = 0;
System.out.println("We are going to play a number guessing game.");
System.out.println(" ");
System.out.println("Choose your difficulty:");
System.out.println("Pick a number - 10 is easy, 25 is medium, 50 is hard.");
difficulty = keyboard.nextInt();
if (difficulty == 10) {
guesses = 3;
System.out.println("You have 3 guesses, make them count!");
} else if (difficulty == 25) {
guesses = 5;
System.out.println("You have 5 guesses, make them count!");
} else if (difficulty == 50) {
guesses = 6;
System.out.println("You have 6 guesses, make them count!");
} else {
System.out.println("If you can't follow instructions, I'm going to make this very difficult for you!");
difficulty = (difficulty * 100);
guesses = 1;
}
System.out.println(" ");
System.out.println("Ok, I have my number. Time to play.");
correctAnswer = generator.nextInt(difficulty) + 1;
System.out.println("Pick a whole number between 1 and " + difficulty + ":");
userGuess = keyboard.nextInt();
while (counter <= guesses) {
// int userGuessDifference = (Math.abs(correctAnswer) - Math
// .abs(userGuess));
int userGuessDifference = Math.abs(correctAnswer - userGuess);
if (userGuess == correctAnswer) {
System.out.println("CONGRATS YOU WIN!");
break;
}
else if ((userGuessDifference <= (difficulty * .10))) {
System.out.println("HOT!");
}
else if ((userGuessDifference < (difficulty * .25))
&& (userGuessDifference > (difficulty * .10))) {
System.out.println("Warm...");
}
else {
System.out.println("Ice cold.");
}
userGuess = keyboard.nextInt();
counter++;
}
}
}

Checking for user input to be only integers in Java

I'm doing lottery game for my assignment (user inputs 6 number, i will generate 8 unique winning numbers and 2 last numbers are supplementary). I need help with user input checking if input numbers are from 1 to 45 and input must be int, when input is not integer it throws an error.
This programming way is procedure way, how can i change it into object oriented way? I know that I must make methods in another java file and then link it back to this main. Can you suggest me how to do it?
I have tried try and catch, if and else (for input check) but i don't know how to check user input when it's in array. Thank you for help.
Here is my code:
class Lottery {
public static void main ( String[] args ) {
System.out.println("\nWelcome to the Lottery game.");
System.out.println("You can enter numbers from 1 to 45.");
// User input into an array
int[] input = new int[6];
Scanner scanner = new Scanner(System.in);
System.out.println("\nPlease enter your 6 lucky numbers: ");
for(int j = 0; j < 6; j++) {
input[j]=scanner.nextInt();
}
int check = scanner.nextInt();
if(check < 0 && check > 45) {
System.out.println("\nERROR: Please enter only numbers from 1 to 45!");
}
// Printing out unique winning numbers from random generator
System.out.println("\nWinning numbers: ");
MultiRandomGenerator mrg = new MultiRandomGenerator();
int[] set;
set = mrg.getSet();
for (int i = 0; i < set.length; i++) {
System.out.print(set[i] + " ");
}
// Loops for counting how many numbers user has guessed right
int count = 0; // for 6 numbers
int scount = 0; // for 2 last supplementary numbers
for(int i = 0; i < input.length; i++) {
for(int k = 0; k < set.length; k++) {
if (k < 6) {
if (set[k] == input[i]) {
count++;
} else {
if (set[k] == input[i]) {
scount++;
}
}
}
}
}
System.out.print("\n\nYou guessed right " + count + " winning numbers.");
System.out.print("\nYou guessed right " + scount + " suplementary numbers.");
// If statments for printing out winning prizes
if (count == 6) {
System.out.println("\nYou have won 1st price!");
} if (count == 5 && scount == 1) {
System.out.println("\nYou have won 2st price!");
} if (count == 5) {
System.out.println("\nYou have won 3st price!");
} if (count == 4) {
System.out.println("\nYou have won 4st price!");
} if (count == 3 && scount == 1) {
System.out.println("\nYou have won 5st price!");
} if (count == 1 && scount == 2) {
System.out.println("\nYou have won 6st price!");
} else {
System.out.println("\nSorry, you didn't won anything.");
}
}
}

Sample code to go through array and find the invalid user input.
set = mrg.getSet();
String[] userDataStatus = new String[45];
for (int i = 0; i < set.length; i++)
{
try
{
String inputdata = set.get(i);
if(inputdata != null && inputdata.trim().length() > 0)
{
int currentNumber = Integer.parseInt(userdata);
userDataStatus[i] = "Y";//Y represent valid number
}
}
catch (NumberFormatException ex )
{
userDataStatus[i] = "N";//If it throws exception then save as 'N'
}
}
Use the above String array and display error messaage to users.

You can check in your loop, something like
int val;
try
{
input[j] = Integer.parseInt( scanner.nextString() );
}
catch (NumberFormatException ex )
{
}