Develop Reference

Why does my if input.equals("Quit") not quit correctly?

public void addPizza() throws FileNotFoundException {
Menu menu = new Menu();
Map<Integer, Pizza> pizzaMenu = menu.getPizzaMenu();
boolean exit = false;
while (!exit) {
String input1;
String input2;
System.out.println("What pizza");
input1 = sc.nextLine();
System.out.println("How many pizzas");
input2 = sc.nextLine();
if (input1.equals("Quit") || input1.equals("quit") || input2.equals("Quit") || input2.equals("quit")) {
exit = true;
} else {
Pizza pizza = pizzaMenu.get(Integer.parseInt(input1));
Integer quantity = Integer.parseInt(input2);
OrderLineItem orderLine = new OrderLineItem(pizza,quantity,"");
listOfOrderLineItems.add(orderLine);
Hello. I've got the above code, however my loop will not exit correctly.
As it stands now, It'll ask you "What pizza" -> input Quit -> "How many pizzas" -> input Quit.
The idea is that it just quits the loop after typing Quit once, either in the What pizza or How many pizzas.
IMO it should exit after just one "Quit", since the if statement should set the boolean to true?
Hope anyone can help.
Kind regards

Of course it behaves like this. Your if to check for the input "quit" comes after the second question.
The easiest change for this program to behave like you want is to put the same quit-check again after the first question and then instead of using the exit-flag make a break statement.
The while could then be a "while(true)".
So in short it would look like this:
while (true) {
String input1 = readline("What pizza");
if (isQuit(input1)) {
break;
}
String input2 = readLine("How many pizzas");
if (isQuit(input2)) {
break;
}
// do your stuff
}

Instead of changing the value of variable
exit
you can just use the
break
command and keep the while-loop running until it breaks.

Java Infinite loop

Can someone please advise why the inner loop of the code below will not exit?
I've added an inner loop to check if input from the user of of a particular value and if not prompts for the correct input. When debugging the code and passing in a value which should force the loop to end it doesn't although I can see the correct value in the variable:
while (finished.equalsIgnoreCase("n")) {
System.out.println("Enter a persons name");
names = in.nextLine();
writer.println(names);
System.out.println("Finished? (Y/N)");
finished = in.nextLine();
while( !finished.equalsIgnoreCase("y") || !finished.equalsIgnoreCase("n")) {
System.out.println("Invalid choice; (Y/N)");
finished = in.nextLine();
}
}

Every string is either not not equal to y or not equal to n. You probably meant to use the && operator:
while(!finished.equalsIgnoreCase("y") &&
!finished.equalsIgnoreCase("n")) {
// Code...

exit program do-while loop in java

I am working on a java program. Right now everything is totally working, and all my functionality is there. However, the part I am stuck on is how to exit out of the program in a do-while loop. I must be getting the syntax wrong.
Basically, I set a switch done which reacts to a user's input. Right now, it's working and loops through the program, but it does not exit if I say "no" to continuing.
Here is the part of the code this is happening:
public void main() {
String userInput;
boolean done = true;
Scanner keyboard = new Scanner(System.in);
do {
System.out.println("Welcome to Hangman!");
System.out.println("Do you want to play?");
userInput = keyboard.next();
if (userInput.equals("Yes") || userInput.equals("yes") || userInput.equals("y") || userInput.equals("Y")) {
done = false;
} else if (userInput.equals("n") || userInput.equals("no") || userInput.equals("NO") || userInput.equals("No")) {
done = true;
}
while (!done) {
System.out.println(getDisguisedWord());
System.out.println("Guess a letter: ");
String guess = keyboard.next();
makeGuess(guess);
if (gameOver()) {
String ui;
System.out.println("Do you want to play again?");
ui = keyboard.next();
if (ui.equals("Yes") || ui.equals("yes") || ui.equals("y") || ui.equals("Y")) {
done = false;
} else {
done = true;
}
}
}
} while(done);
}
any tips on how I could handle this better?

Your problem isn't what you think it is. To compare Strings, you need to use their built-in equals() method: ui.equals("Y"). Using == to compare them will always return false. For more information, see How do I compare strings in Java?.
Also, you need to flip your done = true and done = false statements (if the user says yes to playing again, they aren't done yet).
Finally, I would recommend changing your keyboard.next() calls to keyboard.nextLine() calls, or else you may run into weird issues, especially if the user enters input that includes whitespace.
EDIT: I noticed some more issues. You're while loop should be while(!done) instead of while(done). Also, I would get rid of your do-while loop, because the while loop is already allowing the user to play as many times as they want, so it is unnecessary.

boolean flag = true;
Scanner sc = new Scanner(System.in);
do{
System.out.println("***********************************************************");
System.out.println("Welcome to the School Admissions App !!! Press X for exit");
System.out.println("***********************************************************");
System.out.println("Enter the Student Name: ");
String student_name=sc.next();
System.out.println("press y to use this application again. press x to exit from this application ");
String input_user=sc.next();
if(input_user.equalsIgnoreCase("y")){
flag=true;
}else{
flag=false;
System.out.println("Thanks for using it.");
}
}while(flag);

U should use equals method for comparing string value in if statment. ui.equals("yes").

Java .nextLine() repeats line

Everything of my guessing game is alright, but when it gets to the part of asking the user if he/she wants to play again, it repeats the question twice. However I found out that if I change the input method from nextLine() to next(), it doesn't repeat the question. Why is that?
Here is the input and output:
I'm guessing a number between 1-10
What is your guess? 5
You were wrong. It was 3
Do you want to play again? (Y/N) Do you want to play again? (Y/N) n
Here is the code:(It is in Java)
The last do while loop block is the part where it asks the user if he/she wants to play again.
import java.util.Scanner;
public class GuessingGame
{
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
boolean keepPlaying = true;
System.out.println("Welcome to the Guessing Game!");
while (keepPlaying) {
boolean validInput = true;
int guess, number;
String answer;
number = (int) (Math.random() * 10) + 1;
System.out.println("I'm guessing a number between 1-10");
System.out.print("What is your guess? ");
do {
validInput = true;
guess = input.nextInt();
if (guess < 1 || guess > 10) {
validInput = false;
System.out.print("That is not a valid input, " +
"guess again: ");
}
} while(!validInput);
if (guess == number)
System.out.println("You guessed correct!");
if (guess != number)
System.out.println("You were wrong. It was " + number);
do {
validInput = true;
System.out.print("Do you want to play again? (Y/N) ");
answer = input.nextLine();
if (answer.equalsIgnoreCase("y"))
keepPlaying = true;
else if (answer.equalsIgnoreCase("n"))
keepPlaying = false;
else
validInput = false;
} while (!validInput);
}
}
}

In your do while loop, you don't want the nextLine(), you just want next().
So change this:
answer = input.nextLine();
to this:
answer = input.next();
Note, as others have suggested, you could convert this to a while loop. The reason for this is that do while loops are used when you need to execute a loop at least once, but you don't know how often you need to execute it. Whilst it's certainly doable in this case, something like this would suffice:
System.out.println("Do you want to play again? (Y/N) ");
answer = input.next();
while (!answer.equalsIgnoreCase("y") && !answer.equalsIgnoreCase("n")) {
System.out.println("That is not valid input. Please enter again");
answer = input.next();
}
if (answer.equalsIgnoreCase("n"))
keepPlaying = false;
The while loop keeps looping as long as "y" or "n" (ignoring case) isn't entered. As soon as it is, the loop ends. The if conditional changes the keepPlaying value if necessary, otherwise nothing happens and your outer while loop executes again (thus restarting the program).
Edit: This explains WHY your original code didn't work
I should add, the reason your original statement didn't work was because of your first do while loop. In it, you use:
guess = input.nextInt();
This reads the number off the line, but not the return of the line, meaning when you use:
answer = input.nextLine();
It immediately detects the leftover carriage from the nextInt() statement. If you don't want to use my solution of reading just next() you could swallow that leftover by doing this:
guess = input.nextInt();
input.nextLine();
rest of code as normal...

The problem really lies in a completely different segment of code. When in the previous loop guess = input.nextInt(); is executed, it leaves a newline in the input. Then, when answer = input.nextLine(); is executed in the second loop, there already is a newline waiting to be read and it returns an empty String, which activates the final else and validInput = false; is executed, to repeat the loop (and the question).
One solution is to add an input.nextLine(); before the second loop. Another is to read guess with nextLine() and then parse it into an int. But this complicates things as the input could not be a correct int. On a second thought, the code already presents this issue. Try entering a non-numeric response. So, define a function
public static int safeParseInt(String str) {
int result;
try {
result= Integer.parseInt(str) ;
} catch(NumberFormatException ex) {
result= -1 ;
}
return result ;
}
And then replace your first loop with:
do {
validInput= true ;
int guess= safeParseInt( input.nextLine() ) ;
if( guess < 1 || guess > 10 ) {
validInput= false ;
System.out.print("That is not a valid input, guess again: ");
}
} while( !validInput );
PS: I don't see any problem with do-while loops. They are part of the language, and the syntax clearly indicates that the condition is evaluated after the body is executed at least one time. We don't need to remove useful parts of the language (at least from practice) just because others could not know them. On the contrary: if we do use them, they will get better known!

validInput = false;
do {
System.out.print("Do you want to play again? (Y/N) ");
answer = input.next();
if(answer.equalsIgnoreCase("y")){
keepPlaying = true;
validInput = true;
} else if(answer.equalsIgnoreCase("n")) {
keepPlaying = false;
validInput = true;
}
} while(!validInput);
I changed the coding style as I find this way more readable.

Your problem is that nextInt will stop as soon as the int ends, but leaves the newline in the input buffer. To make your code correctly read the answer, you'd have to enter it on the same line as your guess, like 5SpaceYReturn.
To make it behave more than one would expect, ignore the first nextLine result if it contains only whitespace, and just call nextLine again in that case without printing a message.

I believe the output of input.nextLine() will include the newline character at the end of the line, whereas input.next() will not (but the Scanner will stay on the same line). This means the output is never equal to "y" or "n". Try trimming the result:
answer = input.nextLine().trim();

Why is else statement a infinite loop?

I am fairly new to Java and I am trying to work on my data validation. The code runs fine when I use valid data, but when I put in a string instead of an integer the code just loops forever. It just loops the, "Bad input. Please enter a number." Thanks in advance!
//Get input from user
System.out.print("What is your name (Last, First)? ");
String name = scan.nextLine();
System.out.print("enter a date:");
String datein = scan.nextLine();
boolean valid = false;
while (valid != true)
{
System.out.print("Electricity used (KW):");
if (scan.hasNextDouble())
{
electricityUsed = scan.nextDouble();
valid = true;
}
else
System.out.println("Bad input. Please enter a number.");
}

because hasNextDouble always returns false.
here is the doc. You answer your own question :
but when I put in a string instead of an integer

To fix it add a scan.nextLine() to your else branch.

A simpler approach is to use the following.
System.out.print("Electricity used (KW):");
while(!scan.hasNextDouble()) {
scan.nextLine();
System.out.println("Bad input. Please enter a number.");
System.out.print("Electricity used (KW):");
}
double electricityUsed = scan.nextDouble();