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How do I continue to loop until the user wants to quit?

Java
How do I continue to loop until the user wants to quit? I have tried inserting a do while loop but no matter where I put it, it doesn't seem to work. it keeps giving me an error message. I want to loop this until the user doesn't want to enter a score anymore. so it will continue to prompt for another letter grade until they type a "Y" or "N". Thank you!
import java.util.Scanner;
public class gradeConverter {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int score = 0;
int minimum = 0;
int maximum = 100;
int grade = 0;
System.out.println("Enter letter grade 0-100: ");
score = scan.nextInt();
if (!isValidNumber(score,1,100))
{
System.exit(0);
}
getLetterGrade(score);
}
private static boolean isValidNumber(int number, int minimum, int maximum)
{
return number > minimum && number<=maximum;
}
private static String getLetterGrade(int score)
{
String grade=null;
if(score >=80 && score <90) {
System.out.println("B");//java code tells you that your letter grade is a B if you input a score that is between and includes 90 and 80
grade = "B";
}
else if(score <= 100 && score >= 90) {
System.out.println("A");//java code tells you that your letter grade is a A if you input a score that is between and includes 100 and 90
grade = "A";
}else if(60>score){
System.out.println("F");
grade = "F";
}
return grade;
}
}

You can simply use while loop until the user wants to quit. Add a condition on user prompt input and if the user tries to quit, just break the loop.
Also, you're exiting the system if the user gives invalid input. What you can do is, you can continue the program to make the user give a valid input.
while (true) {
System.out.println("Enter letter grade 0-100: ");
score = scan.nextInt();
if (!isValidNumber(score, minimum, maximum)) {
System.out.println("The input is not in valid range!");
continue;
}
letterGrade = getLetterGrade(score);
System.out.println("The corresponding letter grade is: " + letterGrade);
if (!doContinue(scan)) {
break;
}
}
The do continue function just checks whether the user wants to continue or not. Returns a boolean:
private static boolean doContinue(Scanner sc) {
System.out.println("Do you want to continue? (y/n): ");
String input = sc.next();
return input.toLowerCase().equals("y");
}
Also, instead of printing the grades while checking condition, you can just return it, just as I've done in the above segment:
private static String getLetterGrade(int score) {
if (score >= 80 && score < 90) {
return "B";
} else if (score >= 90 && score <= 100) {
return "A";
} else if (score < 60) {
return "F";
} else {
return "Unknown Grade";
}
}
And I guess you can change the min max range too, for a proper practical input:
private static boolean isValidNumber(int number, int minimum, int maximum) {
return number >= minimum && number <= maximum;
}

import java.util.Scanner;
public class gradeConverter {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
char opt;
int score = 0;
int minimum = 0;
int maximum = 100;
int grade = 0;
do {
System.out.println("Enter letter grade 0-100: ");
score = scan.nextInt();
if (!isValidNumber(score, 1, 100)) {
System.exit(0);
}
getLetterGrade(score);
System.out.println("Do yu wish to continue?: ");
opt = Character.toLowerCase(scan.next().charAt(0));
} while (opt == 'y');
}
private static boolean isValidNumber(int number, int minimum, int maximum) {
return number > minimum && number <= maximum;
}
private static String getLetterGrade(int score) {
String grade = null;
if (score >= 80 && score < 90) {
System.out.println("B");// java code tells you that your letter grade is a B if you input a score that
// is between and includes 90 and 80
grade = "B";
} else if (score <= 100 && score >= 90) {
System.out.println("A");// java code tells you that your letter grade is a A if you input a score that
// is between and includes 100 and 90
grade = "A";
} else if (60 > score) {
System.out.println("F");
grade = "F";
}
return grade;
}
}
The do ... while loop works for this but you might want to refactor your variable declarations to change with newer scores being inputted.

I refactored your code a bit, and added the possibility to say a grade or N in the same field.
I also added the possibility to loop until an incorrect value or a N value is typed, using a simple while condition
Just have a look and feel free to modify it again
import java.util.Scanner;
public class gradeConverter {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int minimum = 1;
int maximum = 100;
String grade;
boolean keep_going = true;
while(keep_going) {
System.out.println("Enter letter grade 0-100: ");
grade = scan.nextLine();
if (!isValidChoice(grade, minimum, maximum)) {
System.out.println("Invalid choice!");
keep_going = false;
break;
}
if(grade.toLowerCase().equals("n"))
keep_going = false;
else
getLetterGrade(Integer.parseInt(grade));
}
}
private static boolean isValidChoice(String value, int minimum, int maximum)
{
if(value.toLowerCase().equals("n"))
return true;
try {
int letter = Integer.parseInt(value);
return letter > minimum && letter<=maximum;
} catch (NumberFormatException e) {
return false;
}
}
private static String getLetterGrade(int score)
{
String grade=null;
if(score >=80 && score <90) {
System.out.println("B");//java code tells you that your letter grade is a B if you input a score that is between and includes 90 and 80
grade = "B";
}
else if(score <= 100 && score >= 90) {
System.out.println("A");//java code tells you that your letter grade is a A if you input a score that is between and includes 100 and 90
grade = "A";
}else if(60>score){
System.out.println("F");
grade = "F";
}
return grade;
}
}

You can scan in a loop and check the entered data for the need to exit it.
I also changed the type of the input value to support this check.
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String input;
int minimum = 0;
int maximum = 100;
int grade = 0;
System.out.println("Enter letter grade 0-100: ");
input = scan.nextLine();
while (!input.equals("y") || !input.equals("n")) {
int score = Integer.parseInt(input);
if (!isValidNumber(score,1,100)) {
getLetterGrade(score);
}
input = scan.nextLine();
}
System.exit(0);
}

How do I simplify this integer validation?

I'm new to Java, and I'm working on a method in my program that checks the users input to be within bounds, not a null value (zero), not a letter, and a positive number. So originally I incorporated two while loops within this method to check for the validity of these inputs, but I would like to simplify it in one loop. I'm getting an error when I input a letter (ex. a) after a few inputs, and I believe it is due to the two different while loops making it more complicated. Can someone help me with this please?
public static void valid(String s, int max)
{
while(sc.hasNextInt() == false) {
System.out.println("That is not correct. Try again:");
sc.nextLine();
}
int value;
while((value= sc.nextInt()) > max || (value= sc.nextInt()) <= 0){
System.out.println("That is not correct. Try again: ");
sc.nextLine();
}
sc.nextLine();
return;
}

You have:
int value;
while((value= sc.nextInt()) > max || (value= sc.nextInt()) <= 0){
System.out.println("That is not correct. Try again: ");
sc.nextLine();
}
Which is doing sc.nextInt() twice, so value does not necessarily have the same value in these two cases and it is also asking you for a number twice.
A fix would be something like this:
int value;
while((value = sc.nextInt()) > max || value <= 0) {
System.out.println("That is not correct. Try again: ");
sc.nextLine();
}
which would make it better but you still have issues. If value is bigger than max, then the loop will iterate again calling nextInt() but this time you have not checked for hasNextInt(). This is why you'd better have everything in one loop. Something like this:
public static void valid(String s, int max) {
while(true) {
if(!sc.hasNextInt()) { //this is the same as sc.hasNextInt() == false
System.out.println("That is not correct. Try again:");
sc.nextLine();
continue; //restart the loop again
} else {
int value = sc.nextInt();
if(value > max || value <= 0) {
System.out.println("That is not correct. Try again:");
sc.nextLine();
continue; //restart the loop from the top - important!
} else {
extendedValidation(value, s);
return;
}
}
}
}

Try something more like (pseudo code):
while valid input not yet received:
if input is an integer:
get integer
if in range:
set valid input received
skip rest of line
extended validation
With a little thought, you should be able use one "print error message" statement. But using two could be arguably better; it can tell the user what they did wrong.

What is the purpose of the String s parameter? Should you be checking that instead of a Scanner input?
Also, don't be surprised by mixing nextInt() and nextLine(). -- Source
I prefer using do-while loops for input before validation.
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int max = 1000;
int val = -1;
String in;
do {
// Read a string
System.out.print("Enter a number: ");
in = input.nextLine();
// check for a number
try {
val = Integer.parseInt(in);
} catch (NumberFormatException ex) {
// ex.printStackTrace();
System.out.println("That is not correct. Try again.");
continue;
}
// check your bounds
if (val <= 0 || val > max) {
System.out.println("That is not correct. Try again.");
continue;
} else {
break; // exit loop when valid input
}
} while (true);
System.out.println("You entered " + val);
// extendedValidation(value, in);
}

I would say that this is a lot closer to what you're looking for, in simple terms...
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
final int MIN = 0;
final int MAX = 10;
Scanner sc = new Scanner(System.in);
int value = -1;
boolean valid;
do {
valid = sc.hasNextInt();
if (valid) {
value = sc.nextInt();
valid = value > MIN && value < MAX;
}
if (!valid) {
System.out.println("Invalid!");
sc.nextLine();
}
} while (!valid);
System.out.println("Valid Value: " + value);
}
}
You should be able to abstract this code to suit your requirements.

Java SecretWord Code

I am making basic java program to hold a secret word (mouse) and allow a user to guess letters. The program will end either when the user guesses all the letters in the word, or when they guess 7 wrong letters. Whenever I type any letter into the program, it will run through it without giving the user an option to enter another letter. What should I add so that it will only run the program once per letter entered? Also if it wasnt quite obvious I am new to coding.
import java.util.Scanner;
public class GuessWord
{
String Secretword="mouse";
String letter;
int index;
private int number;
private int counter;
private String guesses;
Scanner scan = new Scanner(System.in);
public GuessWord()
{
String Secretword="";
String letter = "";
String guesses = "";
int number = 0;
int counter = 0;
int index = 0;
}
public String getLetter(){
System.out.println("Please enter a letter");
letter = scan.next();
return letter;
}
public void calc(){
guesses=letter;
while(number <= 7 && counter<5)
{
if(Secretword.indexOf(letter) != -1)
{
index = Secretword.indexOf(letter);
System.out.println("You entered a letter in the word");
counter++;
}
else
{
System.out.println("You entered an incorrect letter");
number++;
}
guesses=guesses+" " +letter;
System.out.println("The letters you have guessed are:" + guesses);
}
String str;
if(number == 7){
System.out.println("You lose");
}else
{
System.out.println("You win");
}
}
}//class
public class GuessWordR
{
public static void main(String[]args)
{
GuessWord g1 = new GuessWord();
g1.getLetter();
g1.calc();
}//class
}//main

You should use a while loop.
So while some condition is not met keep asking the user to enter a new key.
Perhaps add a new method to the GuessWord Class
public void startGuessing() {
while(hasGuesses /* some boolean flag */) {
getLetter()
getCalc()
}
}
And then call that method in your main method instead of getLetter() and getCalc().
You will need to add a boolean variable to your class to indicate when to exit this while loop and the logic to keep count of the number of failed guesses etc.

Use a boolean flag and run it in a loop. but for that you need to restructure your code as well. First fix the calc() method
public boolean calc() {
guesses = letter;
if (number <= 7 && counter < 5) {
if (Secretword.indexOf(letter) != -1) {
index = Secretword.indexOf(letter);
System.out.println("You entered a letter in the word");
counter++;
} else {
System.out.println("You entered an incorrect letter");
number++;
}
guesses = guesses + " " + letter;
System.out.println("The letters you have guessed are:" + guesses);
}
String str;
if (number == 7) {
System.out.println("You lose");
return true;
} else if (counter == 5) {
System.out.println("You win");
return true;
} else {
return false;
}
}
Your main method should be update like this
public static void main(String[] args) {
GuessWord g1 = new GuessWord();
boolean completed = false;
while (!completed) {
g1.letter = g1.getLetter();
completed = g1.calc();
}
}

you ask user for input unless condition get satisfied instead of asking and calculating once. And read char by char input instead of reading whole string.
something like:
public static void main(String[]args)
{
GuessWord g1 = new GuessWord();
while(number <= 7 && counter<5){
g1.getLetter();
g1.calc();
}
}//class

.length error when trying to use a for loop with an ArrayList

First off I'm sorry for the title I couldn't think of a better way to word it. The actual error is in option 3(whenever I try to add together all the sales in option 1). When I try to use salesList.length to track the size of the array I get cannot find symbol- variable length I'm very new to using array lists and that method worked for me in an earlier array but that array wasn't dynamic. Is there a specific way to track the length of a dynamic array list?
import java.util.*;
public class CustomerTest
{
public static void main(String[] args)
{
double totalSales = 0;
ArrayList<String> nameList;
nameList = new ArrayList<String>();
ArrayList<Double> salesList;
salesList = new ArrayList<Double>();
Scanner myScanner = new Scanner(System.in);
boolean done = true;
do
{
System.out.println("1) Add a new customer \n 2) Print all customers \n 3) Compute and print the total sales \n 4) Quit");
int choice = Integer.parseInt(myScanner.nextLine());
if (choice == 1)
{
System.out.print("Add a new customer ");
String answer = myScanner.nextLine();
nameList.add(answer);
System.out.print("Enter their sales ");
String answer2 = myScanner.nextLine();
double answer3 = Double.parseDouble(answer2);
salesList.add(answer3);
}
else if(choice == 2)
{
System.out.println("Customers: " + nameList);
System.out.println("Sales: " + salesList);
}
else if(choice == 3)
{
for(int i = 0; i < salesList.length; i++)
{
totalSales = totalSales + salesList[i];
}
System.out.println(totalSales);
}
else if(choice == 4)
{
System.out.println("Goodbye *Bows gracefully*");
done = false;
}
else
System.out.println("Invalid Choice");
}
while (done);
System.exit(0);
}
}

Change it to salesList.size();. Unlike arrays, the length of an ArrayList is not a directly accessible field.

Array have the length field
ArrayList doesnot have the length field type Use size()

use salesList.size(). unlike arrays you cannot use salesList.lenght

else if (choice == 3) {
for (int i = 0; i < salesList.size(); i++) {
totalSales += salesList.get(i);
}
System.out.println(totalSales);
}
Replace choice 3 with this and it should work.

your code is having bugs: Change the else if(choice==3) {} conditional part to following. you cannot use salesList.length, it can be done using salesList.size() and pleas change salesList[i] to salesList.get(i).
else if(choice == 3)
{
for(int i = 0; i < salesList.size(); i++)
{
totalSales += salesList.get(i);
}
System.out.println(totalSales);
}

Java: Easier Way to Re-prompt user for input when invalid data is entered

I am creating a simple program using the java language which uses a bunch of similar methods to retrieve information from the user. The method i have used to deal with the user entering invalid data seems very incorrect to me, so i am seeking professional guidance on how to better handle invalid data.
I have attempted to search for similar questions but have found none.
This is a sample of one of my methods:
public static int getInput()
{
int temp = 1;
do
{
System.out.println("Answers must be between 1 and 15");
temp = reader.nextInt();
if(temp >=1 && temp <= 15)
{
return temp;
}
else
{
System.out.println("Please enter a valid value");
}
}while(temp > 15 || temp < 1);
//This value will never be reached because the do while loop structure will not end until a valid return value is determined
return 1;
}//End of getInput method
Is there a better way to write this method?
This question is entirely made up so i can learn a better method to implement in my future programs.
Is using a labeled break statement acceptable? such as:
public static int getInput()
{
int temp = 1;
start:
System.out.println("Answers must be between 1 and 15");
temp = reader.nextInt();
if(temp >=1 && temp <= 15)
{
return temp;
}
else
{
System.out.println("Please enter a valid value");
break start;
}
}
Thank you very much in advance.

You have forgotten to check the case, that non-number values are entered (Scanner#nextInt throws a java.util.InputMismatchException). One suggestion which takes care of that issue, is less redundant and more flexible:
public static int getInput(int min, int max) {
for (;;) {
Scanner scanner = new Scanner(System.in);
System.out.println(String.format("Answers must be between %s and %s", min, max));
try {
int value = scanner.nextInt();
if (min <= value && value <= max) {
return value;
} else {
System.out.println("Please enter a valid value");
}
} catch (InputMismatchException e) {
System.out.println("Input was no number");
}
}
}

If you are just worried about the return that is not used and double checking temp you can do something like
public static int getInput()
{
while(true)
{
System.out.println("Answers must be between 1 and 15");
temp = reader.nextInt();
if(temp >=1 && temp <= 15)
{
return temp;
}
else
{
System.out.println("Please enter a valid value");
}
}
}//End of getInput method