Develop Reference

Java guess game. How do I use data validation to check if a number is within a certain range?

I need help coding a set of statements of data validation that checks if a user entry is within a range of 0 and 100, and anything the user types that ISNT a non-decimal integer between 1 and 100 should display an error message. Also I need a way to code how I can get a "goodbye" output to only display if the user enters "n" not "n" and "y." N meaning no and y meaning yes.
Heres my code.
import java.util.Scanner;
public class GuessingGameCalc {
private static void displayWelcomeMessage(int max) {
System.out.println("Welome to the Java Guessing Game!");
System.out.println(" ");
System.out.println("I'm thinking of a number between 1 and" + " " + max + " " + "let's see if you guess what it is!");
System.out.println(" ");
}
public static int calculateRandomValue(int max) {
double value = (int) (Math.random() * max + 1);
int number = (int) value;
number++;
return number;
}
public static void validateTheData(int count) {
if( count < 3) {
System.out.println("Good job!");
} else if (count < 7) {
System.out.println("Need more practice.");
} else{
System.out.println("Need way more practice.");
}
}
public static void main(String[] args) {
final int max = 100;
String prompt = "y";
displayWelcomeMessage(max);
int unit = calculateRandomValue(max);
Scanner sc = new Scanner(System.in);
int counter = 1;
while (prompt.equalsIgnoreCase("y")) {
while (true) {
System.out.println("Please enter a number.");
int userEntry = sc.nextInt();
if (userEntry < 1 || userEntry > max) {
System.out.println("Invalid guess! Guess again!");
continue;
}
if (userEntry < unit) {
if ( (unit - userEntry) > 10 ) {
System.out.println("Way Too low! Guess higher!");
} else {
System.out.println("Too low! Guess higher!");
}
} else if (userEntry > unit) {
if( (userEntry - unit) > 10 ){
System.out.println("Way Too high! Guess lower!");
} else {
System.out.println("Too high! Guess lower!");
}
} else {
System.out.println("Congratulations! You guessed it in" + " " + counter + " " + "tries!\n");
validateTheData(counter);
break;
}
counter++;
}
System.out.println("Would you like to try again? Yes or No?");
prompt = sc.next();
System.out.println("Goodbye!");
}
}
}

Instead of using .nextInt() rather use .nextLine(), which returns a String and then parse it to an int and catch the NumberFormatException
So basically you'll have this structure:
try {
int userEntry = Integer.parseInt(sc.nextLine());
...
} catch (NumberFormatException nfe) {
System.out.println("Please enter a valid number.");
}
Oh, just a comment on the rest of your code. You don't really need two while loops, one will be more than sufficient.

Catch invalid input and return to input prompt JAVA

I am very new to Java and as part of my college course I have to write a program that carries out some basic functions. Part of this program is that it needs to calculate the factorial of a number that the user inputs. If the user inputs a negative number then it must prompt for a positive number. I have got it to do this.
But if the user enters a fraction such as 2.2 then the program should present the user with an error and prompt for valid data. I believe some sort or try-catch should be implemented but so far I have had no success in getting this to work, after spending many hours on it. Any ideas how to get the program to catch the InputMismatchException error and prompt user for input again?
The relevant block of code from the program is below...
public static void factorialNumber() {
int factorial = 1;
boolean valid;
int number = 0;
do {
System.out.println("Please enter a number: ");
number = sc.nextInt();
valid = number > 0;
if (!valid) {
System.out.println("ERROR Please enter a positive number");
}
} while (!valid);
if (number < 0) {
System.out.println("***Error***: Please enter a positive number ... ");
factorialNumber();
}
if (number > 0) {
System.out.print("The factorial is: " + number + " ");
}
for (int i = 1; i <= number; i++) {
factorial *= i;
if ((number - i) > 0) {
System.out.print("x " + (number - i) + " ");
}
}
System.out.println("= " + factorial);
}

You can use Double class to parse the user input and then get only correct values. Like this:
public static void factorialNumber() {
int factorial = 1;
boolean valid;
int number = 0;
String userInput;
do {
System.out.println("Please enter a number: ");
userInput = sc.nextLine();
valid = validateUserInput(userInput);
} while (!valid);
number = Double.valueOf(userInput).intValue();
System.out.print("The factorial is: " + number + " ");
for (int i = 1; i <= number; i++) {
factorial *= i;
if ((number - i) > 0) {
System.out.print("x " + (number - i) + " ");
}
}
System.out.println("= " + factorial);
}
private static boolean validateUserInput(String userInput) {
if (userInput == null) {
System.out.println("You should enter a number!");
return false;
}
Double userInputNumber;
try {
userInputNumber = Double.valueOf(userInput);
} catch (Exception e) {
System.out.println("Please enter a valid number value.");
return false;
}
if (userInputNumber <= 0) {
System.out.println("ERROR Please enter a positive number");
return false;
} else if (userInputNumber - userInputNumber.intValue() > 0) {
System.out.println("ERROR You entered a fractional number!");
return false;
}
return true;
}

error msgs after second loop attempt

I'm working on another assignment and am stuck. First off, I realize I probably won't get the results I want from this code, but at the moment I can't run the code to even see how close or far away I am. I'm sure I'm missing something simple and hope that something will pop out to someone here so I can move past this point. My mother tongue is English but I'm living in Sweden and trying to learn code in a Swedish class so I added //for translations.
Again, I am working with very basic code so am not looking for an easy hack, more of just some insight to where I have gone wrong.
My assignment is to ask the user to enter 10 numbers, store those as an array. Then, offer the user 4 options to calculate those numbers and a 5th option to quit the program.
Here's what I have so far:
package inlämningsuppgift3;
import java.util.Scanner;
import java.util.Arrays;
public class Inlämningsuppgift3 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int nr;
int antal = 0;
int[] num = new int[10];
int sum = 0;
int min = 0;
int max = 0;
for (nr = 0; nr < 10; nr++) {
System.out.println("Ange ett tal " + (nr+1) + " : ");
int tal = input.nextInt();
num[nr] = tal;
if (nr == 0) { //first number
min = tal;
max = tal;
}
else { // All other numbers
if (tal > max) { max = tal; }
if (tal < min) { min = tal; }
}
sum = sum + tal;
}
{
// What would you like to do?
System.out.println("Välj vad du vill göra?");
// Show largest number
System.out.println("1: Visa storsta talet.");
// Show smallest number
System.out.println("2: Visa minsta talet.");
// Show average
System.out.println("3: Visa medeltalet.");
// Show all numbers
System.out.println("4: Visa alla inmatade tal.");
// Quit
System.out.println("5: Avsluta");
}
do {
int k = input.nextInt();
if (k == 1) {
// Largest number is:
System.out.println("Storsta talet är: " + max);
}
else if (k == 2) {
// Smallest number is:
System.out.println("Minsta talet är: " + min);
}
else if (k == 3) {
// Average number is:
System.out.println("Medeltalet är: " + sum/10);
}
else if (k == 4) {
// All the entered numbers:
System.out.println("Alla tal: " + num[10] + ", ");
}
else if (k==5) {
// Goodbye
System.out.println("Hej då!");
break;
}
else {
System.out.println("Felaktigt, prova igen.");
// Unrecognized, try again.
}
while (k<5);
}
}
}
I'm getting error on the last 3 } and I'm not sure why. Are they in the wrong place? I've tried moving them around, I've tried deleting them (obviously, didn't help either) I tried changes to my {} placement above in the code and just haven't found a way around this error. Thank you in advance for any input!

java do-while syntax is:
do {
// Statements
}while(Boolean_expression);
so, change it to:
int k = 0;
do {
k = input.nextInt();
if (k == 1) {
System.out.println("Storsta talet är: " + max);
} else if (k == 2) {
System.out.println("Minsta talet är: " + min);
} else if (k == 3) {
System.out.println("Medeltalet är: " + sum / 10);
} else if (k == 4) {
System.out.println("Alla tal: " + num[10] + ", ");
} else if (k == 5) {
System.out.println("Hej då!");//good bye
break;
} else {
System.out.println("Felaktigt, prova igen.");
}
} while (k < 5) ;
and after while line must be two } now.

Hej Hej!
I made the modifications I think like you asked to make it 'just about work'
package Dunno;
import java.util.Scanner;
public class NumberCollector { //No special characters in source files,
//Can get transformed during deployment
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int nr;
int antal =0;
int[] num = new int[10];
int sum = 0;
int min=0;
int max=0;
for (nr=0; nr<10; nr++)
{
System.out.println("Ange ett tal " + (nr+1) + " : ");
int tal = input.nextInt();
num[nr]=tal;
if(nr == 0) //first number
{
min=tal;
max=tal;
}
else //all other numbers
{
if(tal>max)max =tal;
if(tal<min) min=tal;
}
sum = sum + tal;
}
System.out.println("Välj vad du vill göra?");
//what would you like to do?
System.out.println("1: Visa storsta talet.");
//Show largest number
System.out.println("2: Visa minsta talet.");
//show smallest number
System.out.println("3: Visa medeltalet.");//show average
System.out.println("4: Visa alla inmatade tal.");
//show all numbers
System.out.println("5: Avsluta");//quit
while (true) //Moved the stop condition to start of the loop makes it easier to read logically.
{
int k = input.nextInt();
if (k==1)
{
System.out.println("Storsta talet är: " + max);
//largest number is:
}
else if (k==2)
{
System.out.println("Minsta talet är: " + min);
//smallest number is:
}
else if (k==3)
{
System.out.println("Medeltalet är: " + sum/10);
//average number is:
}
else if (k==4)
{
System.out.println("Alla tal: " + num[10] + ", ");
//all the entered numbers:
}
else if (k==5)
{
System.out.println("Hej då!");//good bye
break;
}
else
{
System.out.println("Felaktigt, prova igen.");
//unrecognized, try again.
}
};
}
}
I only had to move around some braces.
It seems to broadly do what you want? It throws an exception if you ask for result 4, I'll leave that to you :)
Maybe this will be a good starting point? Consider replacing the loop with a switch/case condition would be nicer to read and maintain?

How to prevent string from printing repeatedly in while loop?

I'm currently working on some exercises given to me by my teacher. These are for the holidays so I won't be able to ask for help there.
I have this piece of code which creates a multiplication table from an integer defined by the user, ranging from a minimum and maximum also defined by the user.
Before setting any of my variables to the next integer in my Scanner, I do a check to see if the Scanner actually has an integer. This works fine but I don't want it to print out the error message a billion times.
Any tips/tricks or other special ways of getting around this?
public class MultiplicationTable
{
private int intervalMin;
private int intervalMax;
private int multiplier;
private int result;
private Scanner sc;
public MultiplicationTable()
{
multiplier = 0;
intervalMin = 0;
sc = new Scanner(System.in);
while (multiplier == 0)
{
System.out.println("Please enter the integer you wish to show the table for");
if (sc.hasNextInt())
{
multiplier = sc.nextInt();
}
else
{
System.out.println("Input is not an integer\n");
}
}
while (intervalMin == 0)
{
System.out.println("\nPlease enter the integer defining the start of the table");
if (sc.hasNextInt())
{
intervalMin = sc.nextInt();
}
else
{
System.out.println("Input is 0 or not an integer\n");
}
}
while (intervalMax == 0)
{
System.out.println("\nPlease enter the integer defining the end of the table");
if (sc.hasNextInt())
{
int i = sc.nextInt();
if (i > intervalMin)
{
intervalMax = i;
}
else
{
System.out.println("\nEnd integer must be greater than start integer");
}
}
else
{
System.out.println("Input is 0 or not an integer");
}
}
System.out.println("\nTable for integer " + multiplier + " from " + intervalMin + " to " + intervalMax + "\n");
for (int i = intervalMin; i <= intervalMax; i++)
{
result = i * multiplier;
System.out.println(i + " * " + multiplier + " = " + result);
}
}
}

You didn't consume what user entered into the scanner buffer, that's why sc.hasNextInt() keeps getting executed without waiting for the next user input.
The solution is to add sc.nextLine() after the if condition.
For example:
boolean gotInteger = false;
while (!gotInteger) {
System.out.println("Please enter the integer you wish to show the table for");
if (sc.hasNextInt()) {
multiplier = sc.nextInt();
gotInteger = true;
} else {
System.out.println("Input is not an integer\n");
}
sc.nextLine();
}

Pleas try this, just wrap all your code inside try catch:
try {
while (intervalMax == 0) {
System . out . println("\nPlease enter the integer defining the end of the table");
if (sc . hasNextInt()) {
int i = sc . nextInt();
if (i > intervalMin) {
intervalMax = i;
} else {
throw new Exception("\nEnd integer must be greater than start integer");
}
}
}
} catch (Exception e) {
System . out . println(e . getMessage());
}

Java: Exception Help Char and Int

Ok all, I'm stuck again with this code.
I need to put in an Exception that won't allow the user to input 0 (because you can't divide later by 0) and the user cannot enter alpha characters. I am trying to display the message, disregard the wrong input, and loop to allow the user to try again until they put in the acceptable number.
Here is what I have:
package exceptionhandler;
/**
*
* #author Sarah
*/
import java.util.Scanner;
public class ExceptionHandler {
/**
* #param args
* the command line arguments10 10
*/
public static void main(String[] args) throws NumberFormatException {
Scanner in = new Scanner(System.in);
Scanner input = new Scanner(System.in);
System.out.print("Please enter ten values:");
System.out.println();
// Input the data into array from the user.
double[ ] digit = new double[11];
int sum = 0;
//Declare an array
try
{
for (int i = 1; i < digit.length; i++) {
System.out.print("Value " + i + ": ");
digit[i] = (double)in.nextInt();
sum += (int)digit[i];
}
catch (NumberFormatException e)
{
System.out.println("You Can Only Enter Numbers!");
}
}
System.out.println("Total Values in Array:"+ sum);
// Calculate the sum and print the total
System.out.println();
System.out.println("Would you like to divide the values?");
System.out.println("Yes or No to Exit the Program");
String a = input.next();
if(a.equalsIgnoreCase("yes")){
double [] divisionResult = new double[digit.length / 2];
//Division array declared
for (int i = 1; i < digit.length; i += 2)
{
double result = digit[i];
if (result > digit[i + 1])
result = result / digit[i + 1];
else {
result = digit[i + 1] / result;
}
divisionResult [i / 2] = result;
System.out.println(result);
}
}
else if(a.equalsIgnoreCase("no")){
System.exit(0);
}
}
}
I have tried declaring the throw exception and then tried a try..catch. But it is not recognizing catch and try talking to one another... so I know I am doing something wrong, but I can't see where it should go.
Is the Exception in the right place? Should I have done something else? Is my exception written wrong? How can I then move on to prevent the input of zero as well- rethrow?
Help?

It supposed to be InputMismatchException not NumberFormatException to catch an exception upon entering characters and you need to check for 0 if the user input 0 and deduct 1 the current index of the for-loop to let the user try again.
sample:
for (int i = 1; i < digit.length; i++) {
try {
System.out.print("Value " + i + ": ");
digit[i] = (double) in.nextInt();
sum += (int) digit[i];
if(digit[i] == 0.0)
{
System.out.println("You cant enter 0: try again");
--i;
}
} catch (InputMismatchException e) {
System.out.println("You Can Only Enter Numbers!");
--i;
in.nextLine(); //to consume the character
}
}
result:
Please enter ten values:
Value 1: 0
You cant enter 0: try again
Value 1: asd
You Can Only Enter Numbers!
Value 1: