This question already has answers here:
How to use java.util.Scanner to correctly read user input from System.in and act on it?
(1 answer)
Java.util.scanner error handling
(2 answers)
Closed 1 year ago.
I need to write code where the program fails and throws an exception if the second input on a line is a String rather than an Integer. I am confused as to how to compare if the input is a string or an int and I am also struggling on how to use a try/catch statement.
import java.util.Scanner;
import java.util.InputMismatchException;
public class NameAgeChecker {
public static void main(String[] args) {
Scanner scnr = new Scanner(System.in);
String inputName;
int age;
inputName = scnr.next();
while (!inputName.equals("-1")) {
// FIXME: The following line will throw an InputMismatchException.
// Insert a try/catch statement to catch the exception.
age = scnr.nextInt();
System.out.println(inputName + " " + (age + 1));
inputName = scnr.next();
}
}
Instead of
age = scnr.nextInt();
Try
try {
age = scnr.nextInt();
System.out.println(inputName + " " + (age + 1));
}
catch(InputMismatchException e) {
System.out.println("Please enter a valid integer");
}
Related
This question already has answers here:
How to get the user input in Java?
(29 answers)
Closed 2 years ago.
I am trying to figure out how to read input from the console in Java that would behave exactly the same as the following C++ code:
while(cin >> input)
I essentially need to keep reading the console one integer at a time, and only stop when the user enters no more integers.I am able to read integers one at a time, but cannot figure out how to get it to stop executing once the user passes an empty line. Thanks!
Scanner scanner = new Scanner(System.in);
// find the next int token and print it
// loop for the whole scanner
while (scanner.hasNext()) {
// if the next is a int, print found and the int
if (scanner.hasNextInt()) {
System.out.println("Found :" + scanner.nextInt());
}
// if no int is found, print "Not Found:" and the token
System.out.println("Not Found :" + scanner.next());
}
You can use the Scanner nextLine() method and check for integers:
import java.util.*;
class TextNum {
public static void main(String[] args) {
int n;
String s;
Scanner in = new Scanner(System.in);
while (true) {
s = in.nextLine();
//Do something with this
System.out.println("This is :" + s + ":");
try {
n = Integer.parseInt(s);
} catch (Exception e) {
break;
}
}
}
}
This question already has answers here:
How to loop user input until an integer is inputted?
(5 answers)
Closed 3 years ago.
In my program I want an integer input by the user. I want an error message to be show when user inputs a value which is not an integer.
And How can I do this in loop. i am just a beginner please help me.
//code that i already try
Scanner input = new Scanner(System.in);
int age;
String AGE ;
System.out.print("\nEnter Age : ");
AGE = input.nextLine();
try{
age = Integer.parseInt(AGE);
}catch (NumberFormatException ex){
System.out.print("Invalid input " + AGE + " is not a number");
}
You use an while loop and break on sucess
int age;
while (true) { // wil break on sucess
Scanner input = new Scanner(System.in);
System.out.print("\nEnter Age : ");
String AGE = input.nextLine();
try{
age = Integer.parseInt(AGE);
break;
}catch (NumberFormatException ex){
System.out.print("Invalid input " + AGE + " is not a number");
}
}
This is the better way to check user input is integer or Not -
public static void onlyInteger() {
int myInt = 0;
System.out.println(" Please enter Integer");
do {
while (!input.hasNextInt()){
System.out.println(" Please enter valid Integer :");
input.next();
}
myInt = input.nextInt();
}while (myInt <= 0);
}
Hope this will help.
If you are trying to capture the age input as an integer, you would not need the integer array as such
'int age [] = new int [100];'
You can use Scanner's nextInt() method to capture integer input.
This will throw InputMismatchException exception in case the input is not an integer.Try below code.
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter Age: ");
try {
int number = input.nextInt();
System.out.println("Age entered " + number);
} catch (InputMismatchException e) {
System.out.println("Incorrect Input for Age.Please enter integer Integer value");
}
}
To check the input is an integer or any number :
Step 1 is to Read the input as Java Object, then
Object o = new Integer(33);// or can be new Float(33.33)...
if(o instanceof Number) {
System.out.println(o +" is number");// do your thing here
}
The abstract class Number is the superclass of platform classes representing numeric values that are convertible to the primitive types byte, double, float, int, long, and short.
JavaDoc Number
This question already has answers here:
Scanner close after use
(2 answers)
Closed 3 years ago.
When I run my code, it will run fine up to the line "scanner.close()".
After than, when I run the "SumTenNumbers()" method... it will run the first line of the while loop once and crash with the "NoSuchElementException"...
When I remove the code above the line calling the method, it runs fine...
Why does this occur, and how can I solve it?
This is the code:
public class Main
{
public static void main(String[] args)
{
// we use the class "scanner" for input data
Scanner scanner = new Scanner(System.in); //System.in allows you to type input data into the console which can be returned into the console
System.out.println("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Your name is " + name);
System.out.println("Enter your year of birth: ");
boolean isInt = scanner.hasNextInt();
if (isInt)
{
int yearOfBirth = scanner.nextInt();
int age = 2019 - yearOfBirth;
if (age >= 0 && age <= 120)
{
System.out.println("You are " + age + " years old");
}
else
{
System.out.println("Invalid year of birth");
}
}
else
{
System.out.println("Unable to parse year of birth");
}
scanner.close(); // we must close scanner
SumTenNumbers();
}
public static void SumTenNumbers()
{
var reader = new Scanner(System.in);
int sum = 0;
int count = 1;
while (count < 11)
{
System.out.println("Enter number " + count + ": ");
boolean valid = reader.hasNextInt();
if (valid)
{
int userNum = reader.nextInt();
sum += userNum;
count++;
}
else
{
reader.next();
System.out.println("INVALID");
}
}
System.out.println(sum);
reader.close();
}
}
This is how it looks when I run the code...
Enter your name:
Siddharth
Your name is Siddharth
Enter your year of birth:
2001
You are 18 years old
Enter number 1:
Exception in thread "main" java.util.NoSuchElementException
at java.base/java.util.Scanner.throwFor(Scanner.java:937)
at java.base/java.util.Scanner.next(Scanner.java:1478)
at com.company.Main.SumTenNumbers(Main.java:64)
at com.company.Main.main(Main.java:39)
Process finished with exit code 1
the line reader.close() closes the Scanner and, with it, System.in.
After that, you cannot read from stdin (System.in) anymore.
In order to prevent this you can:
use only one Scanner object and close it after using it the last time
close System.in after using it the last time (using a Scanner or System.in.close())
close System.in at the end of your Program
never close System.in (Problem: other Processes cannot use the resource, stdin can also be a File, a Network Connection or something else)
I am having trouble with entering non-integers into an integer field. I am only taking precautions so that if another person uses/works on my program they don't get this InputMismatchException.
When I enter a non-digit character into the input variable, I get the above error. Is there any way to compensate for this like one could do for a NullPointerException when it comes to strings?
This code is redacted just to include the relevant portions causing the problem.
import java.util.Scanner;
class MyWorld {
public static void main(String[] args) {
Scanner user_input = new Scanner(System.in);
int input = 0;
System.out.println("What is your age? : ");
input = user_input.nextInt();
System.out.println("You are: " +input+ " years old");
}
}
You can use an if statement to check if user_input hasNextInt(). If the input is an integer, then set input equal to user_input.nextInt(). Otherwise, display a message stating that the input is invalid. This should prevent exceptions.
System.out.println("What is your age? : ");
if(user_input.hasNextInt()) {
input = user_input.nextInt();
}
else {
System.out.println("That is not an integer.");
}
Here is some more information about hasNextInt() from Javadocs.
On a side note, variable names in Java should follow the lowerMixedCase convention. For example, user_input should be changed to userInput.
You can add a try-catch block:
import java.util.Scanner;
class MyWorld {
public static void main(String[] args) {
Scanner user_input = new Scanner(System.in);
int input = 0;
System.out.println("What is your age? : ");
try{
input = user_input.nextInt();
}catch(InputMisMatchException ex)
System.out.println("An error ocurred");
}
System.out.println("You are: " +input+ " years old");
}
}
If you want to provide the user to enter another int you can create a boolean variable and make a do-while loop to repeat it. As follows:
boolean end = false;
//code
do
{
try{
input = user_input.nextInt();
end = true;
}catch(InputMisMatchException ex)
System.out.println("An error ocurred");
end = false;
System.out.println("Try again");
input.nextLine();
}
}while(end == false);
This is a try-catch block. You need to use this if you want to be sure of not making the program-flow stop.
try {
input = user_input.nextInt();
}
catch (InputMismatchException exception) { //here you can catch that exception, so program will not stop
System.out.println("Integers only, please."); //this is a comment
scanner.nextLine(); //gives a possibility to try giving an input again
}
Test using hasNextInt().
Scanner user_input = new Scanner(System.in);
System.out.println("What is your age?");
if (user_input.hasNextInt()) {
int input = user_input.nextInt();
System.out.println("You are " + input + " years old");
} else {
System.out.println("You are a baby");
}
Use Scanner's next() method to get data instead of using nextInt(). Then parse it to integer using int input = Integer.parseInt(inputString);
parseInt() method throws NumberFormatException if it is not int, which you can handle accordingly.
This question already has answers here:
Determine if a String is an Integer in Java [duplicate]
(9 answers)
user input check int only
(4 answers)
Closed 9 years ago.
I'm trying to use while loop to ask the user to reenter if the input is not an integer
for eg. input being any float or string
int input;
Scanner scan = new Scanner (System.in);
System.out.print ("Enter the number of miles: ");
input = scan.nextInt();
while (input == int) // This is where the problem is
{
System.out.print("Invalid input. Please reenter: ");
input = scan.nextInt();
}
I can't think of a way to do this. I've just been introduced to java
The issue here is that scan.nextInt() will actually throw an InputMismatchException if the input cannot be parsed as an int.
Consider this as an alternative:
Scanner scan = new Scanner(System.in);
System.out.print("Enter the number of miles: ");
int input;
while (true) {
try {
input = scan.nextInt();
break;
}
catch (InputMismatchException e) {
System.out.print("Invalid input. Please reenter: ");
scan.nextLine();
}
}
System.out.println("you entered: " + input);
The javadocs say that the method throws a InputMismatchException if the input doesn;t match the Integer regex. Perhaps this is what you need?
So...
int input = -1;
while(input < 0) {
try {
input = scan.nextInt();
} catch(InputMismatchException e) {
System.out.print("Invalid input. Please reenter: ");
}
}
as an example.