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.
Related
This question already has answers here:
How to type a string to end a integer Scanning process in Java
(3 answers)
Closed 2 years ago.
Trying to use scanner to recognize both integers and strings, and stopping user input if a certain string is inputted.
Scanner myObj = new Scanner(System.in);
System.out.println("Enter number of students");
int numberof = myObj.nextInt();
Need to make it so if the user types "end", the scanner no longer takes user input. I can't put the line int numberof = myObj.nextInt(); in a loop or something and limit the variable scope, as i'm using that value of numberof throughout the rest of my code.
You can use Scanner#next and then parse integers if needed. I wouldn't recommend just directly using Scanner#nextInt.
Scanner sc = new Scanner(System.in);
do {
System.out.println("Enter number of students");
String next = sc.next();
if (next.equals("end")) break;
else {
try {
int num = Integer.parseInt(next);
} catch (NumberFormatException e) {
System.out.println("Please enter a valid input");
}
}
} while (true);
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:
How to handle infinite loop caused by invalid input (InputMismatchException) using Scanner
(5 answers)
Closed 4 years ago.
Im trying to create a simple program where user enters an integer and if its not an integer it prints that an error occured and the program loops until user enters an integer. I found this try-catch solution but it doesn`t work properly. If user doesnt enter an integer the program will infinitly loop.
What would the correct solution be?
Scanner input = new Scanner(System.in);
int number;
boolean isInt = false;
while(isInt == false)
{
System.out.println("Enter a number:");
try
{
number = input.nextInt();
isInt = true;
}
catch (InputMismatchException error)
{
System.out.println("Error! You need to enter an integer!");
}
}
You're close.
It's easier to fail on parsing a string than it is to try to get an int from the Scanner since the scanner will block until it gets an int.
Scanner input = new Scanner(System.in);
int number;
boolean isInt = false;
while (isInt == false) {
System.out.println("Enter a number:");
try {
number = Integer.parseInt(input.nextLine());
isInt = true;
} catch (NumberFormatException error) {
System.out.println("Error! You need to enter an integer!");
}
}
This question already has answers here:
How to handle infinite loop caused by invalid input (InputMismatchException) using Scanner
(5 answers)
Closed 7 years ago.
I'm simply want to get a valid int value for age
But when user enters an string, why i cant get an int again?
Here is my code:
public static void getAge() throws InputMismatchException {
System.out.print("Enter Your age: ");
try {
age = in.nextInt();
} catch (InputMismatchException imme) {
System.out.println("enter correct value for age:");
in.nextInt(); // why this not works?
}
}
Enter Your age: hh
enter correct value for age:
Exception in thread "main" java.util.InputMismatchException
I want to request to enter a valid int value until a valid input enters.
If nextInt() fails to parse the input as an int, it leaves the input in the buffer. So the next time you call nextInt() it is trying to read the same garbage value again. You must call nextLine() to eat the garbage input before trying again:
System.out.print("Enter your age:");
try {
age = in.nextInt();
} catch (InputMismatchException imme) {
System.out.println("Enter correct value for age:");
in.nextLine(); // get garbage input and discard it
age = in.nextInt(); // now you can read fresh input
}
You probably want to arrange this in a loop too, so that it will keep asking repeatedly so long as the input is unsuitable:
System.out.print("Enter your age:");
for (;;) {
try {
age = in.nextInt();
break;
} catch (InputMismatchException imme) {}
in.nextLine();
System.out.println("Enter correct value for age:");
}
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.