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How to avoid having to declare a new scanner inside do while loop

I have created a program that allows a user to keep guessing numbers until they either guess the correct number or enter end. I have used a do-while loop to do this. When I create a new scanner inside the loop body it works as expected. However if I create it outside the loop body, it works fine if the input is integers or the first input is end However if the input end follows integer inputs it doesn't
pick up the nextLine() until the next loop. Is there a way to do this without having to creat a new scanner object each time.
private static void guessingGame() {
Scanner sc = new Scanner(System.in);
int answer = 7;
String input = "";
int number = 0;
do {
//Scanner sc = new Scanner(System.in);
System.out.print("Guess a number between 1 and 10 or end to finish ");
System.out.println("input at start is: " + input);
boolean b = sc.hasNextInt();
if(b) {
number = sc.nextInt();
System.out.println("number is: " + number); //for testing code
}else {
input = sc.nextLine();
System.out.println("input is: " + input); //for testing code
}
if (number == answer) {
System.out.println("Correct Guess");
break;
}else {
if(input.equals("end")) System.out.println("Hope you enjoyed the game");
else System.out.println("Incorrect Guess, try again ");
}
System.out.println("input before while is: " + input); //for testing code
}while(number != answer && !(input.equals("end")));
}
Example output for when end follow an integer input:enter code here
number is: 3
Incorrect Guess, try again
input before while is:
Guess a number between 1 and 10 or end to finish input at start is:
end
input is:
Incorrect Guess, try again
input before while is:
Guess a number between 1 and 10 or end to finish input at start is:
input is: end
Hope you enjoyed the game
input before while is: end

you can solve this by using a while loop .
See the following code.
private static void guessingGame() {
Scanner sc = new Scanner(System.in);
int answer = 7;
String input = "";
int number = 0;
while(!input.equals("end")) {
//Scanner sc = new Scanner(System.in);
System.out.print("Guess a number between 1 and 10 or end to finish ");
System.out.println("input at start is: " + input);
boolean b = sc.hasNextInt();
if(b) {
number = sc.nextInt();
System.out.println("number is: " + number); //for testing code
}else {
input = sc.next(); //Edited here . Changed nextLine() to next().
System.out.println("input is: " + input); //for testing code
}
if (number == answer) {
System.out.println("Correct Guess");
break;
}else {
if(input.equals("end")) System.out.println("Hope you enjoyed the game");
else System.out.println("Incorrect Guess, try again ");
}
System.out.println("input before while is: " + input); //for testing code
}
}
In here , at first , input will always be empty String . On while loop, it gets assigned to your String input i.e, end . Till it encounters end , your loop will be running.
Edited
Change input=sc.nextLine(); to input=sc.next(); . This is because , your scanner waits for next Line and doesn't consider "end" as input string .

how to check and display an error message if the input is not a number in java

How to have a try and catch statement to validate the input in variable odd is a number else print an error message? I am new in java programming. Appreciate any help
import java.util.Scanner;
public class ScenarioB{
public static void main (String[]args){
int odd;
Scanner scan = new Scanner(System.in);
System.out.print("Enter An Odd Number\n");
odd = scan.nextInt();
}
}

The Scanner class has a method for this
Scanner in = new Scanner(System.in);
int num;
if(in.hasNextInt()){
num = in.nextInt();
System.out.println("Valid number");
}else{
System.out.println("Not a valid number");
}
Output 1:
8
Valid number
Output 2:
a
Not a valid number

Your code will like bellow:
try {
int scannedNumber;
Scanner scan = new Scanner(System.in);
System.out.print("Enter An Odd Number\n");
String userInput = scan.nextLine();
System.out.println("You pressed :" + userInput);
scannedNumber = Integer.parseInt(userInput);
if (scannedNumber % 2 == 0) {
throw new Exception("Not an odd number");
}
System.out.println("You pressed odd number");
} catch (Exception e) {
System.out.println("" + e.getMessage());
}
Here after taking input as String. Then cast as integer. If casting failed then it will throw NumberFormatException. If it is a number then check is it odd? If not odd then it is also throwing an exception.
Hope this will help you.
Thanks :)

How to validate user's input, and read-in their input again if it invalidates, using try-catch?

I want to validate user input using the exception handling mechanism.
For example, let's say that I ask the user to enter integer input and they enter a character. In that case, I'd like to tell them that they entered the incorrect input, and in addition to that, I want them to prompt them to read in an integer again, and keep doing that until they enter an acceptable input.
I have seen some similar questions, but they do not take in the user's input again, they just print out that the input is incorrect.
Using do-while, I'd do something like this:
Scanner reader = new Scanner(System.in);
System.out.println("Please enter an integer: ");
int i = 0;
do {
i = reader.nextInt();
} while ( ((Object) i).getClass().getName() != Integer ) {
System.out.println("You did not enter an int. Please enter an integer: ");
}
System.out.println("Input of type int: " + i);
PROBLEMS:
An InputMismatchException will be raised on the 5th line, before the statement checking the while condition is reached.
I do want to learn to do input validation using the exception handling idioms.
So when the user enters a wrong input, how do I (1) tell them that their input is incorrect and (2) read in their input again (and keep doing that until they enter a correct input), using the try-catch mechanism?
EDIT: #Italhouarne
import java.util.InputMismatchException;
import java.util.Scanner;
public class WhyThisInfiniteLoop {
public static void main (String [] args) {
Scanner reader = new Scanner(System.in);
int i = 0;
System.out.println("Please enter an integer: ");
while(true){
try{
i = reader.nextInt();
break;
}catch(InputMismatchException ex){
System.out.println("You did not enter an int. Please enter an integer:");
}
}
System.out.println("Input of type int: " + i);
}
}

In Java, it is best to use try/catch for only "exceptional" circumstances. I would use the Scanner class to detect if an int or some other invalid character is entered.
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
boolean gotInt = false;
while (!gotInt) {
System.out.print("Enter int: ");
if (scan.hasNextInt()){
gotInt = true;
}
else {
scan.next(); //clear current input
System.out.println("Not an integer");
}
}
int theInt = scan.nextInt();
}
}

Here you go :
Scanner sc = new Scanner(System.in);
boolean validInput = false;
int value;
do{
System.out.println("Please enter an integer");
try{
value = Integer.parseInt(sc.nextLine());
validInput = true;
}catch(IllegalArgumentException e){
System.out.println("Invalid value");
}
}while(!validInput);

You can try the following:
Scanner reader = new Scanner(System.in);
System.out.println("Please enter an integer: ");
int i = 0;
while(true){
try{
i = reader.nextInt();
break;
}catch(InputMismatchException ex){
System.out.println("You did not enter an int. Please enter an integer:");
}
}
System.out.println("Input of type int: " + i);

Beginner Java program

I'm a beginner with Java and I have the following code:
public class test
{
public static void main(String[] args)
{
int a ;
String b;
Scanner input = new Scanner(System.in);
try {
System.out.println("Enter a: ");
a = input.nextInt();
} catch(Exception e )
{
System.out.println("That is not a number!");
}
System.out.println("Enter your name: ");
b = input.next();
System.out.println("Hello " + b);
}
}
when I give a string instead of int the code performs further and I receive this result:
"Enter a:
fsd
That is not a number!
Enter your name:
Hello fsd"
How can I make an interruption after the catch? (I have already try with a new Scanner after catch, but I think there are also another ways)
Thanks in advance!
LE: I have managed to do that with the "input.next();". I actually wanted to tip in another value for the string b, but the program takes automatically the int a instead of a new value and prints "Hello vsd", although vsd was the input for a.

As stated by the documentation, the Scanner will not advance to the next token if the current token does not match an integer's format. Therefore, if an exception is not thrown, the token in not consumed, and you just get it the next time you call a nextXYZ method.
Scans the next token of the input as an int. This method will throw InputMismatchException if the next token cannot be translated into a valid int value as described below. If the translation is successful, the scanner advances past the input that matched.
Instead of throwing and catching the exception (which is a heavy operation), you could use hasNextInt() to check it in advance:
int a ;
String b;
Scanner input = new Scanner(System.in);
System.out.println("Enter a: ");
if (input.hasNextInt()) {
a = input.nextInt();
} else {
System.out.println("That is not a number!");
// Skip the token so you won't get it later:
input.nextLine();
}
System.out.println("Enter your name: ");
b = input.next();
System.out.println("Hello " + b);

Try this
public class Test{
public static void main(String[] args){
int a ;
String b;
Scanner input = new Scanner(System.in);
try {
System.out.println("Enter a: ");
a = input.nextInt();
System.out.println("Enter your name: ");
b = input.next();
System.out.println("Hello " + b);
}
catch(Exception e ){
System.out.println("That is not a number!");
}
}
}

Just modify your catch block as follow:
catch(Exception e )
{
System.out.println("That is not a number!");
System.exit(0);
}

You should try to use the following block
input.hasNextInt()
instead as it doesn't require you to use a catch or throw exception, but rather if and else statements.
Your code still carries on because the catch block simply catches the exception and replaces it with a System.out.println that prints "That is not a number!"
} catch(Exception e )
{
System.out.println("That is not a number!");
}
Upon doing so the code continues to
System.out.println("Enter your name: ");
b = input.next();
System.out.println("Hello " + b);

How to loop user input until an integer is inputted?

I'm new to Java and I wanted to keep on asking for user input until the user enters an integer, so that there's no InputMismatchException. I've tried this code, but I still get the exception when I enter a non-integer value.
int getInt(String prompt){
System.out.print(prompt);
Scanner sc = new Scanner(System.in);
while(!sc.hasNextInt()){
System.out.println("Enter a whole number.");
sc.nextInt();
}
return sc.nextInt();
}
Thanks for your time!

Take the input using next instead of nextInt. Put a try catch to parse the input using parseInt method. If parsing is successful break the while loop, otherwise continue.
Try this:
System.out.print("input");
Scanner sc = new Scanner(System.in);
while (true) {
System.out.println("Enter a whole number.");
String input = sc.next();
int intInputValue = 0;
try {
intInputValue = Integer.parseInt(input);
System.out.println("Correct input, exit");
break;
} catch (NumberFormatException ne) {
System.out.println("Input is not a number, continue");
}
}

Shorter solution. Just take input in sc.next()
public int getInt(String prompt) {
Scanner sc = new Scanner(System.in);
System.out.print(prompt);
while (!sc.hasNextInt()) {
System.out.println("Enter a whole number");
sc.next();
}
return sc.nextInt();
}

Working on Juned's code, I was able to make it shorter.
int getInt(String prompt) {
System.out.print(prompt);
while(true){
try {
return Integer.parseInt(new Scanner(System.in).next());
} catch(NumberFormatException ne) {
System.out.print("That's not a whole number.\n"+prompt);
}
}
}

Keep gently scanning while you still have input, and check if it's indeed integer, as you need:
String s = "This is not yet number 10";
// create a new scanner
// with the specified String Object
Scanner scanner = new Scanner(s);
while (scanner.hasNext()) {
// if the next is a Int,
// print found and the Int
if (scanner.hasNextInt()) {
System.out.println("Found Int value :"
+ scanner.nextInt());
}
// if no Int is found,
// print "Not Found:" and the token
else {
System.out.println("Not found Int value :"
+ scanner.next());
}
}
scanner.close();

As an alternative, if it is just a single digit integer [0-9], then you can check its ASCII code. It should be between 48-57 to be an integer.
Building up on Juned's code, you can replace try block with an if condition:
System.out.print("input");
Scanner sc = new Scanner(System.in);
while (true) {
System.out.println("Enter a whole number.");
String input = sc.next();
int intInputValue = 0;
if(input.charAt(0) >= 48 && input.charAt(0) <= 57){
System.out.println("Correct input, exit");
break;
}
System.out.println("Input is not a number, continue");
}