How do i check the input is an integer in java

Question

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 are trying to input 100 ages? Where is your attempt to loop? — Scary Wombat, Feb 07 '20 at 02:25
oh i am sorry dont mean it to be an array it supposed to be just an int — Smile Kenny, Feb 07 '20 at 02:31
Does this help? https://stackoverflow.com/questions/5502548/checking-if-a-number-is-an-integer-in-java — Shivam Mohan, Feb 07 '20 at 02:45

score 1 · Accepted Answer · answered Feb 07 '20 at 02:40

1

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");
    }
}

answered Feb 07 '20 at 02:40

Scary Wombat

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To remove “unintentional” space, use AGE.trim()... – Gokul Nath KP Feb 07 '20 at 03:24

Dipankar Baghel · Answer 2 · 2020-02-07T02:55:55.923

1

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.

edited Feb 07 '20 at 02:55

answered Feb 07 '20 at 02:44

Dipankar Baghel

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Works OK for negative ages, but ages can be 0, and also not very portable to other uses of wanting valid `int` input – Scary Wombat Feb 07 '20 at 02:48
yeh you are right I just gave him an idea to check valid int , he can manipulate or use his logic to print integers according to his use cases. Thanks :) – Dipankar Baghel Feb 07 '20 at 02:52
Why is myInt a double? – Scary Wombat Feb 07 '20 at 02:55
oh sorry my bad. I have updated the code :) – Dipankar Baghel Feb 07 '20 at 02:56

score 0 · Answer 3 · answered Feb 07 '20 at 02:35

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");
        }
    }

Does not answer the question – Scary Wombat Feb 07 '20 at 02:41 — Scary Wombat, Feb 07 '20 at 02:41

score 0 · Answer 4 · answered Feb 07 '20 at 05:25

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

How do i check the input is an integer in java

4 Answers4