How can I check if an input is a integer or String, etc.. in JAVA?

Question

I am wondering how I can check if a user\'s input is a certain primitive type (I mean integer, String, etc... I think it\'s called primitive type?). I want a user to input s

Answer 1

You may try this with Regex:

String input = "34";
if(input.matches("^\\d+(\\.\\d+)?")) {
  //okay
} else {
  // not okay !
}

Here,

^\\d+ says that input starts with a digit 0-9,

()? may/or may not occur

\\. allows one period in input

Answer 2

Scanner input = new Scanner (System.in);

if (input.hasNextInt()) System.out.println("This input is of type Integer.");
else if (input.hasNextFloat()) System.out.println("This input is of type Float.");
else if (input.hasNextLine()) System.out.println("This input is of type string."); 
else if (input.hasNextDouble()) System.out.println("This input is of type Double."); 
else if (input.hasNextBoolean()) System.out.println("This input is of type Boolean.");  

  else if (input.hasNextLong())
    System.out.println("This input is of type Long."); 

Answer 3

Hate to bring this up after 6 years but I found another possible solution.

Currently attending a coding bootcamp and had to solve a similar problem. We introduce booleans and change their values depending on the result of the try/catch blocks. We then check the booleans using simple if statements. You can omit the prints and input your code instead. Here's what it looks like:

import java.io.IOException;
import java.util.Scanner;

public class DataTypeFinder {
    public static void main(String[] args) throws IOException {
        Scanner scan = new Scanner(System.in);
        String input = "";

        while (true) { //so we can check multiple inputs (optional)
            input = scan.nextLine();

            if ("END".equals(input)) { //a way to exit the loop
                break;
            }

            boolean isInt = true; //introduce boolean to check if input is of type Integer
            try { // surround with try/catch
                int integer = Integer.parseInt(input); //boolean is still true if it works
            } catch (NumberFormatException e) {
                isInt = false; //changed to false if it doesn't
            }

            boolean isDouble = true; //same story
            try {
                double dbl = Double.parseDouble(input);
            } catch (NumberFormatException e) {
                isDouble = false;
            }

            if (isInt) {
                System.out.printf("%s is integer type%n", input);
            } else if (isDouble) {
                System.out.printf("%s is floating point type%n", input);
            } else if (input.length() == 1) { //this could be useless depending on your case
                System.out.printf("%s is character type%n", input);
            } else if ("true".equals(input.toLowerCase()) || "false".equals(input.toLowerCase())) {
                System.out.printf("%s is boolean type%n", input);
            } else {
                System.out.printf("%s is string type%n", input);
            }
        }
    }
}

Answer 4

class Main{
    public static void main(String args[]){
        String str;
        Scanner sc=new Scanner(System.in);
        int n,
        boolean flag=false;
        while(!flag){
            try{
                str=sc.nextLine();
                n=Integer.parseInt(str);
                flag=true;
            }
            catch(NumberFormatException e){
                System.out.println("enter an no");
                str=sc.nextLine();
            }
        }
    }
}

Answer 5

Try instanceof function with Integer instead of int.. each primitive also have a class

Answer 6

Is this ok?

class Test
{
    public static void main(String args[])
    {
        java.util.Scanner in = new java.util.Scanner(System.in);
        String x = in.nextLine();
        System.out.println("\n The type of the variable is : "+x.getClass());
    }
}

Output:

subham@subham-SVE15125CNB:~/Desktop$ javac Test.java 
subham@subham-SVE15125CNB:~/Desktop$ java Test
hello

 The type of the variable is : java.lang.String