how to check primitive data type of any value in java

Question

I have a file containing list of values which may be just a string or an integer.

bhushan 21
kedar 20

When i read values in a string array i also want to perform some arithmetic operations if the data that i have is an integer or double. How do i check whether the data that i have is an integer, double or a string? I am currently storing all values in a string array using split function and whenever i want to take average of all numbers i convert the numbers that i am sure of to integers or double and then perform arithmetic operations. I want to write a method that will tell me what exactly is the type of that value.

Answer 1

Using a regular expression should be the most efficient way. Other expressions can be used to further look for floating point numbers, etc.

String input = "12345";
java.util.regex.Pattern pattern = java.util.regex.Pattern.compile(".*[^0-9].*");

if( pattern.matcher(input).matches() )
    System.out.println("Its a number");
else
    System.out.println("Its not a number");

You can also use the Integer.parseInt() or Double.parseDouble() methods, however, they will throw a NumberFormatException if the input does not conform.

Answer 2

You can do that with simple function;

public static boolean isValueInteger(String s) {
    try { 
        Integer.parseInt(s); 
    } catch(NumberFormatException e) { 
        return false;//For example "bhushan" 
    }
    return true;// For example "21" 
}

It will throw NumberFormatException if it is a String

Answer 3

You can try to cast it from string to int.

try{
  int result = Integer.parseInt(stringValue);
} catch (NumberFormatException nfe) {
}

Answer 4

You usually would use something like regular expression for that. eg

String number = "daaaa";
Pattern digitPattern = Pattern.compile("\\d{6}");       

if (digitPattern.matcher(number).matches()) {
   System.out.println(number + " is a number.");
}