Finding Data Type of User Input using Regular Expression in Java

Given a string, the task is to find its corresponding datatype using regular expression in java.

We can broadly classify all data types into following types:

1. Integer: Numeric datatypes like byte, short, int, long take the form of an Integer object.
2. Double: Decimal datatypes like float and double take the form of Double object.
3. Date: Date in any format (like dd-mm-yyyy or dd/mm/yyyy) is a part of java.util.Date
4. String: All remaining inputs come under the String type.

Note: Character inputs and boolean values will also be considered as string.

Examples:

Input: “56.73”

Output: java.lang.Double

Explanation: 56.73 is of float data type which are part of java.lang.Double

Input: “true”

Output: java.lang.String

Explanation: Here true is considered as a regular string which is a part of java.lang.String

Approach:

• Take input in the form of a string.
• Now if the input contains only digits, it is an Integer object. If it contains numbers with a decimal point, it is a Double-object. If the input is in the form of a Date, we print it as java.util.Date object. Else, we say that the input is a String object which may contain alphanumeric and special characters.

Below is the implementation of the above approach:

Java

public class GFG {

    // method stub
    public static void main(String[] arg)
    {

        String input = "56.73";
        String dataType = null;

        // checking for Integer
        if (input.matches("\\d+")) {
            dataType = "java.lang.Integer";
        }

        // checking for floating point numbers
        else if (input.matches("\\d*[.]\\d+")) {
            dataType = "java.lang.Double";
        }

        // checking for date format dd/mm/yyyy
        else if (input.matches(
                     "\\d{2}[/]\\d{2}[/]\\d{4}")) {
            dataType = "java.util.Date";
        }

        // checking for date format mm/dd/yyyy
        else if (input.matches(
                     "\\d{2}[/]\\d{2}[/]\\d{4}")) {
            dataType = "java.util.Date";
        }

        // checking for date format dd-mon-yy
        else if (input.matches(
                     "\\d{2}[-]\\w{3}[-]\\d{2}")) {
            dataType = "java.util.Date";
        }

        // checking for date format dd-mon-yyyy
        else if (input.matches(
                     "\\d{2}[-]\\w{3}[-]\\d{4}")) {
            dataType = "java.util.Date";
        }

        // checking for date format dd-month-yy
        else if (input.matches("\\d{2}[-]\\w+[-]\\d{2}")) {
            dataType = "java.util.Date";
        }

        // checking for date format dd-month-yyyy
        else if (input.matches("\\d{2}[-]\\w+[-]\\d{4}")) {
            dataType = "java.util.Date";
        }

        // checking for date format yyyy-mm-dd
        else if (input.matches(
                     "\\d{4}[-]\\d{2}[-]\\d{2}")) {
            dataType = "java.util.Date";
        }

        // checking for String
        else {
            dataType = "java.lang.String";
        }

        System.out.println("The datatype of " + input
                           + " is: " + dataType);
    }
}

Output

The datatype of 56.73 is: java.lang.Double