here fix

import java.util.*;

class inputStrings {

public static void main(String[ ] args) {
        Scanner userInput = new Scanner(System.in);

        List<Integer> intArray = new ArrayList<>();
        List<String> stringArray = new ArrayList<>();
        List<Double> doubleArray = new ArrayList<>();

        while(true) {
            System.out.println("Please enter a string: ");
            String text=userInput.nextLine();
            if(text.isEmpty()) {
                Collections.sort(intArray);
                Collections.sort(doubleArray);
                Collections.sort(stringArray);

                printLists(intArray.toArray());
                printLists(doubleArray.toArray());
                printLists(stringArray.toArray());
                return;
            }
           else if(isInteger(text) ){
               intArray.add(Integer.parseInt(text));
           }
            else if(isDouble(text)) {
               doubleArray.add(Double.parseDouble(text));
           }
            else {
                  stringArray.add(text);
            }
        }
    }
    public static < E > void printLists( E[] inputArray ) {
        // Display array elements
        for(E element : inputArray) {
            System.out.printf("%s ", element);
        }
        System.out.println();
    }
    public static boolean isInteger(String s) {
          boolean isValidInteger = false;
          try
          {
             Integer.parseInt(s);

             // s is a valid integer

             isValidInteger = true;
          }
          catch (NumberFormatException ex)
          {
             // s is not an integer
          }

          return isValidInteger;
    }
    public static boolean isDouble(String s) {
          boolean isValidDouble = false;
          try
          {
             Double.parseDouble(s);

             // s is a valid double

             isValidDouble = true;
          }
          catch (NumberFormatException ex)
          {
             // s is not an double
          }

          return isValidDouble;
    }
}