Char troubles

[diggdude]

Hello, i'm pretty new to the Java programming language and it seems I have run into a brick wall with the char type.

I have written a program which translates a simple string of numbers into morse code. However, that part works perfectly, but my input validation seems to be incorrect in some way. I am constantly getting this message at compile time:

Question_1.java:22: char cannot be dereferenced
        if (input.charAt(i).isDigit() == false) {
                           ^

To put this in better context, here is the rest of the code:

import javax.swing.JOptionPane;

public class Question_1 {

    public static void main(String[] arg) {
    //Get the input
        String input = JOptionPane.showInputDialog("Enter a series of numbers: ");
        //Translate input and get rid of white space to the left and right of the string
        input = input.replaceAll("0"," -----");
        input = input.replaceAll("1"," .----");
        input = input.replaceAll("2"," ..---");
        input = input.replaceAll("3"," ...--");
        input = input.replaceAll("4"," ....-");
        input = input.replaceAll("5"," .....");
        input = input.replaceAll("6"," -....");
        input = input.replaceAll("7"," --...");
        input = input.replaceAll("8"," ---..");
        input = input.replaceAll("9"," ----.");
        input = input.trim();
        //Validation
        for (int i = 0; i <= input.length(); i++){
        if (input.charAt(i).isDigit() == false) {
                JOptionPane.showMessageDialog(null,("Non numeric   characters are not a valid input"),"Error",
                JOptionPane.INFORMATION_MESSAGE);
                break;    
            }
        }
        //Output the results
        JOptionPane.showMessageDialog(null,("The morse code is: "+input),"Morse Code",
                JOptionPane.INFORMATION_MESSAGE);
    }
}

Any help with this would be greatly appreciated, thanks in advance

Edit:

Something I forgot to add; the validation is checking for non numerical values in the string by iterating through each character, if found it will ouput an error message.

[PhHein]

if(!Character.isDigit(input.charAt(0))){

[diggdude]

if(!Character.isDigit(input.charAt(0))){

Ah, so that's how you use that method. Thank you very much, solved.