Read last char of a String

Question

I have the following code that functions like a basic RPN calculator:
public class Main {
     * @param args the command line arguments
     static public ArrayList<Double> stack = new ArrayList<Double>();
     static double numberInput;
     static double answer;
     static String operation;
//Prints Welcome screen, initialized checkforInput
     public static void main(String[] args) {
         System.out.println();
         System.out.println("Welcome to RPNCalc by theCoffeeShop()");
         checkForInput();
//Checks for input, redirects to appropriate method
     public static void checkForInput() {
         Scanner reader = new Scanner(System.in);
      String input = reader.nextLine();
         if(isDouble(input) == true) {
            double number = Double.parseDouble( input );
            stack.add(0, number);
            repeat();
         } else {
            operation = input;
            operation();
//Processes numeric operations
     public static void operation () {
         if(operation.equals("+")) {
             answer = stack.get(1)+stack.get(0);
             stack.add(0, answer);
             System.out.println(answer);
             repeat();
         } else if (operation.equals("-")) {
             answer = stack.get(1)-stack.get(0);
             stack.add(0, answer);
             System.out.println(answer);
             repeat();
         } else if (operation.equals("*")) {
             answer = stack.get(1)*stack.get(0);
             stack.add(0, answer);
             System.out.println(answer);
             repeat();
         } else if (operation.equals("/")) {
             answer = stack.get(1)/stack.get(0);
             stack.add(0, answer);
             System.out.println(answer);
             repeat();
         } else {
             System.out.println("Incompatible operation");
             repeat();
//Called when ready to recheck for input
     public static void repeat() {
         checkForInput();
//Checks if string is double
     public static boolean isDouble( String input )
        try
            Double.parseDouble( input );
            return true;
        catch(Exception e)
           return false;
}To perform a basic operation (5+2), you would do the following
5
enter
2
enter
(plus)
enter
Computer prints 7.
I would like it to function like this:
5
enter
2(plus)
enter
Computer prints 7.
To do this, I have to be a be to split a string into 2 parts, the operation and the number. I think I could do this with a StringBuffer, but How to read the LAST char of a StringBuffer, instead of just a specific char? If there is a way to do it w/out a StringBuffer, I'm open to suggestions.

Answer 1

Hint:
The last character of a String (or StringBuilder or StringBuffer, etc.) is at the index (length_of_string - 1).
Are you sure you're supposed to solve the problem this way? Usually homework assignments of this sort involve writing a whole parser.