Character input help!!!!

[Dio1080]

I need to this program to let me enter in an letters A B C or D so this program can run, why isn't this program not working, please help.
Here is my code:

public class DriversLicense{
    public static void main(String [] args) {
   //Students answers to the questions
   char [][] answers = new char [0][20];
    String input = javax.swing.JOptionPane.showInputDialog("Enter char: ");
    char input2 = input.charAt(0);
    answers[0][20] = input2;


   //key to the questions
    char[] keys = {'B', 'D', 'A', 'A', 'C', 'A', 'B', 'A', 'C', 'D', 'B', 'C', 'D', 'A', 'D', 'C', 'C', 'B', 'D', 'A'}; 
    //Grade all answers
   for (int i = 0; i < answers.length; i++) {
    //Grade one student
    int correctCount = 0;

    for(int j = 0; j < answers[i].length; j++){
    if (answers[i][j] == keys[j])
    correctCount++;
    }

    System.out.println("Student " + i + "'s correct count is " + correctCount);
    System.out.print("   "  + answers[0][20]);
    }
    }
    }