Showing user input in a JFrame

Question

i need to be able to take user-given values and display them in a JFrame. i'm testing the input of a sudoku puzzle. i have a sudokuComponent and a sudokuViewer.
i'm confused as to where to place my code that will do the process of taking user input (via Scanner class) and testing it for certain conditions.
i dont think figuring out the testing conditions should be hard, i'm just having trouble with getting the input read in correctly and a way of getting it displayed on the JFrame which displays the sudoku puzzle with the values so far.
i was given a tip that said i needed to use the method repaint() of JFrame to see the updates.
SUDOKUCOMPONENT
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.Line2D;
import javax.swing.JPanel;
import javax.swing.JComponent;
import java.util.Scanner;
public class SudokuComponent extends JComponent
     public void paintComponent(Graphics g)
          //recover graphics2s
          Graphics2D g2 = (Graphics2D) g;
          //Construct the Sudoku square
          Rectangle box = new Rectangle(20, 20, 270, 270);
          g2.draw(box);
          g2.draw(new Line2D.Double(20, 110, 290, 110)); //horizontal
          g2.draw(new Line2D.Double(20, 200, 290, 200));
          g2.draw(new Line2D.Double(110, 20, 110, 290)); //vertical
          g2.draw(new Line2D.Double(200, 20, 200, 290));
}SUDOKUVIEWER
import javax.swing.JFrame;
import java.util.Scanner;
public class SudokuViewer
   public static void main(String[] args)
      JFrame frame = new JFrame();
      final int FRAME_WIDTH = 350;
      final int FRAME_HEIGHT = 350;
      frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
      frame.setTitle("Sudoku Viewer");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      SudokuComponent component = new SudokuComponent();
      frame.add(component);
      frame.setVisible(true);
}

Answer 1

I have improved your application to show how it can be programmed.
For more information you can see about
KeyListener:
http://java.sun.com/docs/books/tutorial/uiswing/events/keylistener.html
MouseListener:
http://java.sun.com/docs/books/tutorial/uiswing/events/mouselistener.html
and of course use repaint() when you want to update your component
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.util.LinkedList;
import java.util.List;
import javax.swing.JComponent;
public class SudokuComponent extends JComponent {
    SudokuElement currentElement = new SudokuElement();
    List<SudokuElement> elementList = new LinkedList<SudokuElement>();
    public SudokuComponent(){
        addMouseListener(new MyMouseListener());
        setFocusable(true);
        addKeyListener(new MyKeyListener());
    public void paintComponent(Graphics g) {
        //public void paint(Graphics g) {
        //recover graphics2s
        Graphics2D g2 = (Graphics2D) g;
        //Construct the Sudoku square
        Rectangle box = new Rectangle(20, 20, 270, 270);
        g2.draw(box);
        g2.draw(new Line2D.Double(20, 110, 290, 110)); //horizontal
        g2.draw(new Line2D.Double(20, 200, 290, 200));
        g2.draw(new Line2D.Double(110, 20, 110, 290)); //vertical
        g2.draw(new Line2D.Double(200, 20, 200, 290));
        // show place where user can type a digit
        g2.draw(new Line2D.Double(currentElement.x - 10, currentElement.y, currentElement.x + 10, currentElement.y));
        // show all typed digits
        for(SudokuElement elem : elementList ){
           g2.drawString(elem.digit + "", elem.x, elem.y);
    class SudokuElement {
        int digit;
        int x;
        int y;
        SudokuElement getCopy(){
            SudokuElement elem = new SudokuElement();
            elem.x = x;
            elem.y = y;
            elem.digit= digit;
            return elem;
    class MyMouseListener extends MouseAdapter {
        public void mouseClicked(MouseEvent e) {
            System.out.println("mouse clicked: x = "  + e.getX() + " y = " + e.getY());
            currentElement.x = e.getX();  // It is better to use local coordinats 0 .. 9
            currentElement.y = e.getY();
            repaint(); 
    class MyKeyListener extends KeyAdapter {
        public void keyTyped(KeyEvent e) {
            char ch = e.getKeyChar();
            System.out.println("char typed= " + ch);
            if( Character.isDigit(ch) ){  // Filter only digits
                currentElement.digit = Character.digit(ch, 10);
                elementList.add(currentElement.getCopy());
                repaint();
}