java - ¿Cómo pintar sobre un JPanel?

swing graphics

Question

Yo (un programador novato) estoy tratando de pintar un óvalo sobre un JPanel. Estoy tratando de usar el método pintura. Sin embargo, requiere un argumento de Gráficos. Obtengo una NullPointerException cuando incluyo mis gráficos como argumento porque es nulo, pero no sé cómo pintar el óvalo. Intenté volver a pintar, pero no pasó nada. Cualquier ayuda sería apreciada. Aquí está mi clase principal:

public class Checkers extends JPanel{
 public static final int BOARDSQUARES = 8;
 public static final int BOARDSIZE = 75;
   private JPanel[][] board;
   private final Point point1;
   private final LineBorder border1;
   public JFrame frame;
   checkerPiece piece = new checkerPiece(this);
   Graphics g;

public Checkers(){
    board = new JPanel[BOARDSQUARES][BOARDSQUARES];
    point1 = new Point (BOARDSIZE,BOARDSIZE);
    border1=new LineBorder(Color.BLACK, 1);

}


/**
 * @param args the command line arguments
 */
public static void main(String[] args) {

     Checkers checkers = new Checkers();
   checkers.frame=checkers.createJFrame();

   checkers.board =checkers.createBoard(checkers.board, checkers.point1, checkers.border1);

  for (int y=0;y<BOARDSQUARES;y++){
      for (int x = 0;x<BOARDSQUARES;x++){
      checkers.frame.getContentPane().add(checkers.board[y][x]);

        }

  }

    checkers.paint(checkers.g);
}

private JPanel[][] createBoard (JPanel[][] board, Point point, LineBorder border1){
    for (int row = 0; row<BOARDSQUARES;row++){
        point.y=BOARDSIZE;
        for (int col = 0; col <BOARDSQUARES;col++){

            board[row][col] = new JPanel();
            board[row][col].setLocation(point);
            board[row][col].setVisible(true);
            board[row][col].setSize(BOARDSIZE,BOARDSIZE);
            board[row][col].setOpaque(true);
             if ((row%2==0&&col%2==0)||(row%2==1&&col%2==1)){
                board[row][col].setBackground(new Color (230,200,150));
            } else if ((row%2==0&&col%2==1)||(row%2==1&&col%2==0)) {

                 board[row][col].setBackground(new Color (165, 42,42) );
             }
             board[row][col].setBorder(border1);
                             point.y = point.y+BOARDSIZE;
        }
        point.x=point.x+BOARDSIZE;
    }

    return board;
}

private JFrame createJFrame (){
    JFrame mainFrame = new JFrame("Checkers");
    mainFrame.setSize(1000,1000);
    mainFrame.setVisible(true);
    mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  mainFrame.add(new Checkers());
return mainFrame;
}
 @Override
public void paint (Graphics g){
    System.out.println("hi");
    super.paint(g);
    Graphics2D g2d = (Graphics2D) g;

    piece.paint(g2d,board[0][0].getLocation().x,board[0][0].getLocation().y,Color.BLACK);

   }
}

Un fragmento necesario de mi otra clase (pieza cherkerPiece):

public void paint (Graphics2D g, int x, int y, Color color){
    g.setColor(color);
    g.fillOval(x, y, DIAMETER, DIAMETER);
}

Gracias por tu ayuda

Answer 1

Para crear algo tan complejo como un juego de damas, debe seguir el patrón de modelo / vista / controlador al crear su GUI de Java Swing.

Creé una clase de modelo para un cuadrado de tablero de damas y otra clase de modelo para una pieza de damas. Creé una clase de modelo para el tablero de damas y otra clase de modelo para albergar todas las fichas de damas.

Creé una clase de vista para dibujar el tablero de ajedrez. Creé otra clase de vista para crear la ventana principal.

No creé ninguna clase de controlador. Este código simplemente te muestra cómo dibujar un tablero de damas. Puse todas las clases juntas para que sea más fácil pegar el código. Debe separar las clases en archivos separados de Java.

package com.ggl.testing;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class CheckerBoard implements Runnable {

    private Board board;

    private CheckerBoardPanel checkerBoardPanel;

    private JFrame frame;

    private Pieces pieces;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new CheckerBoard());
    }

    public CheckerBoard() {
        this.board = new Board();
        this.pieces = new Pieces();
    }

    @Override
    public void run() {
        frame = new JFrame("Checker Board");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        checkerBoardPanel = new CheckerBoardPanel(board, pieces);
        frame.add(checkerBoardPanel);

        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public class CheckerBoardPanel extends JPanel {

        private static final long serialVersionUID = 3770663347384271771L;

        private Board board;

        private Pieces pieces;

        public CheckerBoardPanel(Board board, Pieces pieces) {
            this.board = board;
            this.pieces = pieces;
            this.setPreferredSize(board.getPreferredSize());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Square[][] checkerBoard = board.getBoard();

            for (int row = 0; row < checkerBoard.length; row++) {
                for (int column = 0; column < checkerBoard[row].length; column++) {
                    Square square = checkerBoard[row][column];
                    Rectangle drawingRectangle = square.getDrawingRectangle();
                    g.setColor(square.getColor());
                    g.fillRect(drawingRectangle.x, drawingRectangle.y,
                            drawingRectangle.width, drawingRectangle.height);
                }
            }

            List<Piece> checkerPieces = pieces.getPieces();

            for (Piece checkerPiece : checkerPieces) {
                Point coordinate = checkerPiece.getCoordinate();
                Rectangle drawingRectangle = checkerBoard[coordinate.x][coordinate.y]
                        .getDrawingRectangle();

                int x = drawingRectangle.x + drawingRectangle.width / 2;
                int y = drawingRectangle.y + drawingRectangle.height / 2;
                int radius = board.getSquareWidth() * 2 / 6;

                g.setColor(checkerPiece.getColor());
                g.fillOval(x - radius, y - radius, radius + radius, radius
                        + radius);
            }
        }
    }

    public class Board {

        private static final int BOARD_WIDTH = 8;
        private static final int SQUARE_WIDTH = 64;

        private Square[][] board;

        public Board() {
            this.board = initalizeBoard(BOARD_WIDTH, SQUARE_WIDTH);
        }

        private Square[][] initalizeBoard(int boardWidth, int squareWidth) {
            Square[][] board = new Square[boardWidth][boardWidth];

            int x = 0;
            int y = 0;

            for (int row = 0; row < boardWidth; row++) {
                for (int column = 0; column < boardWidth; column++) {
                    Square square = new Square();
                    if (isLightSquare(row, column)) {
                        square.setColor(Color.WHITE);
                    } else {
                        square.setColor(Color.LIGHT_GRAY);
                    }

                    square.setCoordinate(new Point(row, column));
                    square.setDrawingRectangle(new Rectangle(x, y, squareWidth,
                            squareWidth));

                    board[row][column] = square;

                    x += squareWidth;
                }
                x = 0;
                y += squareWidth;
            }

            return board;
        }

        public boolean isLightSquare(int row, int column) {
            if (row % 2 == 0) {
                if (column % 2 == 0) {
                    return true;
                } else {
                    return false;
                }
            } else {
                if (column % 2 == 0) {
                    return false;
                } else {
                    return true;
                }
            }
        }

        public Dimension getPreferredSize() {
            int width = SQUARE_WIDTH * 8 + 1;
            return new Dimension(width, width);
        }

        public Square[][] getBoard() {
            return board;
        }

        public int getSquareWidth() {
            return SQUARE_WIDTH;
        }

    }

    public class Square {

        private Color color;

        private Point coordinate;

        private Rectangle drawingRectangle;

        public Point getCoordinate() {
            return coordinate;
        }

        public void setCoordinate(Point coordinate) {
            this.coordinate = coordinate;
        }

        public Rectangle getDrawingRectangle() {
            return drawingRectangle;
        }

        public void setDrawingRectangle(Rectangle drawingRectangle) {
            this.drawingRectangle = drawingRectangle;
        }

        public Color getColor() {
            return color;
        }

        public void setColor(Color color) {
            this.color = color;
        }

    }

    public class Pieces {

        private List<Piece> pieces;

        public Pieces() {
            this.pieces = addPieces();
        }

        private List<Piece> addPieces() {
            List<Piece> pieces = new ArrayList<Piece>();

            Piece piece = new Piece();
            piece.setColor(Color.RED);
            piece.setCoordinate(new Point(2, 1));
            pieces.add(piece);

            piece = new Piece();
            piece.setColor(Color.BLACK);
            piece.setCoordinate(new Point(5, 0));
            pieces.add(piece);

            // Add the rest of the red and black pieces here

            return pieces;
        }

        public List<Piece> getPieces() {
            return pieces;
        }

        public void addPiece(Piece piece) {
            this.pieces.add(piece);
        }
    }

    public class Piece {

        private Color color;

        private Point coordinate;

        public Color getColor() {
            return color;
        }

        public void setColor(Color color) {
            this.color = color;
        }

        public Point getCoordinate() {
            return coordinate;
        }

        public void setCoordinate(Point coordinate) {
            this.coordinate = coordinate;
        }

    }

}

Answer 2

necesita agregar una clase que extienda Canvas y que haga toda su pintura en esa clase. Me gusta esto

public class FirstWindow extends JFrame
{
/**
 * 
 */
    private static final long serialVersionUID = 1L;

public FirstWindow()
{
    super("Kayte does not go to water parks");
    setSize(500, 500);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setResizable(false);
}
}

public class Start extends Canvas implements Runnable

public class Main
{

public static void main(String arg[])
{
    FirstWindow fw = new FirstWindow();

    Start game = new Start(500, 500);
    fw.add(game);
    fw.setVisible(true);
    new Thread(game).start();
}

}