为什么某些涉及字符串的方法会阻止 paintComponent() 工作？

Question

我正在研究二十一点项目。它可以工作，但在向其添加投注功能时，三件事导致程序被绘制为空白的白色面板： 1. 如果我有一个 JLabel。 2. 如果我有一个 JTextField，构造函数中的 String 参数不为 null。 3. 如果我在面板的构造函数中有一个 drawString() 调用，其中包含一个从双精度转换为字符串的字符串参数。

这是整个程序，问题区域已用注释标记：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class BlackjackGUI extends JPanel implements ActionListener{

    private static Deck deck;
    private static BlackjackHand userHand = new BlackjackHand();
    private static BlackjackHand dealerHand = new BlackjackHand();
    private static String message = "Play Blackjack!";
    private static JButton hit, stand;
    private static JTextField betField;
    private static double pot = 100.0;

    public static void main(String[] args){

        JFrame window = new JFrame("Blackjack");
        window.setVisible(true);
        window.setSize(600, 450);
        window.setResizable(false);
        BlackjackGUI content = new BlackjackGUI();
        window.setContentPane(content);

    }

    public BlackjackGUI(){//constructs button panel and panel with cards.

        setLayout(new BorderLayout());

        JPanel cardTable = new JPanel();
        setOpaque(true);
        setBackground(new Color(164, 0, 45));
        cardTable.setOpaque(false);
        add(cardTable, BorderLayout.CENTER);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setBorder(BorderFactory.createEtchedBorder());

        hit = new JButton("Hit");
        hit.addActionListener(this);
        hit.setEnabled(false);
        buttonPanel.add(hit);

        stand = new JButton("Stand");
        stand.addActionListener(this);
        stand.setEnabled(false);
        buttonPanel.add(stand);

        JButton newGame = new JButton("New Game");
        newGame.addActionListener(this);
        buttonPanel.add(newGame);

        JLabel betLabel = new JLabel("Bet:");//This is a problem.
        buttonPanel.add(betLabel);

        betField = new JTextField("0", 5);//Also a problem.
        buttonPanel.add(betField);

        add(buttonPanel, BorderLayout.SOUTH);

    }

    public void paintComponent(Graphics g){

        super.paintComponent(g);
        int i;//iterator

        for(i = 0; i < dealerHand.getCardCount(); i ++){

            if(i == 1)
                drawCard(g, dealerHand.getCard(i), 10 + (100 * i), 60, true);
            else
                drawCard(g, dealerHand.getCard(i), 10 + (100 * i), 60, false);

        }
        for(i = 0; i < userHand.getCardCount(); i ++){
            drawCard(g, userHand.getCard(i), 10 + (100 * i), 220, true);
        }

        g.setColor(Color.BLUE);
        g.drawString(message, 10, 370);
        g.drawString("Dealer's Cards:", 10, 50);
        g.drawString("Your Cards:", 10, 210);
        g.drawString(String.valueOf(pot), 300, 210);//Also a problem.

    }

    public void actionPerformed(ActionEvent evt){

        String button = evt.getActionCommand();
        if(button.equals("New Game")){

            deck = new Deck(false);
            userHand = new BlackjackHand();
            dealerHand = new BlackjackHand();
            deck.shuffle();
            userHand.addCard(deck.dealCard());
            userHand.addCard(deck.dealCard());
            dealerHand.addCard(deck.dealCard());
            dealerHand.addCard(deck.dealCard());

            handAssessment(userHand.getBlackjackValue(), dealerHand.getBlackjackValue());

            repaint();

        }
        else if(button.equals("Hit")){

            userHand.addCard(deck.dealCard());
            handAssessment(userHand.getBlackjackValue(), dealerHand.getBlackjackValue());
            repaint();

        }
        else if(button.equals("Stand")){
            if(dealerHand.getBlackjackValue() < 17)
                dealerHand.addCard(deck.dealCard());

            if(userHand.getBlackjackValue() > dealerHand.getBlackjackValue())
                message = "You win!";
            else
                message = "You lose.";

            hit.setEnabled(false);
            stand.setEnabled(false);
            repaint();
        }

    }

    /**
     * Draws a card as a 80 by 100 rectangle with upper left corner at (x,y).
     * The card is drawn in the graphics context g.  If card is null, then
     * a face-down card is drawn.  (The cards are rather primitive!)
     */
    void drawCard(Graphics g, Card card, int x, int y, boolean faceUp) {
        if (!faceUp) {  
            // Draw a face-down card
            g.setColor(Color.BLUE);
            g.fillRect(x,y,80,100);
            g.setColor(Color.WHITE);
            g.drawRect(x+3,y+3,73,93);
            g.drawRect(x+4,y+4,71,91);
        }
        else {
            g.setColor(Color.WHITE);
            g.fillRect(x,y,80,100);
            g.setColor(Color.GRAY);
            g.drawRect(x,y,79,99);
            g.drawRect(x+1,y+1,77,97);
            if (card.getSuit() == Card.DIAMONDS || card.getSuit() == Card.HEARTS)
                g.setColor(Color.RED);
            else
                g.setColor(Color.BLACK);
            g.drawString(card.getValueAsString(), x + 10, y + 30);
            g.drawString("of", x+ 10, y + 50);
            g.drawString(card.getSuitAsString(), x + 10, y + 70);
        }
    } // end drawCard()

    /**
        Assesses whether the game is over or not based on the values of each player's hand. Determines functionality of buttons accordingly.
        @param userVal The blackjack value of the player's hand.
        @param dealerVal The blackjack value of the dealer's hand.
    */
    void handAssessment(int userVal, int dealerVal){

        //dealer has 21
        if(dealerVal == 21){

            message = "You lose. Dealer has 21.";
            hit.setEnabled(false);
            stand.setEnabled(false);

        }
        //player has 21
        else if(userVal == 21){

            message = "You win with 21!";
            hit.setEnabled(false);
            stand.setEnabled(false);

        }
        //player is over 21
        else if(userVal > 21){

            message = "You lose. You went over 21.";
            hit.setEnabled(false);
            stand.setEnabled(false);

        }
        //dealer is over 21
        else if(dealerVal > 21){

            message = "You win! Dealer is over 21!";
            hit.setEnabled(false);
            stand.setEnabled(false);

        }
        //player has more than dealer
        else{

            message = "Hit or Stand?";
            hit.setEnabled(true);
            stand.setEnabled(true);

        }

    }

}

我猜这个问题与 paintComponent() 的工作方式有关。有什么想法吗？

Answer 1

"Call setVisible only AFTER you have established the basic UI." - 美食节目

为什么某些涉及字符串的方法会阻止 paintComponent() 工作？

Why do certain methods involving strings prevent paintComponent() from working?

java

string

graphics

paintcomponent