无论我做什么，JLabel都不会露面

Question

我尝试了很多不同的东西试图让JLabel展示，但我不明白为什么它不起作用。我已经尝试过调整它，虽然这不是我想要做的，但我尝试过其他课程，但我更愿意坚持使用这一课程，并且它开始变得非常令人沮丧。如果您有任何想法，请帮忙。但是请尽量保持简单并且非常清楚地解释，因为我对java仍然很新。我只走了三四个月。这是我的代码：

package com.thefallenpaladin;

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

/**
 * Created by darkp_000 on 11/4/2015.
 */
@SuppressWarnings("serial")
public class Game extends JPanel implements KeyListener,MouseListener {

    public boolean mainMenu = true;

    public int winWidth = 700;  //Window Stats
    public int winHeight = 600;

    public int buttonOneX = 60; // Button Stats
    public int buttonOneY = 240;
    public int buttonOneW = 100;
    public int buttonOneH = 75;
    public boolean buttonOne = false;

    public int mouseX; // not set because it is set in mouseClicked
    public int mouseY;

    public static void main(String[] args) {
        Game game = new Game();

        JFrame window = new JFrame("I hate this");
        JLabel onePlayer = new JLabel();
        onePlayer.setLocation(0,0/*game.buttonOneX +         game.buttonOneX/2,game.buttonOneY + game.buttonOneY/2*/);
        window.add(game);

        window.setFocusable(true);
        window.setResizable(false);
        window.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        window.setSize(700,600); //TODO
        window.setVisible(true);

        game.requestFocusInWindow();
        game.add(onePlayer);
        game.addKeyListener(game);
        game.addMouseListener(game);


        window.setLocationRelativeTo(null);

        while(true) { // Main Game loop
            onePlayer.setText("One Player");
            game.repaint();
            game.customUpdate();
        } 
    }

    public void customUpdate() {
        if(mouseX > buttonOneX && mouseX < buttonOneX+buttonOneX && mouseY >     buttonOneY && mouseY < buttonOneY+buttonOneY && mainMenu) {
            buttonOne = true;
            System.out.print("Starting Game");
        }
    }

    public void paint(Graphics g) {
        if(mainMenu) {
            g.setColor(Color.CYAN); // Set main menu
            g.fillRect(0,0,winWidth,winHeight);
            g.setColor(Color.GREEN);
            g.fillRect(buttonOneX,buttonOneY,buttonOneW,buttonOneH);
        }
        if(buttonOne) {
            mainMenu = false;
            g.setColor(Color.GREEN);
            g.fillRect(0,0,winWidth,winHeight);
        }
    }

    public void keyTyped(KeyEvent e) {

    }

    public void keyPressed(KeyEvent e) {
        System.out.println(e);
    }

    public void keyReleased(KeyEvent e) {

    }

    public void mouseClicked(MouseEvent e) {

    }

    public void mousePressed(MouseEvent e) {
//        System.out.println(e);
        mouseX = e.getX();
        mouseY = e.getY();

}

    public void mouseReleased(MouseEvent e) {

    }

    public void mouseEntered(MouseEvent e) {

    }

    public void mouseExited(MouseEvent e) {

    }
    }

Answer 1

好的，所以你犯了几个基本的错误......

首先，JLabel onePlayer = new JLabel();创建一个没有大小（0x0）的空标签，因为标签默认是透明的，所以你看不到它

接下来，您已覆盖顶级容器（paint）的JFrame，但未能有效地保护绘制链，以防止任何子组件被绘制

public void paint(Graphics g) {
    if (mainMenu) {
        g.setColor(Color.CYAN); // Set main menu
        g.fillRect(0, 0, winWidth, winHeight);
        g.setColor(Color.GREEN);
        g.fillRect(buttonOneX, buttonOneY, buttonOneW, buttonOneH);
    }
    if (buttonOne) {
        mainMenu = false;
        g.setColor(Color.GREEN);
        g.fillRect(0, 0, winWidth, winHeight);
    }
}

因此，如果我删除了您的绘画方法并将JLabel onePlayer = new JLabel();更改为JLabel onePlayer = new JLabel("I'm a label");，我会收到此输出...

也...

while (true) { // Main Game loop
    onePlayer.setText("One Player");
    game.repaint();
    game.customUpdate();
}

有可能试图搞砸你的程序，你无法保证在你的main方法被调用的线程中，你不应该做出假设。

首先创建一个自定义组件，从JPanel扩展并覆盖它的paintComponent方法，然后将自定义绘画放在那里。实际上，您应该为游戏的每个状态（菜单，运行，设置等）设置一个面板。

将这些添加到您的框架中（可能使用CardLayout，以便您可以轻松地在它们之间切换）

使用Thread或Swing Timer作为主游戏循环，您可以明确创建。

查看Painting in AWT and Swing，Performing Custom Painting，How to Use CardLayout和How to use Swing Timers了解更多详情

作为＆＃34;概念＆＃34;示例...

import java.awt.CardLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class AwesomeGame {

    public static void main(String[] args) {
        new AwesomeGame();
    }

    public AwesomeGame() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new ContentPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public interface NavigationController {
        public void letsPlay();
    }

    public class ContentPane extends JPanel implements NavigationController {

        private CardLayout cardLayout;
        private GamePane gamePane;

        public ContentPane() {
            cardLayout = new CardLayout();
            setLayout(cardLayout);
            add(new MenuPane(this), "TheMenu");
            add((gamePane = new GamePane()), "TheGame");
            cardLayout.show(this, "TheMenu");
        }

        @Override
        public void letsPlay() {
            cardLayout.show(this, "TheGame");
            gamePane.play();
        }

    }

    public class MenuPane extends JPanel {

        public MenuPane(NavigationController navigationController) {
            JLabel label = new JLabel("My Super Dupa Awesome Game!");
            label.setFont(label.getFont().deriveFont(Font.BOLD, 48));
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            add(label, gbc);

            JButton play = new JButton("Play Now!");
            play.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    navigationController.letsPlay();
                }
            });
            add(play, gbc);

            setBackground(Color.GREEN);
        }

    }


    public class GamePane extends JPanel {

        public GamePane() {
            setBackground(Color.BLUE);
        }

        public void play() {
            Timer timer = new Timer(500, new ActionListener() {
                int count;
                @Override
                public void actionPerformed(ActionEvent e) {
                    count++;
                    if (count % 2 == 0) {
                        setForeground(Color.BLACK);
                    } else {
                        setForeground(Color.RED);
                    }
                    repaint();
                }
            });
            timer.start();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            String text = "I bet you're blowen away by it's awesomness!";
            FontMetrics fm = g2d.getFontMetrics();
            int x = (getWidth() - fm.stringWidth(text)) / 2;
            int y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();
            g2d.drawString(text, x, y);
            g2d.dispose();
        }

    }
}