【JavaSwing】お絵描きツールの作り方

chatGPTにJavaでのお絵描きツールの作り方を聞いてEclipseで作ってみたので、勉強のやる気を出すためにもメモ。

ArtCanvas.java

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;

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

public class ArtCanvas extends JFrame {

    private DrawArea drawArea;

    public ArtCanvas() {
        setTitle("描いて遊べるアートキャンバス 🎨");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        drawArea = new DrawArea();
        add(drawArea, BorderLayout.CENTER);

        setVisible(true);
    }

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

class DrawArea extends JPanel {

    private List<Line> lines = new ArrayList<>();
    private int prevX, prevY;
    private boolean drawing = false;

    public DrawArea() {
        setBackground(Color.WHITE);

        // マウスの動きとクリックを検知
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                prevX = e.getX();
                prevY = e.getY();
                drawing = true;
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                drawing = false;
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                if (drawing) {
                    int x = e.getX();
                    int y = e.getY();
                    lines.add(new Line(prevX, prevY, x, y));
                    prevX = x;
                    prevY = y;
                    repaint(); // 再描画
                }
            }
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 描いた線を全部描画
        g.setColor(Color.BLACK);
        for (Line line : lines) {
            g.drawLine(line.x1, line.y1, line.x2, line.y2);
        }
    }

    private static class Line {
        int x1, y1, x2, y2;

        Line(int x1, int y1, int x2, int y2) {
            this.x1 = x1;
            this.y1 = y1;
            this.x2 = x2;
            this.y2 = y2;
        }
    }
}

　　
実行すると、以下のようなウインドウが表示される。

　　
マウスで黒い線を描ける。

　　
色を選べるようにした。

ArtCanvas.java

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;

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

public class ArtCanvas extends JFrame {

    private DrawArea drawArea;

    public ArtCanvas() {
        setTitle("描いて遊べるアートキャンバス 🎨");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        drawArea = new DrawArea();
        add(drawArea, BorderLayout.CENTER);
        
        // 🎨 カラーパネルを作る
        JPanel colorPanel = new JPanel();
        colorPanel.setLayout(new FlowLayout());

        // いくつかの色ボタンを追加
        Color[] colors = {Color.BLACK, Color.RED, Color.BLUE, Color.GREEN, Color.ORANGE, Color.MAGENTA};
        for (Color c : colors) {
            JButton btn = new JButton();
            btn.setBackground(c);
            btn.setPreferredSize(new Dimension(20, 20));
            btn.addActionListener(e -> drawArea.setCurrentColor(c));
            colorPanel.add(btn);
        }

        // 「カラーピッカー」ボタン（自由に色を選ぶ）
        JButton pickerBtn = new JButton("その他の色...");
        pickerBtn.addActionListener(e -> {
            Color newColor = JColorChooser.showDialog(this, "色を選択", drawArea.getCurrentColor());
            if (newColor != null) {
                drawArea.setCurrentColor(newColor);
            }
        });
        colorPanel.add(pickerBtn);

        add(colorPanel, BorderLayout.NORTH);

        setVisible(true);
    }

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

class DrawArea extends JPanel {

    private List<Line> lines = new ArrayList<>();
    private int prevX, prevY;
    private boolean drawing = false;
    private Color currentColor = Color.BLACK;

    public DrawArea() {
        setBackground(Color.WHITE);

        // マウスの動きとクリックを検知
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                prevX = e.getX();
                prevY = e.getY();
                drawing = true;
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                drawing = false;
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                if (drawing) {
                    int x = e.getX();
                    int y = e.getY();
                    lines.add(new Line(prevX, prevY, x, y, currentColor));
                    prevX = x;
                    prevY = y;
                    repaint(); // 再描画
                }
            }
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 描いた線を全部描画
        for (Line line : lines) {
        	g.setColor(line.color);
            g.drawLine(line.x1, line.y1, line.x2, line.y2);
        }
    }
    
    public void setCurrentColor(Color c) {
    	this.currentColor = c;
    }
    
    public Color getCurrentColor() {
    	return this.currentColor;
    }
    
    private static class Line {
        int x1, y1, x2, y2;
        Color color;

        Line(int x1, int y1, int x2, int y2, Color color) {
            this.x1 = x1;
            this.y1 = y1;
            this.x2 = x2;
            this.y2 = y2;
            this.color = color;
        }
    }
}

　　
実行すると、以下のとおり。

　　
描いてみると…

　　
「その他の色」ボタンを押下すると、以下のようなカラーパレットがある。

　　
カラーパレットで選択した色で描いてみた。

　　
次は、消しゴムを追加してみた。
ChatGPTによると「白い線は実質消しゴム！」とのこと。背景が白の場合はそれでいいのかも。

ArtCanvas.java

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;

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

public class ArtCanvas extends JFrame {

    private DrawArea drawArea;
    private Color lastSelectedColor = Color.BLACK; // ← 直前の色を覚えておく

    public ArtCanvas() {
        setTitle("描いて遊べるアートキャンバス 🎨");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        drawArea = new DrawArea();
        add(drawArea, BorderLayout.CENTER);
        
        // 🎨 カラーパネル
        JPanel colorPanel = new JPanel();
        colorPanel.setLayout(new FlowLayout());

        // 色ボタン
        Color[] colors = {Color.BLACK, Color.RED, Color.BLUE, Color.GREEN, Color.ORANGE, Color.MAGENTA};
        for (Color c : colors) {
            JButton btn = new JButton();
            btn.setBackground(c);
            btn.setPreferredSize(new Dimension(20, 20));
            btn.addActionListener(e -> drawArea.setCurrentColor(c));
            colorPanel.add(btn);
        }

        // 「カラーピッカー」ボタン（自由に色を選ぶ）
        JButton pickerBtn = new JButton("その他の色...");
        pickerBtn.addActionListener(e -> {
            Color newColor = JColorChooser.showDialog(this, "色を選択", drawArea.getCurrentColor());
            if (newColor != null) {
                drawArea.setCurrentColor(newColor);
            }
        });
        colorPanel.add(pickerBtn);
        
        // 🧼 消しゴムボタン
        JButton eraserBtn = new JButton("🧽 消しゴム");
        eraserBtn.addActionListener(e -> drawArea.setCurrentColor(Color.WHITE));
        colorPanel.add(eraserBtn);
        
        // 🖌 ペンに戻るボタン
        JButton penBtn = new JButton("✏️ ペンに戻る");
        penBtn.addActionListener(e -> drawArea.setCurrentColor(lastSelectedColor));
        colorPanel.add(penBtn);

        add(colorPanel, BorderLayout.NORTH);

        setVisible(true);
    }

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

class DrawArea extends JPanel {

    private List<Line> lines = new ArrayList<>();
    private int prevX, prevY;
    private boolean drawing = false;
    private Color currentColor = Color.BLACK;

    public DrawArea() {
        setBackground(Color.WHITE);

        // マウスの動きとクリックを検知
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                prevX = e.getX();
                prevY = e.getY();
                drawing = true;
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                drawing = false;
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                if (drawing) {
                    int x = e.getX();
                    int y = e.getY();
                    lines.add(new Line(prevX, prevY, x, y, currentColor));
                    prevX = x;
                    prevY = y;
                    repaint(); // 再描画
                }
            }
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 描いた線を全部描画
        for (Line line : lines) {
        	g.setColor(line.color);
            g.drawLine(line.x1, line.y1, line.x2, line.y2);
        }
    }
    
    public void setCurrentColor(Color c) {
    	this.currentColor = c;
    }
    
    public Color getCurrentColor() {
    	return this.currentColor;
    }
    
    private static class Line {
        int x1, y1, x2, y2;
        Color color;

        Line(int x1, int y1, int x2, int y2, Color color) {
            this.x1 = x1;
            this.y1 = y1;
            this.x2 = x2;
            this.y2 = y2;
            this.color = color;
        }
    }
}

　　
こんな感じになった。

　　
「ペンに戻る」ボタンを押下すると黒いペンに。

　　
線の太さを変えられるようにしてみた。

ArtCanvas.java

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;

public class ArtCanvas extends JFrame {

    private DrawArea drawArea;
    private Color lastSelectedColor = Color.BLACK; // ← 直前の色を覚えておく

    public ArtCanvas() {
        setTitle("描いて遊べるアートキャンバス 🎨");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        drawArea = new DrawArea();
        add(drawArea, BorderLayout.CENTER);
        
        // 🎨 カラーパネル
        JPanel colorPanel = new JPanel();
        colorPanel.setLayout(new FlowLayout());

        // 色ボタン
        Color[] colors = {Color.BLACK, Color.RED, Color.BLUE, Color.GREEN, Color.ORANGE, Color.MAGENTA};
        for (Color c : colors) {
            JButton btn = new JButton();
            btn.setBackground(c);
            btn.setPreferredSize(new Dimension(20, 20));
            btn.addActionListener(e -> {
            lastSelectedColor = c;	
            drawArea.setCurrentColor(c);
        });
            colorPanel.add(btn);
        }

        // 「カラーピッカー」ボタン（自由に色を選ぶ）
        JButton pickerBtn = new JButton("その他の色...");
        pickerBtn.addActionListener(e -> {
            Color newColor = JColorChooser.showDialog(this, "色を選択", drawArea.getCurrentColor());
            if (newColor != null) {
                drawArea.setCurrentColor(newColor);
            }
        });
        colorPanel.add(pickerBtn);
        
        // 🧼 消しゴムボタン
        JButton eraserBtn = new JButton("🧽 消しゴム");
        eraserBtn.addActionListener(e -> drawArea.setCurrentColor(Color.WHITE));
        colorPanel.add(eraserBtn);
        
        // 🖌 ペンに戻るボタン
        JButton penBtn = new JButton("✏️ ペンに戻る");
        penBtn.addActionListener(e -> drawArea.setCurrentColor(lastSelectedColor));
        colorPanel.add(penBtn);

        add(colorPanel, BorderLayout.NORTH);
        
        // ✨ 線の太さスライダー
        JPanel bottomPanel = new JPanel();
        JLabel sliderLabel = new JLabel("線の太さ：");
        JSlider thicknessSlider = new JSlider(1, 50, 5); // 最小1, 最大50, 初期値5
        thicknessSlider.setMajorTickSpacing(5);
        thicknessSlider.setPaintTicks(true);
        thicknessSlider.setPaintLabels(true);

        thicknessSlider.addChangeListener(e -> {
            int value = thicknessSlider.getValue();
            drawArea.setCurrentThickness(value);
        });

        bottomPanel.add(sliderLabel);
        bottomPanel.add(thicknessSlider);

        add(bottomPanel, BorderLayout.SOUTH);

        setVisible(true);
    }

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

class DrawArea extends JPanel {

    private List<Line> lines = new ArrayList<>();
    private int prevX, prevY;
    private boolean drawing = false;
    private Color currentColor = Color.BLACK;
    private float currentThickness = 3f;

    public DrawArea() {
        setBackground(Color.WHITE);

        // マウスの動きとクリックを検知
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                prevX = e.getX();
                prevY = e.getY();
                drawing = true;
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                drawing = false;
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                if (drawing) {
                    int x = e.getX();
                    int y = e.getY();
                    lines.add(new Line(prevX, prevY, x, y, currentColor, currentThickness));
                    prevX = x;
                    prevY = y;
                    repaint(); // 再描画
                }
            }
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        // 描いた線を全部描画
        for (Line line : lines) {
        	g.setColor(line.color);
        	g2.setStroke(new BasicStroke(line.thickness, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g.drawLine(line.x1, line.y1, line.x2, line.y2);
        }
    }
    
    public void setCurrentColor(Color c) {
    	this.currentColor = c;
    }
    
    public Color getCurrentColor() {
    	return this.currentColor;
    }
    
    public void setCurrentThickness(float thickness) {
    	this.currentThickness = thickness;
    }
    
    private static class Line {
        int x1, y1, x2, y2;
        Color color;
        float thickness;

        Line(int x1, int y1, int x2, int y2, Color color, float thickness) {
            this.x1 = x1;
            this.y1 = y1;
            this.x2 = x2;
            this.y2 = y2;
            this.color = color;
            this.thickness = thickness;
        }
    }
}

　　
いろんな太さの線で描いてみた。

　
画像保存できるようにしてみた。

ArtCanvas.java

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.ArrayList;
import java.util.List;

import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;

public class ArtCanvas extends JFrame {

    private DrawArea drawArea;
    private Color lastSelectedColor = Color.BLACK; // ← 直前の色を覚えておく

    public ArtCanvas() {
        setTitle("描いて遊べるアートキャンバス 🎨");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        drawArea = new DrawArea();
        add(drawArea, BorderLayout.CENTER);
        
        // 🎨 カラーパネル
        JPanel colorPanel = new JPanel();
        colorPanel.setLayout(new FlowLayout());

        // 色ボタン
        Color[] colors = {Color.BLACK, Color.RED, Color.BLUE, Color.GREEN, Color.ORANGE, Color.MAGENTA};
        for (Color c : colors) {
            JButton btn = new JButton();
            btn.setBackground(c);
            btn.setPreferredSize(new Dimension(20, 20));
            btn.addActionListener(e -> {
            lastSelectedColor = c;	
            drawArea.setCurrentColor(c);
        });
            colorPanel.add(btn);
        }

        // 「カラーピッカー」ボタン（自由に色を選ぶ）
        JButton pickerBtn = new JButton("その他の色...");
        pickerBtn.addActionListener(e -> {
            Color newColor = JColorChooser.showDialog(this, "色を選択", drawArea.getCurrentColor());
            if (newColor != null) {
            	lastSelectedColor = newColor;
                drawArea.setCurrentColor(newColor);
            }
        }); 
        colorPanel.add(pickerBtn);
        
        // 🧼 消しゴムボタン
        JButton eraserBtn = new JButton("🧽 消しゴム");
        eraserBtn.addActionListener(e -> drawArea.setCurrentColor(Color.WHITE));
        colorPanel.add(eraserBtn);
        
        // 🖌 ペンに戻るボタン
        JButton penBtn = new JButton("✏️ ペンに戻る");
        penBtn.addActionListener(e -> drawArea.setCurrentColor(lastSelectedColor));
        colorPanel.add(penBtn);
        
        // 💾 画像保存ボタン
        JButton saveBtn = new JButton("💾 画像を保存");
        saveBtn.addActionListener(e -> drawArea.saveImage());
        colorPanel.add(saveBtn);

        add(colorPanel, BorderLayout.NORTH);
        
        // ✨ 線の太さスライダー
        JPanel bottomPanel = new JPanel();
        JLabel sliderLabel = new JLabel("線の太さ：");
        JSlider thicknessSlider = new JSlider(1, 50, 5); // 最小1, 最大50, 初期値5
        thicknessSlider.setMajorTickSpacing(5);
        thicknessSlider.setPaintTicks(true);
        thicknessSlider.setPaintLabels(true);

        thicknessSlider.addChangeListener(e -> {
            int value = thicknessSlider.getValue();
            drawArea.setCurrentThickness(value);
        });

        bottomPanel.add(sliderLabel);
        bottomPanel.add(thicknessSlider);
        add(bottomPanel, BorderLayout.SOUTH);

        setVisible(true);
    }

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

class DrawArea extends JPanel {

    private List<Line> lines = new ArrayList<>();
    private int prevX, prevY;
    private boolean drawing = false;
    private Color currentColor = Color.BLACK;
    private float currentThickness = 3f;

    public DrawArea() {
        setBackground(Color.WHITE);

        // マウスの動きとクリックを検知
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                prevX = e.getX();
                prevY = e.getY();
                drawing = true;
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                drawing = false;
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                if (drawing) {
                    int x = e.getX();
                    int y = e.getY();
                    lines.add(new Line(prevX, prevY, x, y, currentColor, currentThickness));
                    prevX = x;
                    prevY = y;
                    repaint(); // 再描画
                }
            }
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        // 描いた線を全部描画
        for (Line line : lines) {
        	g.setColor(line.color);
        	g2.setStroke(new BasicStroke(line.thickness, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g.drawLine(line.x1, line.y1, line.x2, line.y2);
        }
    }
    
    public void setCurrentColor(Color c) {
    	this.currentColor = c;
    }
    
    public Color getCurrentColor() {
    	return this.currentColor;
    }
    
    public void setCurrentThickness(float thickness) {
    	this.currentThickness = thickness;
    }
    
    // 💾 画像保存
    public void saveImage() {
        // 描画内容を BufferedImage に書き出す
        BufferedImage image = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = image.createGraphics();
        paint(g2);
        g2.dispose();

        // 保存ダイアログ
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setDialogTitle("画像を保存");
        fileChooser.setSelectedFile(new File("my_drawing.png"));
        int userSelection = fileChooser.showSaveDialog(this);

        if (userSelection == JFileChooser.APPROVE_OPTION) {
            File fileToSave = fileChooser.getSelectedFile();
            try {
                // 拡張子がない場合、自動で .png をつける
                String path = fileToSave.getAbsolutePath();
                if (!path.toLowerCase().endsWith(".png")) {
                    fileToSave = new File(path + ".png");
                }
                ImageIO.write(image, "png", fileToSave);
                JOptionPane.showMessageDialog(this, "画像を保存しました！\n" + fileToSave.getAbsolutePath());
            } catch (Exception ex) {
                JOptionPane.showMessageDialog(this, "保存に失敗しました: " + ex.getMessage());
            }
        }
    }
    
    private static class Line {
        int x1, y1, x2, y2;
        Color color;
        float thickness;

        Line(int x1, int y1, int x2, int y2, Color color, float thickness) {
            this.x1 = x1;
            this.y1 = y1;
            this.x2 = x2;
            this.y2 = y2;
            this.color = color;
            this.thickness = thickness;
        }
    }
}

　　

　　
保存できた！　やった～。

　　
塗りつぶしや画面の描画の全削除等も入れて、不要な部分を削除したりした。

ArtCanvas.java

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.LinkedList;
import java.util.Queue;

import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;

public class ArtCanvas extends JFrame {

    private DrawArea drawArea;

    public ArtCanvas() {
        setTitle("描いて遊べるアートキャンバス 🎨");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        drawArea = new DrawArea();
        add(drawArea, BorderLayout.CENTER);
        
        // 🎨 カラーパネル
        JPanel colorPanel = new JPanel();
        colorPanel.setLayout(new FlowLayout());

        // 色ボタン
        Color[] colors = {Color.BLACK, Color.RED, Color.BLUE, Color.GREEN, Color.ORANGE, Color.MAGENTA};
        for (Color c : colors) {
            JButton btn = new JButton();
            btn.setBackground(c);
            btn.setPreferredSize(new Dimension(20, 20));
            btn.addActionListener(e -> {
            drawArea.setCurrentColor(c);
        });
            colorPanel.add(btn);
        }

        // 「カラーピッカー」ボタン（自由に色を選ぶ）
        JButton pickerBtn = new JButton("その他の色...");
        pickerBtn.addActionListener(e -> {
            Color newColor = JColorChooser.showDialog(this, "色を選択", drawArea.getCurrentColor());
            if (newColor != null) {
                drawArea.setCurrentColor(newColor);
            }
        }); 
        colorPanel.add(pickerBtn);
        
        // 🖌 ペンボタン
        JButton penBtn = new JButton("ペン");
        penBtn.addActionListener(e -> drawArea.setTool("pen"));
        colorPanel.add(penBtn);
        
        // 塗りつぶし
        JButton fillBtn = new JButton("塗りつぶし");
        fillBtn.addActionListener(e -> drawArea.setTool("fill"));
        colorPanel.add(fillBtn);
        
        // 🧼 消しゴムボタン
        JButton eraserBtn = new JButton("消しゴム");
        eraserBtn.addActionListener(e -> drawArea.setCurrentColor(Color.WHITE));
        colorPanel.add(eraserBtn);
        
        // 🧭 全削除
        JButton clearBtn = new JButton("全削除");
        clearBtn.addActionListener(e -> drawArea.clearCanvas());
        colorPanel.add(clearBtn);
        
        // 💾 画像保存ボタン
        JButton saveBtn = new JButton("💾 画像を保存");
        saveBtn.addActionListener(e -> drawArea.saveImage());
        colorPanel.add(saveBtn);

        add(colorPanel, BorderLayout.NORTH);
        
        // ✨ 線の太さスライダー
        JPanel bottomPanel = new JPanel();
        JLabel sliderLabel = new JLabel("線の太さ：");
        JSlider thicknessSlider = new JSlider(1, 50, 5); // 最小1, 最大50, 初期値5
        thicknessSlider.setMajorTickSpacing(5);
        thicknessSlider.setPaintTicks(true);
        thicknessSlider.setPaintLabels(true);

        thicknessSlider.addChangeListener(e -> {
            int value = thicknessSlider.getValue();
            drawArea.setCurrentThickness(value);
        });

        bottomPanel.add(sliderLabel);
        bottomPanel.add(thicknessSlider);
        add(bottomPanel, BorderLayout.SOUTH);

        setVisible(true);
    }

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

class DrawArea extends JPanel {

    private int prevX, prevY;
    private boolean drawing = false;
    private Color currentColor = Color.BLACK;
    private float currentThickness = 3f;
    private BufferedImage canvas;
    private String currentTool = "pen"; // pen or fill

    public DrawArea() {
        setBackground(Color.WHITE);
        
        addComponentListener(new ComponentAdapter() {
            @Override
            public void componentResized(ComponentEvent e) {
                initCanvas();
            }
        });

        // マウスの動きとクリックを検知
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
            	int x = e.getX();
                int y = e.getY();
                
                if (currentTool.equals("pen")) {
                prevX = e.getX();
                prevY = e.getY();
                drawing = true;
                } else if (currentTool.equals("fill")) {
                    floodFill(x, y, canvas.getRGB(x, y), currentColor.getRGB());
                    repaint();
                }
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                drawing = false;
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                if (drawing) {
                    int x = e.getX();
                    int y = e.getY();
                 // これまでlinesに記録していたけど、canvasに直接描いてるので不要になる
                 // lines.add(new Line(prevX, prevY, x, y, currentColor, currentThickness));
                    Graphics2D g2m = canvas.createGraphics(); // canvasに直接描く
                    g2m.setColor(currentColor);
                    g2m.setStroke(new BasicStroke(currentThickness, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
                    g2m.drawLine(prevX, prevY, x, y);
                    g2m.dispose();

                    prevX = x;
                    prevY = y;
                    repaint(); // 再描画
                }
            }
        });
    }
    
    private void initCanvas() {
        int w = getWidth();
        int h = getHeight();
        if (w <= 0 || h <= 0) return;

        BufferedImage newCanvas = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2i = newCanvas.createGraphics();
        g2i.setColor(Color.WHITE);
        g2i.fillRect(0, 0, w, h);
        if (canvas != null) {
        	g2i.drawImage(canvas, 0, 0, null);
        }
        g2i.dispose();
        canvas = newCanvas;
    }

    // 🪣 Flood Fill（非再帰版）
    private void floodFill(int startX, int startY, int targetColor, int replacementColor) {
        if (targetColor == replacementColor) return;
        if (startX < 0 || startY < 0 || startX >= canvas.getWidth() || startY >= canvas.getHeight()) return;
        if (canvas.getRGB(startX, startY) != targetColor) return;

        Queue<Point> queue = new LinkedList<>();
        queue.add(new Point(startX, startY));

        while (!queue.isEmpty()) {
            Point p = queue.poll();
            int x = p.x;
            int y = p.y;

            if (x < 0 || y < 0 || x >= canvas.getWidth() || y >= canvas.getHeight()) continue;
            if (canvas.getRGB(x, y) != targetColor) continue;

            canvas.setRGB(x, y, replacementColor);

            queue.add(new Point(x + 1, y));
            queue.add(new Point(x - 1, y));
            queue.add(new Point(x, y + 1));
            queue.add(new Point(x, y - 1));
        }
    }
    
    // 🧭 全削除
    public void clearCanvas() {
        Graphics2D g2c = canvas.createGraphics();
        g2c.setColor(Color.WHITE);
        g2c.fillRect(0, 0, canvas.getWidth(), canvas.getHeight());
        g2c.dispose();
        repaint();
    }
        
    // 💾 画像保存
    public void saveImage() {
        // 描画内容を BufferedImage に書き出す
        BufferedImage image = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
        Graphics2D g2s = image.createGraphics();
        paint(g2s);
        g2s.dispose();

        // 保存ダイアログ
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setDialogTitle("画像を保存");
        fileChooser.setSelectedFile(new File("my_drawing.png"));
        int userSelection = fileChooser.showSaveDialog(this);

        if (userSelection == JFileChooser.APPROVE_OPTION) {
            File fileToSave = fileChooser.getSelectedFile();
            try {
                // 拡張子がない場合、自動で .png をつける
                String path = fileToSave.getAbsolutePath();
                if (!path.toLowerCase().endsWith(".png")) {
                    fileToSave = new File(path + ".png");
                }
                ImageIO.write(image, "png", fileToSave);
                JOptionPane.showMessageDialog(this, "画像を保存しました！\n" + fileToSave.getAbsolutePath());
            } catch (Exception ex) {
                JOptionPane.showMessageDialog(this, "保存に失敗しました: " + ex.getMessage());
            }
        }
    }
    
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
            g.drawImage(canvas, 0, 0, null);
    }
    
    public void setCurrentColor(Color c) {
    	this.currentColor = c;
    }
    
    public Color getCurrentColor() {
    	return this.currentColor;
    }
    
    public void setTool(String tool) {
        this.currentTool = tool;
    }
    
    public void setCurrentThickness(float thickness) {
    	this.currentThickness = thickness;
    }
}

　　
嬉しい！

ちょっとずつ改良したい。