为什么我不能在 java 15 中使用自定义 jcomponent 来使用 createImage？

Question

为什么这不起作用以及为什么 function createImage来自Component class 而不是来自JComponent class？ 无法理解。

我的jComponent ：

package net.danielgolan.paint.graphics;

import org.jetbrains.annotations.NotNull;

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

public class DrawingArea extends JComponent implements MouseMotionListener {
    private Image image;
    private Graphics2D graphics2D;
    private int mouseX, mouseY, currentMouseX, currentMouseY;
    private @NotNull DrawingArea.Mode drawingMode;
    private @NotNull Color backgroundColor = Color.WHITE, foregroundColor = Color.BLACK;

    public DrawingArea(@NotNull DrawingArea.Mode drawingMode){
        this.drawingMode = drawingMode;

        resetImage();

        setDoubleBuffered(false);

        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                mouseX = e.getX();
                mouseY = e.getY();
            }
        });

        addMouseMotionListener(this);
    }

    public @NotNull Graphics2D getGraphics2D() {
        return graphics2D;
    }

    public @NotNull DrawingArea.Mode getDrawingMode() {
        return drawingMode;
    }

    public void setDrawingMode(@NotNull DrawingArea.Mode drawingMode) {
        this.drawingMode = drawingMode;
    }

    public Image getImage() {
        return image;
    }

    @Override
    protected void paintComponent(Graphics g) {
        if (image == null) resetImage();

        g.drawImage(image, 0, 0, null);
    }

    protected void resetImage(){
        image = createImage(getSize().width, getSize().height);
        graphics2D = (Graphics2D) image.getGraphics();

        enableAntialiasing();
        clear();
    }

    protected final void enableAntialiasing() {
        graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    }

    public void clear() {
        graphics2D.setPaint(backgroundColor);
        graphics2D.fillRect(0, 0, getSize().width, getSize().height);
        graphics2D.setPaint(foregroundColor);
        repaint();
    }

    public @NotNull Color getBackgroundColor() {
        return backgroundColor;
    }

    public @NotNull Color getForegroundColor() {
        return foregroundColor;
    }

    public void setBackgroundColor(@NotNull Color backgroundColor) {
        this.backgroundColor = backgroundColor;
    }

    public void setForegroundColor(@NotNull Color foregroundColor) {
        this.foregroundColor = foregroundColor;
        graphics2D.setPaint(foregroundColor);
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        currentMouseX = e.getX();
        currentMouseY = e.getY();

        switch (drawingMode) {
            case normal -> {
                graphics2D.drawLine(mouseX, mouseY, currentMouseX, currentMouseY);
                repaint();
                mouseX = currentMouseX;
                mouseY = currentMouseY;
            }
        }
    }

    @Override
    public void mouseMoved(MouseEvent e) {

    }


    public enum Mode {
        normal
    }
}

这是我的jComponenet的用法：

import net.danielgolan.paint.graphics.DrawingArea;

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

public class Paint {
    public final JFrame J_FRAME;
    public final Container CONTENT;
    public final BorderLayout BORDER_LAYOUT;
    public final DrawingArea DRAWING_AREA;
    public final JPanel CONTROLS;
    public final JButton CLEAR_BTN, BLACK_BTN, BLUE_BTN, GREEN_BTN, RED_BTN, MAGENTA_BTN;

    Paint(){
        this("DanielGolan's Paint", 600, 600,
                "Clear", "Black", "Blue", "Green", "Red", "Magenta");
    }

    Paint(String title, int width, int height, String clearText, String blackText, String blueText, String greenText, String redText, String magentaText){
        J_FRAME = new JFrame(title);
        CONTENT = J_FRAME.getContentPane();
        BORDER_LAYOUT = new BorderLayout();
        DRAWING_AREA = new DrawingArea(DrawingArea.Mode.normal);
        CONTROLS = new JPanel();
        CLEAR_BTN = new JButton(clearText);
        BLACK_BTN = new JButton(blackText);
        BLUE_BTN = new JButton(blueText);
        GREEN_BTN = new JButton(greenText);
        RED_BTN = new JButton(redText);
        MAGENTA_BTN = new JButton(magentaText);

        CLEAR_BTN.addActionListener(e -> DRAWING_AREA.clear());
        BLACK_BTN.addActionListener(e -> DRAWING_AREA.setForegroundColor(Color.BLACK));
        BLUE_BTN.addActionListener(e -> DRAWING_AREA.setForegroundColor(Color.BLUE));
        GREEN_BTN.addActionListener(e -> DRAWING_AREA.setForegroundColor(Color.GREEN));
        RED_BTN.addActionListener(e -> DRAWING_AREA.setForegroundColor(Color.RED));
        MAGENTA_BTN.addActionListener(e -> DRAWING_AREA.setForegroundColor(Color.MAGENTA));

        CONTENT.setLayout(BORDER_LAYOUT);

        CONTENT.add(DRAWING_AREA, BorderLayout.CENTER);

        CONTROLS.add(CLEAR_BTN);
        CONTROLS.add(BLACK_BTN);
        CONTROLS.add(BLUE_BTN);
        CONTROLS.add(GREEN_BTN);
        CONTROLS.add(RED_BTN);
        CONTROLS.add(MAGENTA_BTN);

        CONTENT.add(CONTROLS, BorderLayout.NORTH);

        J_FRAME.add(CONTENT);

        J_FRAME.setSize(width, height);

        J_FRAME.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new Paint().J_FRAME.setVisible(true);
    }
}