编译时获取“修饰符'static‘只允许在常量变量声明1错误”消息

Question

我做了一个程序来显示旋转给定的。jpg文件。编译有困难，因为它声明：

error: Illegal static declaration in inner class Lec8.MyJPanel
        public static BufferedImage toBufferedImage(Image img) {
                                    ^
modifier 'static' is only allowed in constant variable declarations
1 error"

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

    public Lec8() throws IOException {
        setSize(1000, 500);
        setTitle("Java Programing");
        getContentPane().add(scrollPane);
        myJPanel.setLayout(new GridLayout());
        myJPanel.add(myJPanell);
        setVisible(true);
    }

    public static void main(String[] args) throws IOException {
        new Lec8();
    }

    public class MyJPanel extends JPanel {
        Image ima;
        Image ima90;
        Image imaflip;
        Image imatrans;

        public MyJPanel() throws IOException {
            setBackground(Color.white);
            Toolkit toolkit = Toolkit.getDefaultToolkit();
            ima = toolkit.getImage("sample2.jpg");

            MediaTracker mt = new MediaTracker(this);
            mt.addImage(ima, 0);
            try {
                mt.waitForAll();
            } catch (InterruptedException ignored) {
            }

            imaflip = genImageFlipVirt(ima);
            ima90 = genImageRotate90(ima);
            imatrans = genImageWithAlpha(ima, 50);
        }

        public static BufferedImage toBufferedImage(Image img) {
// ERROR GENERATAED HERE STATING
// Illegal static declaration in inner class Lec8.MyJPanel public static BufferedImage toBufferedImage(Image img) { ^ modifier 'static' is only allowed in constant variable declarations 1 error
        }
    }
}

Answer 1

公共类MyJPanel extends JPanel{需要将其设置为静态以便支持静态方法或属性，除非您使用的是Java16+。

话虽如此，您可以通过使用ImageIo而不是Toolkit来避免这个问题，例如...

public class MyJPanel extends JPanel {

    BufferedImage ima;
    Image ima90;
    Image imaflip;
    Image imatrans;

    public MyJPanel() throws IOException {
        setBackground(Color.white);
        ima = ImageIO.read(new File("sample2.jpg"));

        imaflip = genImageFlipVirt(ima);
        ima90 = genImageRotate90(ima);
        imatrans = genImageWithAlpha(ima, 50);
    }

}

有关更多详细信息，请参见读取/加载图像

• Java,JPanel在旋转时裁剪图像
• 如何在Java中旋转imageIcon
• 旋转图像对象
• Java,JPanel在旋转时裁剪图像

镜像/翻转图像实际上非常简单（这是一种巧妙的副作用），例如，AffineTransform.rotate（）--如何同时进行xlate、Roting和scale？