Java Swing错误线程“AWT-EventQueue-0”中的异常java.lang.IllegalArgumentException：input == null

Question

我是Java开发的初学者。想要将图片添加为JPanel的背景。我在过去4个小时内尝试了很多解决方案，最终出现了这个错误：

  

线程“AWT-EventQueue-0”中的异常   java.lang.IllegalArgumentException：input == null！在   javax.imageio.ImageIO.read（ImageIO.java:1348）at   schedule.loginPrintTable $ 1.run（loginPrintTable.java:107）at   java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:311）

请注意我在这个文件中没有main（），我不想使用main（）来添加图像作为背景。

class loginPrintTable extends JLabel{


    JFrame tableframe;

    private table[][][] ttable;
    DefaultTableModel model = new DefaultTableModel();
    JTable Table;

    int stgrp;
    int i;

    JPanel south;
    inputdata input;

    public loginPrintTable(int nostgrp, inputdata input1) {
        // ttable = t;
        tableframe = new JFrame();
        stgrp = nostgrp;
        south = new JPanel();
    }



    void print() {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                tableframe.setTitle("CLASS SCHEDULING");
                tableframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                tableframe.setSize(800, 600);

                tableframe.setLayout(new GridBagLayout());

                GridBagConstraints c = new GridBagConstraints();
                c.weightx = 0;
                c.gridx = 1000;
                c.gridy = 50;
                c.fill = GridBagConstraints.CENTER;
                int j;

                JPanel panel;
                JLabel label1, label2;
                final JTextField text1, text2;
                label1 = new JLabel();

                label1.setText("Username:");
                text1 = new JTextField(15);
                JButton next = new JButton("Login");
                JButton next1 = new JButton("Cancel");

                label2 = new JLabel();
                label2.setText("Password:");
                text2 = new JPasswordField(15);
                panel = new JPanel(new GridLayout(3, 1));

                panel.add(label1);
                panel.add(text1);
                panel.add(label2);
                panel.add(text2);
                panel.add(next);
                panel.add(next1);



                        try {
                            InputStream imageStream = this.getClass().getResourceAsStream("asset/login.jpeg");
                            BufferedImage image;

                            image = ImageIO.read(imageStream);

                            JLabel picLabel = new JLabel(new ImageIcon(image));

                            panel.add(picLabel);

                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }

                JPanel panel2;
                JLabel label3;

                label3 = new JLabel();

                label3.setText("Progressing...Please wait....");

                panel2 = new JPanel(new GridLayout(3, 1));
                panel2.add(label3);

                JScrollPane scroll = new JScrollPane(Table);
                // panel=new loginPanel(ttable,stgrp,input);
                 JPanel south = new JPanel();
                 south.setLayout(new GridLayout(1, 10));
                 for (j = 0; j < 2; j++) {
                 south.add(new JLabel(" "));
                 }
                 south.add(next);

                 south.add(next1);

                tableframe.add(panel);

                 c.gridx = 0;
                 c.gridy = 10;
                 tableframe.add(south, c);
                tableframe.setVisible(true);


            }
        });
    }
}