我从here下载了类SpringUtilities的源代码。

您的问题是您没有将所有组件都添加到panel中。当您应该致电add()时，您正在致电panel.add()。因此，您只向panel添加了4个组件，而不是8个。因此，出现了错误消息。

我还添加了对类pack()的方法JFrame的调用，以使JFrame足够大以显示其包含的所有组件。

以下是我的修正代码：

import layout.SpringUtilities; // in your code this import is added twice

import javax.swing.*;

public class FactorialCalculatorFrame extends JFrame {
    public FactorialCalculatorFrame() {
        setDefaultCloseOperation(EXIT_ON_CLOSE); // I added this line
        JPanel panel = new JPanel();
        panel.setLayout(new SpringLayout());

        JTextField brojText = new JTextField();
        brojText.setColumns(10);
        panel.add(new JLabel("Broj:",SwingConstants.RIGHT));
        panel.add(brojText);

        JButton start = new JButton("Start");

        panel.add(new JLabel("Pokreni izracun:",SwingConstants.RIGHT));
        panel.add(start);

        JProgressBar napredakProgressBar = new JProgressBar();

        panel.add(new JLabel("Napredak:",SwingConstants.RIGHT)); // change here
        panel.add(napredakProgressBar); // change here

        JLabel rezultat = new JLabel("Rezultat:");
        JLabel ispisiRez = new JLabel("");

        panel.add(new JLabel("Rezultat:",SwingConstants.RIGHT));
        panel.add(ispisiRez);

        start.addActionListener((e)->{
            try {
                int number = Integer.parseInt(brojText.getText());

                //reset GUI components
                napredakProgressBar.setValue(0);
                start.setEnabled(false);
                ispisiRez.setText("");

                //schedule for execution on one of working threads
                new primeNumberJavaSwingApp().execute();

                            } catch (Exception ex) {
                ex.printStackTrace();
            }
        });
        SpringUtilities.makeCompactGrid(panel,4,2,5,5);
        add(panel);
    }

    public static void main(String[] args){
        FactorialCalculatorFrame frame = new FactorialCalculatorFrame();
        frame.pack(); // I added this line
        frame.setLocationRelativeTo(null); // I added this line
        frame.setVisible(true);
    }

    public class primeNumberJavaSwingApp extends SwingWorker<Long,Integer> {
        @Override
        protected Long doInBackground() throws Exception {
            Long l = (long) 3.2;
            return l;
        }
    }
}

这是运行上述代码时JFrame的屏幕截图。