根据用户输入生成Java swing字段

Question

Java beginner here.

I am trying to generate Labels based on user input(take input for the number of labels to generate between 0 to 50) in a JPanel inside a JScrollPane.

The labels are generating correctly but the problem is the panel cant be scrolled down to view all the Labels.

Is it because I am using absolute layout for the panel? If yes then what might be the solution? Please guide.

Note: I made the labels using an array of 50 JLabels in a for loop. Terrible programming practice maybe but works.

Here's the code snippet

        frame = new JFrame();
        frame.setSize(800, 800);
        frame.getContentPane().setLayout(null);

        JScrollPane scrollPane = new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        scrollPane.setBounds(103, 37, 439, 350);
        frame.getContentPane().add(scrollPane);

        JPanel panel = new JPanel();
        scrollPane.setViewportView(panel);
        panel.setLayout(null);

        JButton btnGenerateLabels = new JButton("Generate Labels");
        btnGenerateLabels.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JLabel[] lab =  new JLabel[50];
                int  y = 50;
                for(int i=0; i<50; i++)
                {
                    lab[i] = new JLabel();
                    lab[i].setText("Label "+(i+1));
                    panel.add(lab[i]);
                    lab[i].setBounds(180, y, 97, 25);
                    y += 30;
                }
            }
        });
        btnGenerateLabels.setBounds(129, 23, 152, 25);
        panel.add(btnGenerateLabels);

Answer 1

Is it because I am using absolute layout for the panel?

Yes. Don't use a null layout. Swing was designed to be used with layout managers.

The solution is to use a layout manager, probably the GridLayout as was suggested.

After all the components have been added to the panel you then need to invoke revalidate() and repaint() on the panel. This will invoke the layout manager and each component will be given a size/location.

Scrollbars will then appear as required.