我如何在JSCrollpane上使用Jcombobox的Jframe

Question

基本上，我尝试在此处向我的代码添加一个下拉列表。尽管每当我尝试又一个接一个地添加一个时，它最终会超越它。如果我在滚动前运行下拉菜单，则将滚动放在顶部，反之亦然。我有点是Jframes，在Java中绘画，所以请忍受我。

MyFrame类：

import java.awt.BorderLayout;
import java.awt.FontFormatException;
import java.io.IOException;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JViewport;

@SuppressWarnings("serial")
public class MyFrame extends JFrame {

    public void cadetImage() throws FontFormatException, IOException {

        JPanel panel = new Puller();
        JScrollPane scroll = new JScrollPane(panel, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        String[] opts = { "All", "A", "B", "C", "D", "E", "F" };
        JComboBox<String> dropdown = new JComboBox<>(opts);

        setTitle("Puller");
        scroll.getViewport().setScrollMode(JViewport.SIMPLE_SCROLL_MODE);
        add(dropdown, BorderLayout.CENTER);
        add(scroll, BorderLayout.CENTER);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setSize(500, 500);
        setLocationRelativeTo(null);
        setVisible(true);
        setExtendedState(MAXIMIZED_BOTH);
    }
}

Puller类：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontFormatException;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.swing.ImageIcon;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class Puller extends JPanel {

    private int pw, ph;
    private Font rso;

    public Puller() throws FontFormatException, IOException {
        InputStream is = new FileInputStream("assets/fonts/racing sans one.ttf");
        Dimension screen = new Dimension(Toolkit.getDefaultToolkit().getScreenSize());
        pw = (int) screen.getWidth();
        ph = (int) screen.getHeight();
        setPreferredSize(new Dimension(pw - 20, ph - 30));

        rso = Font.createFont(Font.TRUETYPE_FONT, is);
    }

    @Override
    public void paint(Graphics p) {
        Graphics2D page = (Graphics2D) p;

        template(page);
    }

    private void template(Graphics2D page) {
        page.setColor(Color.decode("#666666"));
        page.fillRect(0, 0, pw, ph);

        // Name Header
        page.setColor(Color.BLACK);
        page.fillRect(997, 122, 311, 90);
        page.setColor(Color.decode("#bf9000"));
        page.fillRect(1000, 125, 305, 84);
        page.setColor(Color.BLACK);
        page.setFont(rso.deriveFont(Font.BOLD, 75f));
        page.drawString("NAME", 1052, 193);

        // Filter Field
        page.setColor(Color.BLACK);
        page.fillRect(997, 212, 70, 50);
        page.setColor(Color.decode("#666666"));
        page.fillRect(1000, 212, 64, 47);
    }
}

无论我获得什么帮助，都将不胜感激。