Java Swing - 如何更改JCombobox的高度

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.ListCellRenderer;

public class Main extends JFrame {

  JComboBox<String> cbo = new JComboBox<>(new String[] { "Hello" });

  public Main() {
    cbo.setRenderer(new CustomComboBox());
    add(cbo, BorderLayout.SOUTH);
    add(new JLabel("Hello"), BorderLayout.CENTER);

    setDefaultCloseOperation(EXIT_ON_CLOSE);
    pack();
    setVisible(true);
  }

  public static void main(String[] args) {
    new Main();
  }

}

class CustomComboBox extends JLabel implements ListCellRenderer {

  @Override
  public Component getListCellRendererComponent(JList list, Object value,
      int index, boolean isSelected, boolean cellHasFocus) {

    JLabel label = new JLabel() {
      public Dimension getPreferredSize() {
        return new Dimension(200, 100);
      }
    };
    label.setText(String.valueOf(value));

    return label;
  }
}