import java.awt.BorderLayout;
import java.awt.Component;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListCellRenderer;
public class Main {
public static final void main(String[] args) {
JFrame frame = new JFrame();
JPanel mainPanel = new JPanel();
JPanel buttonsPanel = new JPanel();
frame.add(mainPanel);
frame.add(buttonsPanel, BorderLayout.SOUTH);
String[] options = { "S", "G", "I","T" };
JComboBox comboBox = new JComboBox(options);
comboBox.setRenderer(new MyComboBoxRenderer("COUNTRY"));
comboBox.setSelectedIndex(-1);
mainPanel.add(comboBox);
JButton clearSelectionButton = new JButton("Clear selection");
clearSelectionButton.addActionListener(e-> {
comboBox.setSelectedIndex(-1);
});
buttonsPanel.add(clearSelectionButton);
frame.pack();
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
class MyComboBoxRenderer extends JLabel implements ListCellRenderer {
private String _title;
public MyComboBoxRenderer(String title) {
_title = title;
}
@Override
public Component getListCellRendererComponent(JList list, Object value,
int index, boolean isSelected, boolean hasFocus) {
if (index == -1 && value == null)
setText(_title);
else
setText(value.toString());
return this;
}
}
【jcombobox】
