JComboBox is a Swing component in Java that allows the user to choose one of the predefined values from the drop-down list. It is used when there are multiple options to choose from, but only one option can be selected at a time.

Here is an example of how to use JComboBox in Java:

import javax.swing.*;

public class ComboBoxExample {
   public static void main(String[] args) {
      String[] items = {"Item 1", "Item 2", "Item 3", "Item 4", "Item 5"};
      JComboBox<String> comboBox = new JComboBox<>(items);

      JFrame frame = new JFrame("ComboBox Example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setSize(300, 200);
      frame.add(comboBox);
      frame.setVisible(true);
   }
}

In this example, a new JComboBox is created with an array of items. Then, the JComboBox is added to a JFrame and the JFrame is made visible. When the user selects an item from the JComboBox, an ItemEvent is fired which can be captured to perform some action.