Allow JComboBox to accept List<String> or HashMap instead of String[]

Question

When inputting a new Student object inside my JTables I would like to hold all the localities/cities inside my JComboBox. Each city is stored inside a HashMap which holds the name as key(as there are no duplicates) and it's postcode.

Example: hashMap.put("City", "AAA")

Now my issue would be to represent the HashMap OR List<String> inside the JComboBox itself. The cheap and easy alternative was to simply re-write the String[] to hold all the town names and switch-case the selected value but there are few issues with that:

1. It's too long, adding new localities may be a pain or waste of time
2. Alot of unnecessary code
3. Looks horrible if being reviewed by someone
4. Potentially slower than my proposed method

Answer 1

Here you go :

 String [] string = {"city","town","country","province"};
 java.util.List<String> list = new ArrayList<String>(Arrays.asList(string));


 Object[] arrayObject= list.toArray();
 String [] data = Arrays.copyOf(arrayObject, arrayObject.length,String[].class); // java 1.6+
 JComboBox<String> combo = new JComboBox<>( data);

Actually you can do :

 String [] string = {"city","town","country","province"};
 java.util.List<String> list = new ArrayList<String>(Arrays.asList(string));


 JComboBox< java.util.List<String>> combo = new JComboBox<>( );
 combo.addItem(list);

but , for every single elemen of JComboxBox will hold all elements of list in a row.

*To prevent ambiguity between java.util.List & java.awt.List , we should declare them clearly.

Here the complete demo :

import java.awt.*;
import javax.swing.*;
import java.util.*;

public class ComboBoxDemo extends JFrame {
public ComboBoxDemo() {

  super("JComboBox Demo");

    String [] string = {"city","town","country","province"};
  java.util.List<String> list = new ArrayList<String>(Arrays.asList(string));


 Object[] arrayObject= list.toArray();
 String [] data = Arrays.copyOf(arrayObject, arrayObject.length,String[].class); // java 1.6+
 JComboBox<String> combo = new JComboBox<>( data);

    setLayout(new FlowLayout(FlowLayout.CENTER));
    add(combo, BorderLayout.CENTER);      
}

 public static void main(String[] args) {
      ComboBoxDemo g = new ComboBoxDemo();
    g.setVisible(true);
    g.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    g.setBounds(100, 100, 300, 300);
 }
 }

And the result of

JComboBox< java.util.List<String>> combo = new JComboBox<>( ); combo.addItem(list);

declaration :