Allow JComboBox to accept List 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:

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

The key is not the JComboBox but rather its model. You could create your own model class by extending [AbstractListModel](http://docs.oracle.com/javase/8/docs/api/javax/swing/AbstractListModel.html) and implement the right interfaces, and then have it accept your choice of collections. Note though that order is important, and so a HashMap would likely not be acceptable. An ordered map would, I believe. — Hovercraft Full Of Eels, Aug 23 '14 at 20:28
I don't see a question. Or any code. What have you tried so far? Please read [How do I ask a good question?](http://stackoverflow.com/help/how-to-ask). — DavidPostill, Aug 23 '14 at 20:28
@HovercraftFullOfEels - I understand, it's the same concept I had to undergo with my JTables. Since it would originally accept `Object[][]` I had to create my own model to accept List to retrieve the required fields. The only part I didn't quite get is the order and ordered map. 1) Why would it be an issue. 2) Why would an ordered map be required instead of let's say `List`? — Juxhin, Aug 23 '14 at 20:32
I didn't say that. A `List` would work just fine and easily too. I'm just saying that if you absolutely had to use a Map as your model, it would have to be ordered. The model is *indexed* which forces order on it. — Hovercraft Full Of Eels, Aug 23 '14 at 20:32
As HovercraftFullOfEels has already stated, of the default models don't suit your needs, you are free To create your own... — MadProgrammer, Aug 23 '14 at 20:48

Fevly Pallar · Accepted Answer · 2014-11-05T05:55:35.293

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);
 }
 }

enter image description here

And the result of

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

declaration :

enter image description here

After trying both methods, both seem to be throwing `java.lang.NoSuchMethodException` — Juxhin, Aug 23 '14 at 21:14

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

1 Answers1