如何将自定义组件添加到JFrame？

Question

I'm experiencing issues with adding a new object (of my custom class TemplatesList ) to a JFrame . I added a Picture object to the JFrame before and that works perfect. But when I want to add an object of my own class, it returns an error for some reason. Can you please help me with identifying the problem? I would appriciate.

The error says: cannot resolved method add(lista) when I try to add this:

 TemplatesList lista = new TemplatesList();
 frame.add(lista);

here's the code:

    import javax.swing.*;
    import java.awt.Color;
    import java.awt.FlowLayout;
    import javax.swing.JList;

    public class ChoosingPage
    {
    static JFrame frame;
    JLabel choose;

    public ChoosingPage ()
    {
        frame = new JFrame ("Primark's templates");
        frame.setSize(500,500);
        frame.setLocation(50,50);
        frame.setLayout(new FlowLayout(FlowLayout.CENTER));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //frame.setBackground(Color.WHITE);
        frame.getContentPane().setBackground(Color.WHITE);

        choose = new JLabel("choose your template");
        choose.setSize(choose.getPreferredSize());
        //choose.setLocation(20,20);
        frame.add(choose);

        Picture zdjecie = new Picture();
        frame.add(zdjecie);

        TemplatesList lista = new TemplatesList();
        frame.add(lista);




        frame.setVisible(true);
    }

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

and the class which I want to add to the JFrame:

import javax.swing.*;

public class TemplatesList
{
    private JComboBox faceCombo;

    public TemplatesList()
    {
        faceCombo = new JComboBox();
        faceCombo.setEditable(false);
        faceCombo.addItem("change request");
        faceCombo.addItem("Emergancy Change request");
        faceCombo.addItem("problem request");
        faceCombo.addItem("problem handover");

    }
}

Answer 1

You can only add objects of type Component to JFrame. Your class extends Object (by default). So you have to change your class to look like

import javax.swing.*;

public class TemplatesList extends JComboBox<String>
{

    public TemplatesList()
    {
        setEditable(false);
        addItem("change request");
        addItem("Emergancy Change request");
        addItem("problem request");
        addItem("problem handover");

    }
}

as JComboBox extends Component . And so by extending JComboBox your TemplatesList class also extends Component .

Then you can use:

TemplatesList lista = new TemplatesList();
frame.add(lista);