Why I can't access a method from my custom JPanel?

Question

I have a JFrame with a JPanel inside.

MyFrame class:

public class MyFrame extends JFrame {

    private JPanel contentPane;

    public static void main(String[] args) {
        new MyFrame().setVisible(true);
    }

    public MyFrame() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new MyPanel();

        setContentPane(contentPane);
    }

}

MyPanel class:

public class MyPanel extends JPanel {

    private String myVariable = "abc";

    public MyPanel() {

    }

    public String getMyVariable() {
        return myVariable;
    }

    public void setMyVariable(String myVariable) {
        this.myVariable = myVariable;
    }

}

I created a class called MyPanel that extends JPanel and added a private field called MyVariable. The getters and setters functions were added to manipulate that field. When I do contentPane = new MyPanel() I can't do contentPane.getMyVariable().

What I'm missing here? Where it differs from creating for exemple a Car object and access their puclic methods? The image below shows what I'm trying to do.

Ilustration of what I'm trying to do

Answer 1

The variable contentPane in your class MyFrame has the type JPanel. But this class does not include the method getMyVariable() you try to call.

You have multiple options to resolve the issue, for example:

• Define the variable as MyPanel contentPane.
• Cast the variable, ((MyPanel)contentPane).getMyVariable();