New to Java

I have a class that looks like:

public class Expression Builder extends JFrame {
    .....
    JTextField textField;

    public ExpressionBuilder() {
           textField = new JTextField(10);
            .....
            .....
            setSize(200,200);
            setVisible(true):
    }

    public void enableTextField() {
             textField.setEnabled(true);
    }

    public static void main(String args[]){
         ExpressionBuilder app = new ExpressionBuilder();
         app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

I then have another class that looks like:

public class BaseProtocolWindow extends JFrame {
    .......

    JButton button = new JButton("Done");
    
ExpressionBuilder expressionBuilder = new ExpressionBuilder();

    public BaseProtocolWindow() {
            .....
            .....
            setSize(200,200);
            setVisible(true):
    }
    
    .......
    .......
    public void createXPanel() {
    
            button.addActionListener(new ActionListener(){
                public void actionPerformed(ActionEvent e) {
                    expressionBuilder.enableTextField();
                   setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE);
            }
        });

}

When the button is pressed, I would like to enable a textfield in the ExpressionBuilder class and close the BaseProtocolWindow.

The problem is that because I have created two objects of the ExpressionBuilder class (one in ExpressionBuilder itself and one in BaseProtocolWindow(), two ExpressionBuilder windows are opened; first one when I run the code and the second one gets created later in the BaseProtocolWindow.

1) How can I change this code to only create one window? I think I need to somehow send a reference of the ExpressionBuilder Object created(called app in this example) to BaseProtocolWindow instead of creating a whole new object but I am not sure how.

2) setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE); only hides the window and does not closes it. If I set it to setDefaultCloseOperation(WindowConstants.CLOSE_ON_CLOSE); both the ExpressionBuilder window as well as the BaseProtocolWindow closes but I only want to close the BaseProtocolWindow. (to be honest the hiding part has even stopped working for some reason).

I would very much appreciate any help.