Question

I’m writing a simple web browser in Java. I have a class, WebBrowserPane, which extends JEditorPane and sets it up for better displaying web pages (disables editing, adds a HyperlinkListener etc.). I then have a class, WebBrowserFrame, which extends JFrame and places some buttons and an address bar at the top and a WebBrowserPane below. Rather than it only being able to place a WebBrowserPane below, though, I would like it to take anything which extends JEditorPane and has the relevant methods.

I wrote an abstract class, AbstractBrowser to achieve this:

import javax.swing.JEditorPane;

public abstract class AbstractBrowser extends JEditorPane {
public void back(){}
public void forward(){}
public void refresh(){}
}

WebBrowserPane then extends AbstractBrowser:

public class WebBrowserPane extends AbstractBrowser {
WebBrowserPane(){
    setEditable(false);

    //etc
}
public void back(){
    //blah
}
}

WebBrowserFrame then takes any AbstractBrowser as a parameter:

public class WebBrowserFrame extends JFrame{
WebBrowserFrame(AbstractBrowser a){
    add(a);
}
}

Obviously this doesn’t ensure that the abstract classes methods are ever overridden so I realise its not a very good solution. Is there a way to accomplish this using an interface instead?

Answer 1

The problem is that an interface can’t extend JEditorPane. But you can declare abstract methods in an abstrac class, and the compiler would force any child class to override them:

import javax.swing.JEditorPane;

public abstract class AbstractBrowser extends JEditorPane {
    public abstract void back();
    public abstract void forward();
    public abstract void refresh();
}