Could someone take a look at this code?

Question

The following code is mean to implement a listener for a text area object and to listen for text being entered:
abstract class DocChange implements javax.swing.event.DocumentListener
         public void textValueChanged(javax.swing.event.DocumentEvent event)
               Object object = messageTextArea.getDocument();
               if (object.toString().length() !=0)
                    txtMessageTextArea_TextValueChanged(event);
void txtMessageTextArea_TextValueChanged(javax.swing.event.DocumentEvent event)
          toolBar.getComponent(5).setVisible(true);
     }What it's supposed to do is detect when text is typed within it and set the button in question to be visible if text is typed and then invisible
if the text is removed. (The button has been set to be invisible previously). I am not sure how to implement the document listener for the messageTextArea object. Could anyone tell me how to do that and if they see anything wrong with this approach?
Thanks a lot.

Answer 1

when you implement an interface, you must define all of the methods in that interface. That is because all of the methods of the interface are implicitly public and abstract. The reason it told you to declare DocChange as abstract is because if you don't define the methods that you implemented from DocumentListener, which are abstract, then the class that implements the interface must be declared abstract.