Why I can NOT have a class inside a method?

[Shawn]

Hi,

I have a method. Inside it, I need a ActionListener. The code is like:

public class DataMgr
{
private JFileChooser chooser = new JFileChooser();

public void saveData()
{
chooser.addActionListener(new SaveFileListener(chooser));
if ( chooser.showSaveDialog(new JPanel()) ==
JFileChooser.APPROVE_OPTION) //user clicked Save button
...//some code


final class SaveFileListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
...//some code
}
} //end of class SaveFileListener

} //end of method saveData
} //end of class DataMgr

Let me explain my code. I need to save something using JFileChooser to
pops up a gui which lets the user to select the path and input file
name. Unfortunately, if the user selects an existing file, the program
just QUIETLY overwrite it without any warning. So I googled and found
that I have to implement my own listener (e.g. SaveFileListener) to
achieve such a feature. I am surprised Sun doesn't provide such a
feature since it is so obviously needed.

Because the class SaveFileListener is only needed inside the method
saveData(), none of other methods need or care its existence, I hope to
put the class inside the method scope to make the method self-contained.
Then I run into the problem:
first, compiler says that modifier can only be abstract or final. I
changed private to final.
Then, compiler says the following line cannot find the type
SaveFileListener.
chooser.addActionListener(new SaveFileListener(chooser));

My plan is correct or not? How can I achieve my plan? Thank you very much.

I assume if I put the class SaveFileListener outside the method scope
saveData(), things will be fine. But I think that way unrelated code
will clutter the programmer's brain.

Thank you very much.

 

[Steve Wampler]

Hi,

I have a method. Inside it, I need a ActionListener. The code is like: ....
Let me explain my code. I need to save something using JFileChooser to
pops up a gui which lets the user to select the path and input file
name. Unfortunately, if the user selects an existing file, the program
just QUIETLY overwrite it without any warning. So I googled and found
that I have to implement my own listener (e.g. SaveFileListener) to
achieve such a feature. I am surprised Sun doesn't provide such a
feature since it is so obviously needed.

Read about anonymous inner classes.

 

[Knute Johnson]

Hi,

I have a method. Inside it, I need a ActionListener. The code is like:

public class DataMgr
{

Should be class SaveFileListener extends ActionListener or
ActionListener saveFileListener = new ActionListener() {
in any case it must be defined before you use it in your code

 

[Oliver Wong]

public void saveData()
{
chooser.addActionListener(new SaveFileListener(chooser));
if ( chooser.showSaveDialog(new JPanel()) == JFileChooser.APPROVE_OPTION)
//user clicked Save button
...//some code


final class SaveFileListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
...//some code
}
} //end of class SaveFileListener

} //end of method saveData [...]
Then, compiler says the following line cannot find the type
SaveFileListener.
chooser.addActionListener(new SaveFileListener(chooser));

Did you try putting the class declaration before its usage?

- Oliver

 

[Shawn]

Hi,

I have a method. Inside it, I need a ActionListener. The code is like:

public class DataMgr
{
private JFileChooser chooser = new JFileChooser();

public void saveData()
{
chooser.addActionListener(new SaveFileListener(chooser));
if ( chooser.showSaveDialog(new JPanel()) ==
JFileChooser.APPROVE_OPTION) //user clicked Save button
...//some code


final class SaveFileListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
...//some code
}
} //end of class SaveFileListener

} //end of method saveData
} //end of class DataMgr

Let me explain my code. I need to save something using JFileChooser to
pops up a gui which lets the user to select the path and input file
name. Unfortunately, if the user selects an existing file, the program
just QUIETLY overwrite it without any warning. So I googled and found
that I have to implement my own listener (e.g. SaveFileListener) to
achieve such a feature. I am surprised Sun doesn't provide such a
feature since it is so obviously needed.

Because the class SaveFileListener is only needed inside the method
saveData(), none of other methods need or care its existence, I hope to
put the class inside the method scope to make the method self-contained.
Then I run into the problem:
first, compiler says that modifier can only be abstract or final. I
changed private to final.
Then, compiler says the following line cannot find the type
SaveFileListener.
chooser.addActionListener(new SaveFileListener(chooser));

My plan is correct or not? How can I achieve my plan? Thank you very much.

I assume if I put the class SaveFileListener outside the method scope
saveData(), things will be fine. But I think that way unrelated code
will clutter the programmer's brain.

Thank you very much.

Thank you all. Yes, I put the class definition in the end (right before
the end of the method scope } ). Now, if I put the inner class in the
beginning part of the method, then when I use it, no error at all.

Thank you all for your help.