为swing类重写toString（）

Question

I want to override toString() method for a FileFilter object. I have this piece of code

JFileChooser saveFile = new JFileChooser();
saveFile.setAcceptAllFileFilterUsed(false);
saveFile.setMultiSelectionEnabled(false);
saveFile.setFileFilter(new FileNameExtensionFilter("PNG", ".png"));
String type = saveFile.getFileFilter().toString();
System.out.println(type);

Which prints out something along the lines of javax.swing.filechooser.FileNameExtensionFilter@39cc65b1[description=PNG extensions=[.png]] . My goal is to create an overridden toString method, so I would get only the .png part.
I KNOW that there are more efficient ways to do this exact task, and I know the basic string functions to get the part I need, but my goal is to do it with an overridden method.

Answer 1

my goal is to do it with an overridden method.

This is not possible, for a number of reasons described below. The only way to do it is through composition, not through inheritance.

You can override a method only in classes that you own. Since you do not own the FileNameExtensionFilter , an implementation of FileFilter returned by JFileChooser , there is no way for you to override its toString method.

Moreover, FileNameExtensionFilter is a final class , so you cannot override any of its methods.

The only approach available in this situation is to create your own FileFilter wrapping FileNameExtensionFilter , and pass it the filter that you get from JFileChooser . You would own this class, so you could override its toString as needed:

class FileFilterWrapper {

    private final FileFilter innerFilter;

    public FileFilterWrapper(FileFilter innerFilter) {
        this.innerFilter = innerFilter;
    }

    @Override
    public String toString(){
        // Use innerFilter properties to produce the desired String
        return ...
    }
}

Answer 2

If you literally just want to do it right here you could do an anonymous inner class for it:

JFileChooser saveFile = new JFileChooser() {
   @Override
   public String toString() {
      return ".png";
   }
}

I can't recommend that approach though, it would be better to implement your own subclass of JFileChooser and define a new String getFileExtension() method inside that.

Answer 3

To do that, you need to use a subclass of JFileChooser. If that's the only method you want to override, its quite simple.

public class MyFileChooser extends JFileChooser{
    public MyFileChooser(){
        super();
    }

    @Override
    public String toString(){
        //your string conversion code here
    }
}