An unseen java syntax: " className .this"

Question

As I studied the Java Tutorial, "How to use File Choosers", I found a strange Java expression in FileChooserDemo.java as listed below
public class FileChooserDemo extends JFrame {
    public FileChooserDemo() {
        final JFileChooser fc = new JFileChooser();
            // In response to a button click:
            // int returnVal = fc.showOpenDialog(aComponent);
            int returnVal = fc.showOpenDialog(FileChooserDemo.this);
}What's "FileChooserDemo.this" really mean?
Remark: "FileChooserDemo.this" could not be substitued with "this", it caused a compilation error.

Answer 1

Hi s_plyw,
the syntax you have seen meens that showOpenDialog() get a referenz of the current instance of FileChooserDemo. You need this syntax for inner classes, to get a referenz of the class where the inner class is nested. If you only use 'this' you will get an instance of the inner class.
public class A {
public int val = 5;
public A() {
new B();
private class B {
public int val = 10;
public B() {
System.out.println("->" + A.this.val);
System.out.println("->" + this.val);
public static void main(String[] args) {
new A();
produce:
->5
->10
Look at the langspec (can be downloaded from the sun sites) for the syntax. I think in 'thinking in java' are more examples.
J�rgen