why I must use final modifier

[Jimsecond Huang]

Hi,

Just test some code below,


public static void main(String[] args){
final HelloWorldSwing hws = new HelloWorldSwing();
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
hws.createAndShowGUI();
}
});
}
The ide ask me to add final modifier for variable hws. I don't know why this is mandatory.

anyone knows

Thanks

[Ernest Friedman-Hill]

Because hwe is a local variable, the stack frame it's defined in may not even exist by the time the run() method is actually invoked. My making the variable final, you're actually giving Java permission to take a copy of the variable's value at the time the inner class object is created, and use that copy, rather than having to go find a (possibly non-existent) value when the run() method runs.

[Jimsecond Huang]

Ernest,

Thanks so much. I just think I got it but your answer is so perfect.

Jim