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why I must use final modifier

Jimsecond Huang

Joined: Dec 03, 2004
Posts: 8

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() {
The ide ask me to add final modifier for variable hws. I don't know why this is mandatory.

anyone knows

Ernest Friedman-Hill
author and iconoclast

Joined: Jul 08, 2003
Posts: 24183

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.

[Jess in Action][AskingGoodQuestions]
Jimsecond Huang

Joined: Dec 03, 2004
Posts: 8

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

It is sorta covered in the JavaRanch Style Guide.
subject: why I must use final modifier
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