Re: Scope of a JLabel? Also "unchecked operation"
"markspace" <-@.> wrote on 3rd Jan:
On 1/3/2012 11:02 AM, A B wrote:
2) The itemStateChanged method can't recognise a perfectly good
JTextArea that I want it to output to, just keeps saying that there is
no variable called "display".
Right, now that I can read the darn thing, I can see that "display" is a
local variable, and not accessible outside of the constructor (or before
it's declared, in fact).
public Vectorine() {
...
JTextArea display = new JTextArea("Type here.", 4, 18);
...
}
public void itemStateChanged(ItemEvent event) {
...
display.setText("Option chosen: " + choice);
...
}
So the first instance of "display" can't bust out of those braces there
("{}") because it has local scope. You need to declare display with a
broader scope to allow it to be recognized in both methods (probably
instance scope). For example:
class Vectorine extends JFrame implements ItemListener {
private JTextArea display;
public Vectorine() {
...
display = new JTextArea("Type here.", 4, 18);
...
}
public void itemStateChanged(ItemEvent event) {
...
display.setText("Option chosen: " + choice);
...
}
}
<http://docs.oracle.com/javase/tutorial/java/javaOO/variables.html>
Thanks Mark. I thought that as the ComboBox created by Vectorine() was the
one calling itemStateChanged(), that would bring itemStateChanged() within
reach of Vectorine()'s variables, but apparently not. I'm cross with "Java
In Easy Steps" now, I copied that coding straight out of one of its
examples, but apparently they never checked that it actually worked! I
didn't think of creating the labels and things at class level, I'll give
that a go.
--
A. B.
<>
My e-mail address is zen177395 at zendotcodotuk, though I don't check that
account very often.
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