I'm trying to create an array of JLabels, all of them should go invisible when clicked. The problem comes when trying to set up the mouse listener through an inner class that needs access to the iteration variable of the loop used to declare the labels. Code is self-explanatory:
for(int i=1; i<label.length; i++) {
label[i] = new JLabel("label " + i);
label[i].addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent me) {
label[i].setVisible(false); // compilation error here
}
});
cpane.add(label[i]);
}
I thought that I could overcome this by the use of this
or maybe super
instead of the call of label[i]
within the inner method but I haven't been able to figure it out.
The compilation error is: local variable i is accessed from within inner class; needs to be declared final`
I'm sure that the answer must be something really silly I haven't thought of or maybe I'm making some small mistake.
Any help would be appreciated
Accessing the Private Members Write an inner class in it, return the private members from a method within the inner class, say, getValue(), and finally from another class (from which you want to access the private members) call the getValue() method of the inner class.
If you want your inner class to access outer class instance variables then in the constructor for the inner class, include an argument that is a reference to the outer class instance. The outer class invokes the inner class constructor passing this as that argument.
You can declare the variable final, or make it an instance (or global) variable. If you declare it final, you won't be able to change it later. Any variable defined in a method and accessed by an anonymous inner class must be final.
It can access any private instance variable of the outer class. Like any other instance variable, we can have access modifier private, protected, public, and default modifier.
Your local variable must be final
to be accessed from the inner (and anonymous) class.
You can change your code for something like this :
for (int i = 1; i < label.length; i++) {
final JLabel currentLabel =new JLabel("label " + i);
currentLabel.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent me) {
currentLabel.setVisible(false); // No more compilation error here
}
});
label[i] = currentLabel;
}
From the JLS :
Any local variable, formal parameter, or exception parameter used but not declared in an inner class must be declared
final
.Any local variable used but not declared in an inner class must be definitely assigned (§16) before the body of the inner class.
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