Java and collecting GUI objects in a vector

b3t4

Hey everyone,

I'm a little stumped and can't for the live of me think of a way of rectifying the following problem. If someone could throw me some suggestions it'd be great. I'll write some pseudcode below (very rough)...

Vector one;

for(one.size)
{
    Create new label;
    Add new label to panel;
}

Above is pretty simple. What I want to do is keep an instance of the different labels alive, so to speak, by perhaps putting them in a Vector.

My problem starts when I try to loop through the Vector, which I would now think contain my nice GUI objects but it doesn't, the garbage collector has been busy

Basically, I want to collect all my GUI objects and be able to display them at a later stage. What am I missing cause I know I'm missing something?


Thanks for any help or advise,
A.

b3t4

Fixed the problem.

I needed to use the class Collection to, funnily enough, collect the GUI objects

I don't quite understand why a collection can so this and a Vector can't. I say this as because to use the collection I did the following...

Collection guiCollection = new Vector();

If someone would like to indulge my curiosity I'd be very happy.

A.

rsynnott

How were you adding the labels to the vector? The garbage collector shouldn't do its thing until ALL references to the offending items are gone... It SHOULD make no difference whether you use a collection or vector, I think...

clearz

Are you creating the labels inside the for loop. If you are you will not be able to access them once you leave it.

b3t4

Clearz,

Yup, I am creating them in the for loop. I don't see how creating a label outside the for loop will help. I need to create a new instance of a label for every for loop iteration. If I have one label and keep overwriting it will I not still run into problems as the label will be only as good as the last iteration, if you get me.

Just thought, if I was to create an array of labels the same size as the for loop interations, outside the for loop. Then instantiate them in the for loop would that help matters.

A.

rsynnott

Do something like:
mylabel = new Label("Demo text");

That'll create a new Label in memory at each iteration.

MrPinK

It's hard to see what was going wrong by just looking at 4 lines of rough pseudcode. Can you post the actual code that wasn't working for you?

Thordon

In the psuedocode, you never add the labels to the vector, nor do you specify the size of the vector, if you do Vector one = new Vector(), I think default size is 0, and the for loop would not loop at all because of that, heres how I would do it:

Vector v = new Vector();
int numLabels = 5;

for(int i = 0; i < numLabels; i += 1)
{
	Label label = new Label("Label " + (i + 1));
	v.add(label);
	getContentPane().add(label);
}

Edit: I think I misunderstood what you wanted to do, can you show the code where you add the labels/GUI elements to the vector initially, I imagine that the problem is there.

b3t4

I was adding the labels to the vector in the same way that I was adding them to the collection. The collection worked, the vector didn't

The code is fixed now and working so I'm not too worried about it.

Thanks for all the feedback though.

A.

MrPinK

Fair enough. But the fact that you made the reference a Collection rather than a Vector wouldn't have been what fixed it.

You could have "Collection guiCollection = new Vector()" or "Vector guiCollection = new Vector()", guiCollection will still perform in exactly the same.

madramor

your theory of storing GUI elements in a vector is incorrect

vectors are synchronised,
so if you use a loop to store stuff in vector it will keep
changing all elements of the vector because they are synced

you should use an array of labels

tempest

madramor wrote:

your theory of storing GUI elements in a vector is incorrect

vectors are synchronised,
so if you use a loop to store stuff in vector it will keep
changing all elements of the vector because they are synced

you should use an array of labels

:eek:
a) Makes no sense
b) The only part that's true is that vectors are synchronized. Please read the JLS to determine the meaning of the synchronized keyword before making statements like this.

rsynnott

madramor wrote:

your theory of storing GUI elements in a vector is incorrect

vectors are synchronised,
so if you use a loop to store stuff in vector it will keep
changing all elements of the vector because they are synced

you should use an array of labels

Wuh? Nonsense.

Die wectors ARE synchronised, but that's not what synchronised means (not in this context...) Honestly, all Java books should be required to start off with a little section on what the word means from Java's point of view; it seems to confuse the hell out of people, for some reason.

madramor

// part 1
JLabel l[] = new JLab..
for(i){
   l[i] = new JLa...
   l[i].setFont(..
   l[i].setSize..
   l[i].setBack..
   l[i].setAli...
}
// part 2
getEmployeePanel(JLabel[] l){
   String ln[] = {"Name","DOB","Addres".........};
   for(i){
      l[i].setText(ln[i]);
}
getJobPanel(JLabel[] l){
   String ln[] = {"Boss","Start","Location".........};
   for(i){
      l[i].setText(ln[i]);
}
// part 3
getHolidayPanel(JLabel[] l){
   String ln[] = {"Date","Period","Remaining".........};
   for(i){
      l[i].setText(ln[i]);
      l[i].setFont.....
}

sometimes you use loops in GUI to preprocess objects
it looks like the poster is doing something like this but only storing them
in a vector not arrays so last line in loop is v.add(l); no l.

then when you use the array you have part 2

now if you had a vector to store objects instread of an array, if you
had to do a change for one usage see part 3 it would effect the vector
for all other instances

why else would you want to keep gui objects alive unless to reuse them

b3t4 wrote:

Above is pretty simple. What I want to do is keep an instance of the different labels alive, so to speak, by perhaps putting them in a Vector.

rsynnott

You certainly COULD do this (the renaming of the labels); it's questionable whether it would ever be the right thing to do tho, and once you get into adding usable components, tooltips, etc, it might be better just go with a load of switchable panels.

tempest

// part 1
Vector v = new Vector
for(i){
   JLabel label = new JLa...
   label .setFont(..
   label .setSize..
   label .setBack..
   label .setAli...
   v.add(label)
}
// part 2
getEmployeePanel(Vector vecLabels){
   String ln[] = {"Name","DOB","Addres".........};
   for(i){
      ((JLabel)(vecLabels.get(i))).setText(ln[i]);
}
getJobPanel(Vector vecLabels){
   String ln[] = {"Boss","Start","Location".........};
   for(i){
      ((JLabel)(vecLabels.get(i))).setText(ln[i]);
}
// part 3
getHolidayPanel(Vector vecLabels){
   String ln[] = {"Date","Period","Remaining".........};
   for(i){
      ((JLabel)(vecLabels.get(i))).setText(ln[i]);
      ((JLabel)(vecLabels.get(i))).setFont.....
}

How is this (functionally) different? Besides typesafety and a slight (negligible) performance hit??

Synchronization certainly has nothing to do with it!!

madramor

tempest wrote:

// part 1
Vector v = new Vector
for(i){
   JLabel label = new JLa...
   label .setFont(..
   label .setSize..
   label .setBack..
   label .setAli...
   v.add(label)
}
// part 2
getEmployeePanel(Vector vecLabels){
   String ln[] = {"Name","DOB","Addres".........};
   for(i){
      ((JLabel)(vecLabels.get(i))).setText(ln[i]);
}
getJobPanel(Vector vecLabels){
   String ln[] = {"Boss","Start","Location".........};
   for(i){
      ((JLabel)(vecLabels.get(i))).setText(ln[i]);
}
// part 3
getHolidayPanel(Vector vecLabels){
   String ln[] = {"Date","Period","Remaining".........};
   for(i){
      ((JLabel)(vecLabels.get(i))).setText(ln[i]);
      ((JLabel)(vecLabels.get(i))).setFont.....
}

How is this (functionally) different? Besides typesafety and a slight (negligible) performance hit??

Synchronization certainly has nothing to do with it!!

your template that you create in part 1
is changed in part 3
all subsequent panels that use the template will have the new
font that you used in part 3

tempest

madramor wrote:

your template that you create in part 1
is changed in part 3
all subsequent panels that use the template will have the new
font that you used in part 3

And why will that not happen with an array?

Both the Vector and the array contain references to the objects. Therefore the changes that are made via one reference are visible to all objects with the same reference. It makes no difference if they are stored in an array or in a vector. All that matters is where the reference points and in both cases the reference points to the original object that was created.

The template which is changed in part 3 is also changed in part3 when you use an array.

b3t4

rsynnott wrote:

it might be better just go with a load of switchable panels.

I will indead be hoping to add tool tips and that to the labels/any gui object created in a loop of some sort.

What do you mean by switchable panels??

A.