Question

I’m working in huge program in java and now I’m trying to avoid loitering to improve it’s memory usage, I instantiate some objects in the constructor, and keep instantiated till the end of the program but they are not always used. My question is specificly about garbage collecting arrays of Objects.

For example when the user presses a menu item a JDialog is invoked with lots of components in it, these components were instantiated at the moment that the program runs, but i want to instantiate them when necessary and free them when not.

For example:

JRadioButton Options = new JRadioButton[20];
for (int i = 0; i < 20; i++) {
    Options[i] = new JRadioButton(Labels[i]);
}

If i want to free the arrays, what shoud i do?

This:

for (int i = 0; i < 20; i++) {
    Options[i] = null;
    Labels[i] = null;
}

Or simply:

Options = null;
Labels = null;

Thanks in advance

Answer 1

First, a Java object will be garbage collected only if it is not reachable (and it might have other references than your array). Then GC runs at nearly unpredictable times (so the memory might be freed much later).

Clearing the array’s elements won’t release the whole array, but could release each element (provided it becomes unreachable).

setting a variable to null might release the array (and of course all the elements).

But for a so small program, perhaps GC is never happening.

Read at least GC on wikipedia, and perhaps the GC handbook

Notice that the aliveness of some object is a whole program property (actually a whole process property: liveness of values is relevant in a particular execution, not in your source code). In other words, you could do Options = null; and still have the object in Options[24] reachable by some other reference path.