As I've been told, one should not declare parameters to client GWT
code as interfaces like List<T>. The typical way to write a JavaBean
containing a list is this:
public class Frames {
private List<Integer> frames = new ArrayList<Integer>();
public void setFrames(List<Integer> frames) {
this.frames = frames;
}
// ...
}
Google recommends that GWT classes use the specific ArrayList<T>
instead, because these declarations will force GWT to generate code
for LinkedList<T> and every other implementation of List.
However, this runs into another problem: encapsulation. The class
Frames2 is unsafe:
public class Frames2 {
private ArrayList<Integer> frames = new ArrayList<Integer>();
public void setFrames(ArrayList<Integer> frames) {
this.frames = frames;
}
public ArrayList<Integer> getFrames() {
return frames;
}
}
It suffers from aliasing, as setting the frames instance variable
allows the setter to interfere with the internals of the Frames2
instance:
Frames2 frames = new Frames2();
ArrayList<Integer> myScoreLine = new ArrayList<Integer>();
myScoreLien.add(9);
frames.setFrames(myScoreLine);
myScoreLine.set(0, 30); // CHEAT!
Usually, one copies the lists on both setting and getting:
public class Frames3 {
private ArrayList<Integer> frames = new ArrayList<Integer>();
public void setFrames(ArrayList<Integer> frames) {
this.frames = new ArrayList<Integer>(frames);
}
public ArrayList<Integer> getFrames() {
return new ArrayList<Integer>(frames);
}
}
This solves the aliasing problem, but is slow. Perhaps I should not
vend the list but provide access to its members. I probably should
provide a way of getting all the list's members at once:
public class Frames4 {
private ArrayList<Integer> frames = new ArrayList<Integer>();
public void addFrame(int score) {
frames.add(score);
}
public Iterator<Intgeer> frames() {
return frames.iterator();
}
}
Will this force GWT to generate code for every Iterator<E> in my
system? I probably am programming with too much paranoia, of course.
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