Iterating through all elements but the first one

jozze

Hi, I am trying to iterate through a list of particles to apply later some motion to them, the first one must remain static. I´ve thought about using both enhanced and 'classic' for loop; the first one was rejected, since it iterates through all elements of the array, while the second one throws an "indexOutOfBoundsException;index:4,Size:4" It seems to be a very naive solution but I haven´t figure it out yet; is there something I am missing or any other more suitable loop I could go through? Thanks for answers. Here is part of the code:

        Constructor(){
        //blabla
        ..
            Particle first=particles.get(0);
            first.lock(); 
        //blabla
        ..
        }

            void display() {
            //blabla
            ..
 //for (Particle p : particles) {  //rejected

                   for (int i = particles.size();i>=1; i++) {//we start from i>=1 so 1st particle remains fixed  ??   
                      Particle p= particles.get(i); 
                //blabla
             ellipse(p.x, p.y, 2, 2);
    ..

                }

koogs

// NB starts at 1
for (int i = 1 ; i < size() ; i++) {
    ....
}

first item is list[0] so just start the loop at i = 1

jozze

I feel stupid now,, #:-S thanks koogs!

colouredmirrorball

The reason this line: for (int i = particles.size();i>=1; i++) { doesn't work is that you start with i at particles.size() but if particles.size() was for example 4 then the indices would be 0, 1, 2 and 3 so if you would try to get element 4 you get an error. Using for (int i = particles.size()-1;i>=1; i--) should work, going from particles.size()-1.

GoToLoop

For backwards loop, my favorite template is: for (int i = particles.size(); i-- != 0;) {} *-:)

jozze

@colouredmirrorball: I tried that line of codefor (int i = particles.size()-1;i>=1; i++) { following the same thinking.. but got the same "indexOutOfBoundsException;index:4,Size:4" error message.

@GoToLoop: with this structure the paticle 0 is not static and responds to the whole motion applied later to the array. As it did with the enhanced for loop.

thanks both for the alternatives!

GoToLoop

Like I said that was my template. Since you don't want index 0, it gotta be stopped after index 1 in your case:
for (int i = particles.size(); i-- > 1;) {}

jozze

oh, I misunderstood you then,, yeah that works too :)

colouredmirrorball

I tried that line of code for (int i = particles.size()-1;i>=1; i++) { following the same thinking.. but got the same "indexOutOfBoundsException;index:4,Size:4" error message.

Derp, you are right. It should be this:

for (int i = particles.size()-1;i>=1; i--) {

instead of i++, because you are going backwards through the loop. (Edited in the other post as well)

rhklein

is there a short way to skip an element in the middle? something like

for (int i=0;i<=10 || i==5;i++){
  println(i);
 }

GoToLoop

for (int i = 0; i != 10; ++i) {
  if (i == 5)  continue;

  // stuff
}

rhklein

thank you.

jozze

@colouredmirrorball: for (int i = particles.size()-1;i>=1; i--) { works nicely. Sorry for late reply and thank you!