# Problem with a loop
**URL:** https://discourse.processing.org/t/problem-with-a-loop/3415
**Category:** Coding Questions
**Created:** [September 10, 2018, 11:02am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415 "2018-09-10T11:02:15Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 10, 2018, 11:02am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/1 "2018-09-10T11:02:15Z")
Hi i tried to use the code i recieve from my post “a pathfinding solution” to make my creatur find food.
here is the case :
my creatures walk randomly and when they are hungry they go to the closest food, but my foods have a life time so its disapeard after a while. Other foods appear constantly and my creatures eat it when they pass on it.
```auto
float currentSmallest;
float dist;
for(int a = herb3f.size()-1; a >= 0; a--){
Herbivor3F h3f = herb3f.get(a);
if(h3f.faim() == false){
h3f.randomMv();
}
else{
PVector target = new PVector(0,0);
currentSmallest = (parent.height * parent.height) + (parent.width * parent.width);
while(F2.hasNext()){
Food2 f = F2.next();
dist = ((h3f.position.x - f.position.x) * (h3f.position.x - f.position.x)) + ((h3f.position.y - f.position.y) * (h3f.position.y - f.position.y));
if( dist < currentSmallest){
currentSmallest = dist;
target.x = f.position.x;
target.y = f.position.y;
}
}
h3f.findFood(target);
}
}
```
my problem:
Well my creatures dont go to the foods and go on the top left corner on my screen (the currentSmallest) when they are hungry (the condition “faim” is true)
i tried to make loop but every time is bug.
Thanks for yours times and help.
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 10, 2018, 1:51pm UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/2 "2018-09-10T13:51:39Z")
i dont know if i give enough informations, so if you need more just tell me
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 10, 2018, 3:58pm UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/3 "2018-09-10T15:58:12Z")
It seems that you never enter that block:
```auto
if( dist < currentSmallest){
currentSmallest = dist;
target.x = f.position.x;
target.y = f.position.y;
}
```
So target stays (0, 0) and thus your creatures go to the upper left corner.
My guess is that you don’t even enter the while loop. Can you add this line just before you while loop to check that hypothesis:
```auto
println(F2.hasNext());
```
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 8:04am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/4 "2018-09-11T08:04:24Z")
Yes i never enter the loop, its say false every time.
But i need my while to point the food or i get an error
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 8:19am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/5 "2018-09-11T08:19:44Z")
We would need to see your Food2 class then.
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 8:21am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/6 "2018-09-11T08:21:06Z")
i tried a do while but i got the exception :
java.util.NoSuchElementException
at java.util.ArrayList$Itr.next(Unknown Source)
at mechanisme.World.run(World.java:338)
the error occur with Food2 f = F2.next();
and here is my food2:
```auto
public class Food2 {
PApplet parent;
ArrayList food2;
ArrayList tree2;
float food2live;
public PVector position;
public Food2(int nombFood2, PApplet p){
parent = p;
food2 = new ArrayList();
food2live = 255;
}
@SuppressWarnings("deprecation")
public void add(PVector l){
food2.add(l.get());
}
public void grow(Tree2 t){
ArrayList tree2 = t.getTree2();
for(int i = 0; i < tree2.size(); i++){
if(parent.random(1) < 0.001){
int nombfood2 = 1;
for(int a = 0; a < nombfood2; a++){
food2.add(new PVector(parent.random(tree2.get(i).x -50, tree2.get(i).x +50), parent.random(tree2.get(i).y-50, tree2.get(i).y +50)));
}
}
}
}
public void run(PApplet p){
for(PVector f : food2){
//parent.rectMode(PConstants.CENTER);
parent.ellipseMode(PConstants.CENTER);
parent.stroke(0,food2live);
parent.fill(153,153,0,food2live);
//parent.rect(f.x, f.y, 8, 8);
parent.ellipse(f.x, f.y, 8, 8);
}
}
public void growOld(Food2 f){
ArrayList food2 = f.getFood2();
for(int i = food2.size()-1; i >= 0; i--){
food2live -= 0.06;
}
}
public ArrayList getFood2(){
return food2;
}
public PVector position(){
return position;
}
public boolean rotten(){
if(food2live < 0.0){
return true;
}
else{
return false;
}
}
}
```
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 8:29am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/7 "2018-09-11T08:29:05Z")
how do you define your F2 variable in your first code?
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 8:33am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/8 "2018-09-11T08:33:06Z")
i did not… thats the error right ?
when i run my food2 in the beginning of my code i do that: (but its not connected)
```auto
Iterator F2 = food2.iterator();
while(F2.hasNext()){
Food2 f2 = F2.next();
f2.run(parent);
f2.grow(tree2);
f2.growOld(f2);
if(f2.rotten()){
F2.remove();
}
}
```
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 8:37am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/9 "2018-09-11T08:37:18Z")
And how do you define food2 in the context of your first code?
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 8:42am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/10 "2018-09-11T08:42:46Z")
i dont know what do you mean by that.
here is my code only for food2
```auto
public class World {
ArrayList food2;
public World(PApplet p){
parent = p;
int nombfood2 = 1;
food2 = new ArrayList();
for(int i = 0; i < nombfood2; i++){
food2.add(new Food2(nombfood2, p));
}
}
public void run(){
Iterator F2 = food2.iterator();
while(F2.hasNext()){
Food2 f2 = F2.next();
f2.run(parent);
f2.grow(tree2);
f2.growOld(f2);
if(f2.rotten()){
F2.remove();
}
}
float currentSmallest;
float dist;
for(int a = herb3f.size()-1; a >= 0; a--){
Herbivor3F h3f = herb3f.get(a);
if(h3f.faim() == false){
h3f.randomMv();
}
else{
PVector target = new PVector(0,0);
currentSmallest = (parent.height * parent.height) + (parent.width * parent.width);
do{
Iterator F2f = food2.iterator();
Food2 f = F2f.next();
dist = ((h3f.position.x - f.position.x) * (h3f.position.x - f.position.x)) + ((h3f.position.y - f.position.y) * (h3f.position.y - f.position.y));
if( dist < currentSmallest){
currentSmallest = dist;
target.x = f.position.x;
target.y = f.position.y;
}
}while(F2.hasNext());
h3f.findFood(target);
}
}
}
}
```
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 8:45am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/11 "2018-09-11T08:45:01Z")
sorry for my lack of knowledge.
And i put F2f instead of F2 because its give me an error(duplicate local variable) when i dont change it
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 8:51am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/12 "2018-09-11T08:51:24Z")
> [@vincentstrebelle](#):
>
> sorry for my lack of knowledge
Don’t apologize for that, we have all been there and we all lack of knowledge somewhere 😉
The problem with your last code is that you have already itirated through all of your food with that code:
```auto
while(F2.hasNext()){
Food2 f2 = F2.next();
f2.run(parent);
f2.grow(tree2);
f2.growOld(f2);
if(f2.rotten()){
F2.remove();
}
}
```
So when you do this:
```auto
do{
...
}while(F2.hasNext());
```
You do it only once because it does not have next element anymore.
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 8:54am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/13 "2018-09-11T08:54:55Z")
Try replace that code:
```auto
do{
Iterator F2f = food2.iterator();
Food2 f = F2f.next();
dist = ((h3f.position.x - f.position.x) * (h3f.position.x - f.position.x)) + ((h3f.position.y - f.position.y) * (h3f.position.y - f.position.y));
if( dist < currentSmallest){
currentSmallest = dist;
target.x = f.position.x;
target.y = f.position.y;
}
}while(F2.hasNext());
```
by this one:
```auto
for (Iterator i = food2.iterator (); i.hasNext(); ) {
Food2 f = i.next();
dist = ((h3f.position.x - f.position.x) * (h3f.position.x - f.position.x)) + ((h3f.position.y - f.position.y) * (h3f.position.y - f.position.y));
if( dist < currentSmallest){
currentSmallest = dist;
target.x = f.position.x;
target.y = f.position.y;
}
}
```
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 9:00am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/14 "2018-09-11T09:00:23Z")
i got an error java.lang.NullPointerException on the line :
`dist = ((h3f.position.x - f.position.x) * (h3f.position.x - f.position.x)) + ((h3f.position.y - f.position.y) * (h3f.position.y - f.position.y));`
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 9:01am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/15 "2018-09-11T09:01:40Z")
so my code dont know what is “f” now right ?
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 9:15am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/16 "2018-09-11T09:15:21Z")
when i compare it whit my other behavior (find water) the main difference is thats the food2 appear and disappear so the list change all the time
```auto
float currentSmallest;
float dist;
for(int a = herb3f.size()-1; a >= 0; a--){
Herbivor3F h3f = herb3f.get(a);
if(h3f.soif() == false){
h3f.randomMv();
}
else{
PVector target = new PVector(0,0);
currentSmallest = (parent.height * parent.height) + (parent.width * parent.width);
for(int b = lac.size()-1; b >= 0; b--){
Lac l = lac.get(b);
dist = ((h3f.position.x - l.position.x) * (h3f.position.x - l.position.x)) + ((h3f.position.y - l.position.y) * (h3f.position.y - l.position.y));
if( dist < currentSmallest){
currentSmallest = dist;
target.x = l.position.x;
target.y = l.position.y;
}
}
h3f.findWater(target);
}
}
```
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 9:25am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/17 "2018-09-11T09:25:39Z")
With all the code you posted I don’t know how everything is working together, if this is all the same piece of code or if this is different parts used at different places…
It is really confusing! 🙂
Is it possible to get your full code with some comments around the part that is causing you the issue?
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 9:37am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/18 "2018-09-11T09:37:57Z")
here is my code for the food2 and the herbivor3F is use now:
sorry its a little bit messy
my world class:
```auto
public class World {
PApplet parent;
Tree2 tree2;
ArrayList food2;
ArrayList herb3f;
ArrayList lac;
public World(PApplet p){
parent = p;
int nombtree2 = 20;
tree2 = new Tree2();
for(int i = 0; i < nombtree2; i++){
tree2.add(new PVector(p.random(p.width-1000, p.width-150), p.random(p.height-700, p.height-150)));
}
int nombfood2 = 1;
food2 = new ArrayList();
for(int i = 0; i < nombfood2; i++){
food2.add(new Food2(nombfood2, p));
}
int nombHerb3f = 10;
herb3f = new ArrayList();
for(int i = 0; i < nombHerb3f; i++){
PVector l = new PVector(p.random(p.width),p.random(p.height));
DNA2 dna2 = new DNA2(p);
herb3f.add(new Herbivor3F(l,dna2,p));
}
int nomlac = 3;
lac = new ArrayList();
for(int i = 0; i < nomlac; i++){
PVector l = new PVector(p.random(p.width-1000, p.width-150), p.random(p.height-700, p.height-150));
lac.add(new Lac(p, l));
}
public void run(){
////trees and fruits
tree2.run(parent);
if(parent.random(1) < 0.01){
food2.add(new Food2(0, parent));
}
Iterator F2 = food2.iterator();
while(F2.hasNext()){
Food2 f2 = F2.next();
f2.run(parent);
f2.grow(tree2);
f2.growOld(f2);
if(f2.rotten()){
F2.remove();
}
}
////lac
for(int i = lac.size()-1; i >= 0; i--){
Lac l = lac.get(i);
l.run(parent);
}
////female
Iterator H3F = herb3f.iterator();
while(H3F.hasNext()){
Herbivor3F h3f = H3F.next();
h3f.run(parent);
//h3f.randomMv();
if(h3f.dead()){
H3F.remove();
}
}
for(int a = herb3f.size()-1; a >= 0; a--){
Herbivor3F h3f = herb3f.get(a);
for(int i = food2.size()-1; i >= 0; i--){
Food2 f2 = food2.get(i);
h3f.eat2(f2);
}
}
////drink water
for(int a = herb3f.size()-1; a >= 0; a--){
for(int b = lac.size()-1; b >= 0; b--){
Herbivor3F h3f = herb3f.get(a);
Lac l = lac.get(b);
PVector lpos = l.position;
PVector h3fpos = h3f.position;
float dist = PVector.dist(lpos, h3fpos);
if(h3f.getR() > dist){
h3f.drinkWater();
}
}
}
/*
////find water work great
if(herb3f.size() > 0){
float currentSmallest;
float dist;
for(int a = herb3f.size()-1; a >= 0; a--){
Herbivor3F h3f = herb3f.get(a);
if(h3f.soif() == false){
h3f.randomMv();
}
else{
PVector target = new PVector(0,0);
currentSmallest = (parent.height * parent.height) + (parent.width * parent.width);
for(int b = lac.size()-1; b >= 0; b--){
Lac l = lac.get(b);
dist = ((h3f.position.x - l.position.x) * (h3f.position.x - l.position.x)) + ((h3f.position.y - l.position.y) * (h3f.position.y - l.position.y));
if( dist < currentSmallest){
currentSmallest = dist;
target.x = l.position.x;
target.y = l.position.y;
}
}
h3f.findWater(target);
}
}
}
*/
//////Find food2
float currentSmallest;
float dist;
for(int a = herb3f.size()-1; a >= 0; a--){
Herbivor3F h3f = herb3f.get(a);
if(h3f.faim() == false){
h3f.randomMv();
}
else{
PVector target = new PVector(0,0);
currentSmallest = (parent.height * parent.height) + (parent.width * parent.width);
for(Iterator i = food2.iterator(); i.hasNext();){
Food2 f = i.next();
////here i have my error java null pointer execption//////
dist = ((h3f.position.x - f.position.x) * (h3f.position.x - f.position.x)) + ((h3f.position.y - f.position.y) * (h3f.position.y - f.position.y));
if(dist < currentSmallest){
currentSmallest = dist;
target.x = f.position.x;
target.y = f.position.y;
}
}
h3f.findFood(target);
}
}
}
}
```
my class Food2:
```auto
public class Food2 {
PApplet parent;
ArrayList food2;
ArrayList tree2;
float food2live;
public PVector position;
public Food2(int nombFood2, PApplet p){
parent = p;
food2 = new ArrayList();
food2live = 255;
}
@SuppressWarnings("deprecation")
public void add(PVector l){
food2.add(l.get());
}
public void grow(Tree2 t){
ArrayList tree2 = t.getTree2();
for(int i = 0; i < tree2.size(); i++){
if(parent.random(1) < 0.001){
int nombfood2 = 1;
for(int a = 0; a < nombfood2; a++){
food2.add(new PVector(parent.random(tree2.get(i).x -50, tree2.get(i).x +50), parent.random(tree2.get(i).y-50, tree2.get(i).y +50)));
}
}
}
}
public void run(PApplet p){
for(PVector f : food2){
//parent.rectMode(PConstants.CENTER);
parent.ellipseMode(PConstants.CENTER);
parent.stroke(0,food2live);
parent.fill(153,153,0,food2live);
//parent.rect(f.x, f.y, 8, 8);
parent.ellipse(f.x, f.y, 8, 8);
}
}
public void growOld(Food2 f){
ArrayList food2 = f.getFood2();
for(int i = food2.size()-1; i >= 0; i--){
food2live -= 0.06;
}
}
public ArrayList getFood2(){
return food2;
}
public PVector position(){
return position;
}
public boolean rotten(){
if(food2live < 0.0){
return true;
}
else{
return false;
}
}
}
```
---
### Author:  [@vincentstrebelle](https://discourse.processing.org/u/vincentstrebelle)
#### Post date: [September 11, 2018, 10:15am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/19 "2018-09-11T10:15:47Z")
its too messy or its ok ?
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [September 11, 2018, 11:10am UTC](https://discourse.processing.org/t/problem-with-a-loop/3415/20 "2018-09-11T11:10:23Z")
It makes more sense now, thanks 🙂
Is there a reason why you wouold want to use an iterator?
Why don’t you use the same template as with the water?
Also you never initialize the `position` variable in your Food2 class. I think this is why you get the nullPointerException. It is not because the food does not exists but because position does not exist
```auto
public Food2(int nombFood2, PApplet p){
parent = p;
food2 = new ArrayList();
food2live = 255;
}
```
Also you don’t need this function:
```auto
public PVector position(){
return position;
}
```
That’s because you have set your position variable as public so you can access it directly:
```auto
public PVector position;
```
One last thing: can you explain what this arrayList: `ArrayList<PVector> food2;` is used for? I think you are mixing some things up here.
[Next page](https://discourse.processing.org/t/problem-with-a-loop/3415.md?page=2)