A pathfinding solution

Processing
19

Again, try to move your arrive() methode outside your for loop:

float currentSmallest = (parent.height * parent.height) + (parent.width * parent.width);
float d;

for(int a = carn1m.size()-1; a >= 0; a--){
    Carnivor1M c1m = carn1m.get(a); //Change here
	for(int b = lac.size()-1; b >= 0; b--){
		Lac l = lac.get(b);
		d = ((c1m.position.x - l.position.x) * (c1m.position.x - l.position.x)) + ((c1m.position.y - l.position.y) * (c1m.position.y - l.position.y));
						
		if(d < currentSmallest){
			currentSmallest = d;
			PVector target = new PVector(l.position.x, l.position.y);
		}
	}
    c1m.arrive(target); //And change here
}