Java modify Class element on arraylist

I have two arraylist like this

ArrayList<Paragens> paragens = new ArrayList<Paragens>();
ArrayList<Rotas> rotas = new ArrayList<Rotas>();

Paragens is a class and the constructor is

public Paragens(String nomeParagem) {
    this.nomeParagem = nomeParagem;
    this.existeNaRota = new String[]{"","","","","","","","","","","","","",
    "","","","","","","","","","","","","","","","","","","","","","","","",
    "","","","","","","","","","","","","","","","","","","","","","","","",
    "","","","","","","","","","","","","","","","","","","","","","","",""};
    this.id = contadorParagens++;
}

I have another class. The Rotas class.

public Rotas(String nomeRota, Paragens[] nomeParagens) {
    this.nomeRota = nomeRota;
    this.nomeParagens = nomeParagens;
    this.id = contadorRotas++;
}

So there are Paragens (each one with a name[nomeParagem], an id[contadorParagens] and the rotas in which they exist [existeNaRota].

First, the user inputs Paragens which are only created with nomeParagem(it's name) and its id. Since Rotas are added latter, existeNaRota it's empty.

Each Paragem is then added to paragens arraylist

When user adds an Rotas he inputs Rota name and then the list of Paragens that exist on that Rotas. Rotas are finally added to rotas` arraylist.

What I want to do is, when user insert Paragens that exists on one Rotas, existeNaRota is them populated with the Rotas that Paragemexists.

Example.

User inputs some names and then Paragens are created like this:

paragem = new Paragens("London");
paragens.add(paragem);
paragem = new Paragens("Manchester");
paragens.add(paragem);
paragem = new Paragens("Chelsea");
paragens.add(paragem);

Now user will input Rotas like this:

estacoes[0] = "Chelsea";
estacoes[1] = "London";
rota = new Rotas("Route A", estacoes);
rotas.add(rota);

Now, since there is a Rota I want to go back to Paragens and put the name on existeNaRota.

On Paragens I have this set method

public void setExisteNaRota(String existeNaRota, int indice) {
    this.existeNaRota[indice] = existeNaRota;
    indice++;
}

Is it possible to access the paragens arraylist, find the "Chelsea" Paragem and add "Rota A" to the first position of existeNaRota?

Solution

First, consider using a List in `Paragens' instead of an array since you are going to be adding elements to it. This will allow for adding (potentially to the head of the list) without moving elements in the array.

Second, provide a method in Paragens like addRota(Rota r) that adds the Rota to the List of Rotas in the Paragens.

class Paragens{
   List<Rota> existEnRota = new ArrayList<Rota>();


   public void addRota(Rota r){
       existEnRota.add(0, r);
   }
}