How to create a tree with n children by node? [closed]

  

I'm trying to do this with a ArrayList , but I'm not understanding how to insert a ArrayList within a ArrayList in a recursive or interactive way even though the tree has no defined limit.

This is not what you should do. This is a XY problem .

Java is an object-oriented language. Keeping recursive lists of numbers is not an object-oriented way of attacking your problem. This means that this approach probably will not work. If you can get it to work, the result will be a good gambiarra.

The best way would be to see what objects are involved in this:

Turning these four requirements into code:

public class Arvore {
    private No raiz;
}

import java.util.List;

public class No {
    private int conteudo;
    private List<No> filhos;
}

Ok, now that we have the general structure of our classes, let's define some methods and constructors:

public class Arvore {
    private No raiz;

    public Arvore(int conteudoRaiz) {
        this.raiz = new No(conteudoRaiz);
    }

    public No getRaiz() {
        return raiz;
    }

    public No buscar(int procurado) {
        raiz.buscar(procurado);
    }
}

import java.util.ArrayList;
import java.util.List;

public class No {
    private int conteudo;
    private List<No> filhos;

    public No(int conteudo) {
        this.filhos = new ArrayList<>();
        this.conteudo = conteudo;
    }

    public No acrescentarFilho(int conteudoFilho) {
        No n = new No(conteudoFilho);
        filhos.add(n);
        return n;
    }

    public int getConteudo() {
        return conteudo;
    }

    public List<No> getFilhos() {
        return filhos;
    }

    public No buscar(int procurado) {
        if (procurado == conteudo) return this;
        for (No filho : filhos) {
            No achou = filho.buscar(procurado);
            if (achou != null) return achou;
        }
        return null;
    }
}

You can go adding other methods to accomplish the jobs you want, but the point here is that you have to have well defined what each thing is. Saying that a tree is a list or that a tree node is a list just leaves things complicated and confusing and probably will not work. Ideally, the tree has a root node, that a node has a list of other nodes. Note that the verb is important: the and concept concept completely changes the way you structure your code.