我可以在自己的类中声明一个对象吗？

Question

I'm learning data structures. I have tried to do an exercise to order two stacks with random numbers keeping always them in order from min to max passing comparing and passing the value to another stack called aux . I have a method that fills them in order but I have a problem creating the object aux inside new class. I get the problem <init> . I don't what that means.

PD: After the stacks are in order I pass them to a queue that always has to be in order from max to min.

class Pilas {

    private int max;
    private int[] pila;
    private int tope;

    //Stack constructor
    Pilas(int n) {
        max = n;
        tope = -1;
        pila = new int[max];
    }

    //Method to push a value to stack
    void push(int valor) {
        pila[++tope] = valor;
    }

    //Method to pop a value from stack
    int pop() {
        return pila[tope--];
    }

    //Method to check if the stack is full
    boolean pilaLlena() {
        return tope == max - 1;
    }

    //Method to fill if the stack is empty
    boolean pilaVacia() {
        return tope == -1;
    }

    int seek() {
        return pila[tope];
    }

    **/* The problem that I have
     * Pilas aux= new Pilas(20)
     */**

    //Method to fill stacks in order
    void agregarEnOrden(int valor) {
        if (this.pilaVacia()) this.push(valor);
        else {
            while (valor < this.seek()) {
                aux.push(valor);
            }
            this.push(valor);
            while (!aux.pilaVacia()) {
                this.push(aux.pop());
            }
        }
    }
}

//Queue class
class FilaEstaticas {

    private int ar[];
    private int max;
    private int fin;

    //Queue constructor 
    FilaEstaticas(int t) {
        max = t;
        fin = -1;
        ar = new int[max];
    }

    //Method to check if the queue is empty
    boolean FilaEstaticaVacia() {
        return fin == -1;
    }

    //Method to check if the queue is full
    boolean FilaEstaticaLlena() {
        return fin == max - 1;
    }

    //Method to add a value to queue
    void agregar(int valor) {
        ar[++fin] = valor;
    }

    //Method to remove a value from queue
    int quitar() {
        int dato = ar[0];
        fin--;
        flota();
        return dato;
    }

    //method to move the position after removing a
void flota() {
        for(int i = 0; i <= fin; i++)
            ar[i] = ar[i + 1];
    }
}

class LaboratorioEstaticas {

    public static void main(String args[]) {
        int max = 10;
        FilaEstaticas fila = new FilaEstaticas(2 * max);
        Pilas p1 = new Pilas(10);
        Pilas p2 = new Pilas(10);
        int numero;

        while (!p1.pilaLlena()) {
            numero = (int)(Math.random() * 100);
            System.out.println("Numero agregado a la Pila " + numero);
            p1.agregarEnOrden(numero);
        }

        while (!p2.pilaLlena()) {
            numero = (int)(Math.random() * 100);
            System.out.println("Numero agregado a la Pila " + numero);
            p2.agregarEnOrden(numero);
        }

        while (!p1.pilaVacia() && !p2.pilaVacia()) {
            if (p1.seek() > p2.seek()) fila.agregar(p1.pop());
            else fila.agregar(p2.pop());

            if (p1.pilaVacia()) {
                while (!p2.pilaVacia()) {
                    fila.agregar(p2.pop());
                }
            } else {
                while (!p1.pilaVacia()) {
                    fila.agregar(p1.pop());
                }
            }
        }

        while (!fila.FilaEstaticaVacia()) {
            System.out.println(fila.quitar());
        }
    }
}

Answer 1

This answer thread discusses the problem in detail.
When is it ok to create object of a class inside a method of that class?