> For the complete documentation index, see [llms.txt](https://educacion.gitbook.io/programacion/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://educacion.gitbook.io/programacion/exercicios-java/ud6-solucions/pilas.md).

# Pilas

1. Clase Pila

```java
package Listas;

public class Nodo<E> {
    private E elemento;
    private Nodo siguiente;

    public Nodo(E elemento) {
        this.elemento = elemento;
        this.siguiente = null;
    }

    public E getElemento() {
        return elemento;
    }

    public void setElemento(E elemento) {
        this.elemento = elemento;
    }

    public Nodo getSiguiente() {
        return siguiente;
    }

    public void setSiguiente(Nodo siguiente) {
        this.siguiente = siguiente;
    }

    @Override
    public String toString() {
        return "Nodo{" +
                "elemento=" + elemento +
                '}';
    }
}
```

```java
public class Pila<E> {

    private Nodo<E> cima;
    private int tamano;

    public Pila() {
        this.cima = null;
        this.tamano = 0;
    }

    // Engade un elemento á parte superior
    public void push(E elemento) {
        Nodo<E> novoNodo = new Nodo<>(elemento);
        if (cima != null) {
            novoNodo.setSiguiente(cima);
        }
        cima = novoNodo;
        tamano++;
    }

    // Retira e devolve o elemento da cima
    public E pop() {
        if (isEmpty()) {
            return null; 
        }
        E elemento = cima.getElemento();
        cima = cima.getSiguiente();
        tamano--;
        return elemento;
    }

    // Mira o elemento da cima sen retiralo
    public E peek() {
        if (isEmpty()) {
            return null;
        }
        return cima.getElemento();
    }

    // Devolve o número de elementos
    public int size() {
        return tamano;
    }

    // Comproba se a pila está baleira (O que che faltaba!)
    public boolean isEmpty() {
        return cima == null;
    }
    
    @Override
    public String toString() {
        if (isEmpty()) {
            return "Pila baleira";
        }
    
        StringBuilder sb = new StringBuilder();
        sb.append("PILA{");
        
        Nodo<E> actual = cima;
        while (actual != null) {
            sb.append("[ ").append(actual.getElemento()).append(" ]\n");
            actual = actual.getSiguiente();
        }
        sb.append(" }");
        
        return sb.toString();
    }
}
```

```java
package Pilas;

import javax.swing.*;
import java.awt.*;

public class Navegador extends JFrame {

    private JPanel panSup, panCent, panInf;
    private JLabel campoURL, webActual, pilaHistorial;
    private JTextField nuevaURL;
    private JButton anadir, atras;

    public Navegador(){
        // Configuración da ventá
        setTitle("Simulador de Historial");
        setSize(400, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        this.campoURL = new JLabel("URL:");
        this.nuevaURL = new JTextField("Introduzca una web");
        this.nuevaURL.setPreferredSize(new Dimension(80,20));
        this.webActual = new JLabel("Pagina de inicio");
        this.webActual.setFont(new Font("Arial", Font.BOLD, 16));
        this.pilaHistorial = new JLabel("Pila[]");
        this.anadir = new JButton("Visitar");
        this.atras = new JButton("Atrás");


        this.panSup = new JPanel();
        this.panSup.setLayout(new FlowLayout());
        this.panSup.setSize(new Dimension(400,50));
        this.panSup.add(campoURL);
        this.panSup.add(nuevaURL);

        this.panCent = new JPanel(new GridLayout(2,1));
        this.panCent.add(webActual);
        this.panCent.add(pilaHistorial);

        this.panInf = new JPanel();
        this.panInf.setLayout(new FlowLayout());
        this.panInf.setSize(new Dimension(400,50));
        this.panInf.add(atras);
        this.panInf.add(anadir);


        this.add(panSup, BorderLayout.NORTH);
        this.add(panCent, BorderLayout.CENTER);
        this.add(panInf, BorderLayout.SOUTH);

        this.setVisible(true);


    }

    public JPanel getPanSup() {
        return panSup;
    }

    public JPanel getPanCent() {
        return panCent;
    }

    public JPanel getPanInf() {
        return panInf;
    }

    public JLabel getCampoURL() {
        return campoURL;
    }

    public JLabel getWebActual() {
        return webActual;
    }

    public JTextField getNuevaURL() {
        return nuevaURL;
    }

    public JButton getAnadir() {
        return anadir;
    }

    public JButton getAtras() {
        return atras;
    }

    public JLabel getPilaHistorial() {
        return pilaHistorial;
    }
}

```

```java
 package Pilas;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Controlador {

    private Navegador navegador;
    private Pila<String> pila;

    public Controlador(Navegador n, Pila<String> pilaHistorial){
        this.navegador = n;
        this.pila = pilaHistorial;

        this.navegador.getAnadir().addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String url = navegador.getNuevaURL().getText();
                if (!url.isEmpty()){
                    pila.push(url);
                    navegador.getWebActual().setText(url);
                    navegador.getNuevaURL().setText("");
                    navegador.getPilaHistorial().setText(pila.toString());
                }
            }
        });

        this.navegador.getAtras().addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (!pila.isEmpty()){
                    String anterior = pila.pop();
                    navegador.getWebActual().setText(anterior);
                    navegador.getPilaHistorial().setText(pila.toString());
                }
            }
        });

    }


}

```

```java
package Pilas;

import ClasesAbstractas.dispositivos.Conectable;

public class App {

    public static void main(String[] args) {
        Navegador navegador = new Navegador();
        Pila<String> pila = new Pila<>();
        Controlador cont = new Controlador(navegador,pila);
    }
}

```


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