I'm a Java beginner and I'm currently working on a project that I have almost completed.

I need to remove, modify and extract elements of a list (it's a basic one, though I know there are arrayList(s).) This is driving myself crazy, because I know exactly what I need to do, but I'm not getting what should I need start programming.

```
package lec05;

import java.util.*;

/**
 *
 * @author ulacit
 */
public class Lista {

Celda head;

public Lista() {
    head = null;
}

public void add(Person aPerson) {
    if (head == null) {  // list = empty
        head = new Celda(aPerson);
    } else if (aPerson.getId() < head.getInfo().getId()) {  // add element - left
        Celda aux = new Celda(aPerson);
        aux.setNext(head);
        head = aux;
    } else if (head.getNext() == null) {  // add 1 element - right
        Celda aux = new Celda(aPerson);
        head.setNext(aux);
    } else { // more than 1 - add at the end or in the middle
        Celda actual = head;
        while (actual.getNext() != null
                && actual.getNext().getInfo().getId() < aPerson.getId()) {
            actual = actual.getNext();
        }
        Celda aux = new Celda(aPerson);
        aux.setNext(actual.getNext());
        actual.setNext(aux);
    }
}

public boolean (int id) {
    Celda aux = head;
    while (aux != null && aux.getInfo().getId() < id) {
        aux = aux.getNext();
    }
    return (aux != null && aux.getInfo().getId() == id);
}

public Person restore(int id) {
    Celda aux = head;
    while (aux != null && aux.getInfo().getId() < id) {
        aux = aux.getNext();
    }
    if (aux != null && aux.getInfo().getId() == id) {
        return aux.getInfo();
    } else {
        return null;
    }
}

public void remove(int id) {

}

public void modify(int id, String name) {

}
public Persona extract(int id) {
}

@Override
public String toString() {
    String s = "List{";
    Celda aux = head;
    while (aux != null) {
        s += aux.getInfo() + ", ";
        aux = aux.getNext();
    }
    return s;

}
}

```