src_Ferry.java

import java.util.ArrayList;

public class Ferry {
    private String regNumber;   // Matricula del ferry
    private String name;        // Nom del ferry
    private String harbourName; // Nom del port destí del ferry
    private double pricePerAxle;// Preu en € que cobra el ferry al camió per cada eix
    private double pricePerTon; // Preu en € que cobra el ferry al camió per cada Tm de pes
    private double maxWeight;   // Pes màxim en Tm dels camions transportables pel ferry.
    private ArrayList<Lorry> boardedLorries; // Els camions carregats al ferry

    public Ferry() {

    }
    public Ferry(String regNumber) {
        this(regNumber, "Barcaza", "Puerto Pobre", 25, 15, 200);
    }
    public Ferry(String regNumber, String name, String harbourName, double pricePerAxle, double pricePerTon, double maxWeight) {
        this.regNumber = regNumber;
        this.name = name;
        this.harbourName = harbourName;
        this.pricePerAxle = pricePerAxle;
        this.pricePerTon = pricePerTon;
        this.maxWeight = maxWeight;
        boardedLorries = new ArrayList<>();
    }

    public double totalWeight() {
        int tmp=0;
        for (int i = 0; i < boardedLorries.size(); i++) {
            tmp+=boardedLorries.get(i).getWeight();
        }
        return tmp;
    }
    public boolean isBoarded(Lorry lorry) {
        return boardedLorries.contains(lorry);
    }
    public boolean canBoard(Lorry lorry) {
        if (lorry.getWeight() > maxWeight || isBoarded(lorry)) return false;
        return true;
    }
    public boolean board(Lorry lorry) {
        if (!canBoard(lorry))
            return false;
        boardedLorries.add(lorry);
        return true;
    }
    public Lorry lorryInPosition(int n){
        return boardedLorries.get(n);
    }
    public double tollPrice(Lorry lorry) {
        return (pricePerAxle*lorry.getNAxles()+pricePerTon*lorry.getWeight());
    }
    public double collectedTolls() {
        double tmp=0;
        for (int i = 0; i < boardedLorries.size(); i++) {
            tmp+=tollPrice(boardedLorries.get(i));
        }
        return tmp;
    }
    @Override
    public boolean equals (Object o) {
        if (this == o) return true;
        if (o == null ) return false;

        Ferry ferry = (Ferry) o;

        return regNumber.equals(ferry.regNumber);
    }
    @Override
    public int hashCode() {
        return regNumber.hashCode();
    }

    public static void main(String[] args) {
        Ferry f = new Ferry("CKB-9875645", "Titanic", "Port de Barcelona", 25, 6, 20);

        Lorry[] l = new Lorry[5];
        l[0]=new Lorry("1234ABC", 11, 2);
        l[1]=new Lorry("4578CPS", 15, 2);
        l[2]=new Lorry("7894JKI", 20, 3);
        l[3]=new Lorry("6824BOE", 25, 3);
        l[4]=new Lorry("5769AAZ", 30, 5);

        for (Lorry i: l) {
            if (f.board(i)) System.out.println("EMBARCAT: "+i.toString());
            else System.out.println("NO EMBARCAT: "+i.toString());
        }
        System.out.println();
        for (Lorry i: l) {
            if (f.isBoarded(i)) System.out.println("ESTA EMBARCAT: " + i.toString());
            else System.out.println("NO esta embarcat: "+i.toString());
        }

        System.out.println("Total recaptat: "+f.collectedTolls()+"€");
    }
}

src_Lorry.java

/**
 * Created by Charly on 3/10/16.
 */
public class Lorry {
    private String regNumber;   // La matrícula del camió.
    private double weight;      // El pes del camió en Tm.
    private int nAxles;         // El nombre d'eixos del camió.

    public Lorry() {

    }
    public Lorry(String regNumber) {
        this(regNumber, 25, 6);
    }
    public Lorry(String regNumber, double weight, int nAxles) {
        this.regNumber=regNumber;
        this.weight=weight;
        this.nAxles=nAxles;
    }


    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null ) return false;

        Lorry lorry = (Lorry) o;

        return regNumber.equals(lorry.regNumber);
    }
    @Override
    public int hashCode() {
        return regNumber.hashCode();
    }
    public int getNAxles() {
        return nAxles;
    }
    public double getWeight() {
        return weight;
    }
    public String toString() {
        return "regNumber:" +regNumber+", weight:"+weight+", nAxles:"+nAxles;
    }
}