trucks

class Trailer {
    private int boxesNr;
    private String matriculationNr;
    private static int last = 10;

    public Trailer(final String matriculationNr) {
        this.matriculationNr = matriculationNr;
        this.boxesNr = ++last;
    }
    public Trailer(final String matriculationNr, int boxesNr) {
        this.matriculationNr = matriculationNr;
        last = this.boxesNr = boxesNr;
    }

    public int getBoxesNr() {
        return boxesNr;
    }

    public String getMatriculationNr() {
        return matriculationNr;
    }

    @Override
    public String toString() {
        return "R(" + matriculationNr + ", " + boxesNr + ")";
    }
}

class Truck {
    private static final int MAX_LEN = 5;
    private Trailer[] trailers;
    private int len;

    public Truck() {
        trailers = new Trailer[MAX_LEN];
        len = 0;
    }

    public boolean addTrailer(final String matriculationNr, int boxesNr) {
        if (len == MAX_LEN) {
            return false;
        }
        trailers[len++] = new Trailer(matriculationNr, boxesNr);
        return true;
    }

    public boolean addTrailer(final Trailer trailer) {
        if (len == MAX_LEN) {
            return false;
        }
        trailers[len++] = trailer;
        return true;
    }

    public Trailer deleteTrailer(final String matriculationNr) {
        Trailer tmp = null;
        int id = -1;
        for (int i = 0; i < len; i++) {
            if (trailers[i].getMatriculationNr().equals(matriculationNr)) {
                tmp = trailers[i];
                id = i;
                break;
            }
        }
        if (id == -1) {
            return null;
        }
        for (int i = id; i < len - 1; i++) {
            trailers[i] = trailers[i + 1];
        }
        len--;
        return tmp;
    }

    private int getTrailersSum() {
        int sum = 0;
        for (int i = 0; i < len; i++) {
            sum += trailers[i].getBoxesNr();
        }
        return sum;
    }

    @Override
    public boolean equals(Object o) {
        if (o instanceof Truck) {
            Truck other = (Truck)o;
            return getTrailersSum() == other.getTrailersSum();
        }
        return false;
    }

    @Override
    public String toString() {
        String string = "T";
        for (int i = 0; i < len; i++) {
            string += " -> " + trailers[i];
        }
        return string;
    }
}

public class Main {
    public static void main(String[] args) {
        Truck truck1 = new Truck(), truck2 = new Truck();
        truck1.addTrailer("1abc", 2);
        truck1.addTrailer("2xyz", 3);
        System.out.println(truck1);
        Trailer trailer = new Trailer("3abc");
        truck2.addTrailer(trailer);
        System.out.println(truck1.equals(truck2));
        truck2.addTrailer("4bfj", 1);
        System.out.println(truck2);
        System.out.println(truck1.equals(truck2));
        truck2.deleteTrailer("3abc");
        System.out.println(truck2);
        System.out.println(truck1.equals(truck2));
    }
}