Crash at Run-Time

Question

class Nota{
    public int getLength(){
        return length;
    public String getName(){
        return name;
    public Nota(String name, int length){
        this.name=name;
        if ((length==1) || (length==2) || (length==4))
            this.length=length;
        else throw new RuntimeException();
    public boolean equals(Object n){
        if (this==n) return true;
        if (n==null) return false;
        if (!(n instanceof Nota)) return false;
        Nota note=(Nota) n;
        return name.equals(note.getName());
    private String name;
    private int length;
class Spartito implements Iterable<Set<Nota>>{
    public void add(Nota note, int starTime){
        class Accordo extends HashSet<Nota>{
            public String toString(){
                Iterator<Nota> i=super.iterator();
                String res=((Nota)i.next()).getName();
                while (i.hasNext())
                    res+=", "+((Nota)i.next()).getName();
                    return res;
        for (int i=0; i<starTime; i++){
            try{
                timeLine.get(i);
            }catch(IndexOutOfBoundsException e){
                timeLine.set(i,new Accordo());
        int endTime=starTime+note.getLength();
        for (int i=starTime; i<endTime; i++){
            try{
                timeLine.get(i).add(note);
            }catch(IndexOutOfBoundsException e){
                Accordo accordo=new Accordo();
                accordo.add(note);
                timeLine.set(i,accordo);
    public Iterator<Set<Nota>> iterator(){
        return timeLine.iterator();
    public Spartito(){
        ArrayList<Set<Nota>> timeLine=new ArrayList<Set<Nota>>();
    private ArrayList<Set<Nota>> timeLine;
}use case:
public static void main(String[] x){
        Spartito fuga=new Spartito();
        fuga.add(new Nota("Do", 4), 0);
        fuga.add(new Nota("Mi", 1), 0);
        fuga.add(new Nota("Mib", 2), 1);
        fuga.add(new Nota("Sol", 2), 2);
        for (Set<Nota> accordo : fuga)
            System.out.println(accordo);
Error at Run-Time:
Exception in thread "main" java.lang.NullPointerException
     at Spartito.add(Es3.java:69)
     at Es3.main(Es3.java:6)
Class Nota is a musical note. The class Spartito represents musical tabs. Each note specifies a duration in units of time, so a Spartito becomes a time sequence of musical arrangements. I need to run software with the specified use case.
Edited by: ungoro on Apr 3, 2009 7:27 AM

Answer 1

no problem, if i posted on this forum then it means that i need help...
a concept that i cannot explain is that i need to manage any possible breaks (pauses) in the Spartito. To understand us better, take this use case:
    public static void main(String[] x){
        Spartito fuga=new Spartito();
        fuga.add(new Nota("Do", 4), 0);
        fuga.add(new Nota("Mi", 1), 0);
        fuga.add(new Nota("Mib", 2), 1);
        fuga.add(new Nota("Sol", 2), 8);
        for (Set<Nota> accordo : fuga)
            System.out.println(accordo);
    }from second 5 to 8 there aren't any note into the Spartito, then at 9th second cames a Sol. I expect an output that look like this:
Do, Mi
Do, Mib
Do, Mib
Do
<<pause>>
<<pause>>
<<pause>>
<<pause>>
Sol
Sol
However your suggestions are valid, and i wellcome them all.
The result (for now!) is the following code:
class Nota{
    public int getLength(){
        return length;
    public String getName(){
        return name;
    public Nota(String name, int length){
        this.name=name;
        if ((length==1) || (length==2) || (length==4))
            this.length=length;
        else throw new IllegalArgumentException("Invalid length: "+length);
    public boolean equals(Object n){
        if (this==n) return true;
        if (n==null) return false;
        if (!(n instanceof Nota)) return false;
        Nota note=(Nota) n;
        return name.equals(note.getName());
    private String name;
    private int length;
    public static final Nota PAUSA=new Nota("<<pause>>",1);
class Spartito implements Iterable<Set<Nota>>{
    public void add(Nota note, int starTime){
        class Accordo extends TreeSet<Nota>{
            public String toString(){
                Iterator<Nota> i=super.iterator();
                if (!(i.hasNext())) return "";
                String res=((Nota)i.next()).getName();
                while (i.hasNext())
                    res+=", "+((Nota)i.next()).getName();
                return res;
            public Accordo(){
                super(
                    new Comparator<Nota>(){
                        public int compare(Nota n1,Nota n2){
                            return n1.getName().compareTo(n2.getName());
        for (int i=timeLine.size(); i<starTime; i++){
            Accordo accordo=new Accordo();
            timeLine.add(i,accordo);
            accordo.add(Nota.PAUSA);
        int endTime=starTime+note.getLength();
        for (int i=starTime; i<endTime; i++){
            Set<Nota> accordo;
            if (i<timeLine.size()){
                accordo=timeLine.get(i);
                accordo.remove(Nota.PAUSA);
            }else{
                accordo=new Accordo();
                timeLine.add(i,accordo);
            accordo.add(note);
    public Iterator<Set<Nota>> iterator(){
        return timeLine.iterator();
    public Spartito(){
        timeLine=new ArrayList<Set<Nota>>();
    private ArrayList<Set<Nota>> timeLine;
}