Method -help

Question

Hi!
There are two classes: CDRack and Record(which is done).
I have problems with methods
-getNumberOfCDs()
Should I write a new field numberOfCDs, or do I get it in other way?
-ideas how to accomplish
method move(CDRack anotherRack) ?
thanks a lot!
ps.How can I put Duke Dollars to my question? I`ve searched
information but haven't found.
Class CDRack represents collections of compact discs. Discs are located
in the rack in slots numbered from zero upwards. The discs are
represented by Record objects and empty slots by null values.
public class CDRack extends Object {
  private Record[] collection;
  private int size;
  private Record record;
  private int slot;
/** Creates a new, empty CD rack.
Parameters:
size - the size of the new rack, i.e. the number of slots it has */
    public CDRack(int size) {
      collection = new Record[size];
      this.size = size;
      this.slot = slot;
Returns the size of the rack, i.e. the number of slots it has.
Returns:
the size of the rack
    public int getSize() {
      return this.size;
/** Returns the number of CDs in the rack.
Returns:
the number of discs in the rack
    public int getNumberOfCDs() {
Returns the cd in the given rack slot.
Parameters:
slot - a slot number
Returns:
the cd in the given slot or null if the slot is empty
    public Record getCD(int slot) {
      if (collection[slot].equals(null) )
         return null;
      else {
         record = collection[slot];
         return record;
/** Inserts a cd in the given rack slot if the slot in question is empty.
Parameters:
disc - the cd to be added in the rack
slot - the number of a (hopefully empty) slot
Returns:
a boolean value indicating if the insertion was successful. */
    public boolean insert(Record disc,
                          int slot) {
      if (collection[slot].equals(null)) {
         collection[slot] = record;
         return true;
      else
         return false;
/** Removes a CD from the given rack slot.
Parameters:
slot - the slot to be emptied
Returns:
the removed cd or null if the given slot was empty */
    public Record remove(int slot) {
      if (collection[slot].equals(null))
         return null;
      else {
         record = collection[slot];
            collection[slot] = null;
            return record;
/** Determines if the given disc object is stored in the rack.
Parameters: disc - a disc to be located in the rack
Returns:
the slot number of the given cd if it is in the rack or a negative number if it is not */
    public int find(Record disc) {
      if (collection[slot].equals(null))
             return -1;
      else {
         record = collection[slot];
         return slot;
/** Inserts the given cd in the first empty rack slot (if there is even
one empty slot in the rack).
Parameters: disc - the disc to be added in the rack
Returns:
the number of the slot where the disc was added, or a negative number
if the rack was already full */
    public int insert(Record disc) {
      if (collection[slot].equals(null)) {
         record = collection[slot];  
         return slot;
      else  
         return -1;
/** Moves all the discs from the given cd rack to this rack. The cds from the
other rack are inserted in the empty slots of this rack (in ascending numerical
order of slot numbers) in the order in which they are located in the other rack.
The moved discs are removed from their original rack. Even if there is not enough space
for all the discs in this rack, as many cds are moved as possible.
Parameters:
anotherRack - another rack whose cds are to be moved into this one
Returns:
the number of cds moved from the other rack to this one */
    public int move(CDRack anotherRack) {
In another class Record I have
-constructor Record(String artist, String name, String category), which
creates a new record with the given properties.
and methods:
-String getArtist() Returns the name of the artist.
-String getCategory() Returns the category in which the recording has been pigeonholed.
-String getName() Returns the name of the record

Answer 1

public int getNumberOfCDs() {
    int count = 0;
    for (int c=0; c<collection.length; c++) {
       if (collection[c]!=null) {
          count++;
    return count;
public int insert(Record disc) {
    for (int c=0; c<collection.length; c++) {
        if (collection[c]!=null) {
            collection[c] = disk;
            return c;
    return -1; // not enough place
public int move(CDRack anotherRack) {
    for (int c=0; c<collection.length; c++) {
        if (collection[c]!=null) {
           if (anotherRack.insert(collection[c])<0) {
               throw new RuntimeException("no more empty slot");
           } else {
               collection[c] = null;
}Btw, you don't really need such members as "slot", "record", "size".