How do I get data from a 2D array with this method?

Question

I have been given a method that returns a two dimensional object array. How can I get the data from the object array using the method given below, and put in a table or label to view the data that is stored within? This is what I have tried with no success:

Object[][] diffs = comp.getDifferences(comp.getName());
for(Object diff : diffs){

    table.addItem(diff);
}

This is the method I was given:

public Object[][] getDifferences(String table) {
    List<Tuple<Object, Object>> difference = differences.get(table);
    Object[][] array = new Object[difference.size()][2];

    for (int i = 0; i < array.length; i++) {
        array[i][0] = difference.get(i).item1();
        array[i][1] = difference.get(i).item2();
    }

    return array;
}

Any suggestions?

UPDATE: 3:52 CST 3/17:

I've come up with this...

    Table table = new Table();      
    Object[][] diffs = comp.getDifferences(comp.getName());
    for(int i = 0; i < diffs.length; i++){          
        table.addItem(diffs[i][0]);
        table.addItem(diffs[i][1]);
    }

This also isn't working. I get an NPE that points to this line:

Object[][] array = new Object[difference.size()][2];

Here is the entire Compare(comp) class:

public class Compare implements Serializable {
private String name;
private Map<String, List<Tuple<Object, Object>>> differences = new HashMap<String, List<Tuple<Object, Object>>>();

public Compare(String name) {
    this.name = name;
}

public Compare(byte[] bytes) throws IOException, ClassNotFoundException {
    ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
    ObjectInput ois = new ObjectInputStream(bis);

    Compare compare = (Compare)ois.readObject();
    this.name = compare.name;
    this.differences = compare.differences;

    bis.close();
    ois.close();
}

public String getName() {
    return name;
}

public boolean addDifference(String table, Object control, Object test) {
    if (!differences.containsKey(table)) {
        differences.put(table, new ArrayList<Tuple<Object, Object>>());
    }

    differences.get(table).add(new Tuple<Object, Object>(control, test));

    return true;
}

public Object[][] getDifferences(String table) {
    List<Tuple<Object, Object>> difference = differences.get(table);
    Object[][] array = new Object[difference.size()][2];

    for (int i = 0; i < array.length; i++) {
        array[i][0] = difference.get(i).item1();
        array[i][1] = difference.get(i).item2();
    }

    return array;
}

public byte[] toBytes() throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ObjectOutput oos = new ObjectOutputStream(bos);

    oos.writeObject(this);
    oos.flush();

    byte[] bytes = bos.toByteArray();

    bos.close();
    oos.close();

    return bytes;
}

private class Tuple<X, Y> implements Serializable {
    private final X x;
    private final Y y;

    public Tuple(X x, Y y) {
        this.x = x;
        this.y = y;
    }

    public X item1() {
        return this.x;
    }

    public Y item2() {
        return this.y;
    }
}

public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
    Compare foo = new Compare("Test Compare");
    foo.addDifference("AGREEMENT", 89, 90);
    foo.addDifference("AGREEMENT", "foo", "bar");
    foo.addDifference("ACCOUNT", 123, "Dog");

    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(new File("C:\\Users\\uttbm01\\Documents\\Export\\foo.cmp")));
    oos.writeObject(foo);
    oos.close();

    ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("C:\\Users\\uttbm01\\Documents\\Export\\foo.cmp")));
    Compare bar = (Compare)ois.readObject();
    ois.close();

    System.out.println();
}

}

Answer 1

I am not going through all of your code. The reason I can see why you get a NullPointerException in the line you say is that in difference.size() difference is null, so you are calling a method on a null. This in turn is most likely because the map I inquired about, differences, does not have a mapping with your table as a key (the less likely explanation is that the key is there, but the value associated with it is null).

If you are sure the key-value pair should be there (with a non-null value), you need to go through the code that put it in there to see why it didn’t. If on the other hand you don’t want to guarantee it’s there, you should do a null check on difference with an if-else. If difference is null, you may for example return new Object[0][] from your method.