Question

I’m trying to sort an ArrayList by BigDecimal and coming up against a brickwall. I have a class that looks a little like this:

public class deal implements Comparable<deal>{

protected BigDecimal bdPrice;
protected int iQuantity;
protected String sDealType;
protected UUID dealUniqueID;
protected int dealID;
protected BigDecimal bdUnitPrice;

public deal(){
    bdPrice         = new BigDecimal("0");
    bdUnitPrice     = new BigDecimal("0");
    iQuantity       = 1;
    sDealType       = "Single item";
    dealUniqueID    = UUID.randomUUID();
    dealID          = 0;
}

private void setUnitPrice(){
    this.bdUnitPrice = this.bdPrice.divide(new BigDecimal(this.iQuantity));
}

public BigDecimal compareTo(deal oDeal) {
    // TODO Auto-generated method stub
    return bdUnitPrice.compareTo(oDeal.getUnitPrice());
}

public boolean equals(deal oDeal) {
    if (!(oDeal instanceof deal))
        return false;
    deal oD = (deal) oDeal;

    return this.bdUnitPrice.equals(oD.bdUnitPrice);
}
}

and my main Android Activity looks like this:

public class SupermarketDealsActivity extends Activity {
private ArrayAdapter<deal> itemAdapter;
private ListView lvDeals;
private ArrayList<deal> itemArray;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    SetUpView();
}

private void SetUpView(){
lvDeals                     = (ListView)this.findViewById(R.id.listDeals);

    itemArray                   = new ArrayList<deal>();
    itemArray.clear();

    itemAdapter                 = new ArrayAdapter<deal>(this, android.R.layout.simple_list_item_1,itemArray);
    lvDeals.setAdapter(itemAdapter);
}

private void CreateADeal(int iQuantity, BigDecimal bdPrice) {
    deal oDeal                  = new deal();

    oDeal.setQuantity(iQuantity);
    oDeal.setPrice(bdPrice);

    CreateListDeals(oDeal);
}

private void CreateListDeals(deal oDeal){
    itemArray.add(oDeal);
    Collections.sort(itemArray,Collections.reverseOrder());
    itemAdapter.notifyDataSetChanged();
}
}

In my java class I am getting an error with my compareTo method saying:

Type mismatch: cannot convert from int to BigDecimal

I must have missed something along the way, what is it?

Cheers

Answer 1

public BigDecimal compareTo(deal oDeal) {
    // TODO Auto-generated method stub
    return bdUnitPrice.compareTo(oDeal.getUnitPrice());
}

Does not match either the signature of the interface, nor does it match the return type of bdUnitPrice.compareTo. Change it to:

public int compareTo(deal oDeal) {
    // TODO Auto-generated method stub
    return bdUnitPrice.compareTo(oDeal.getUnitPrice());
}

A couple of other things I should mention (from the comments):

1. The names of classes should start with an upper case letter. There is a “code conventions” document that spells out that and other things you should do.
2. You override equals – you should never override equals unless you also override hashCode – otherwise you’ll have tons of problems if you put the objects of this class into a HashSet, HashMap or other collection which uses hash.