Re: Force implementation of equals() and hashCode()?

From:

Tom Anderson <twic@urchin.earth.li>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 2 Oct 2008 13:21:02 +0100

Message-ID:

<Pine.LNX.4.64.0810021316250.31397@urchin.earth.li>

On Wed, 1 Oct 2008, Mike Schilling wrote:

Chris wrote:

Is there any way to force a class that implements an interface to
implement both equals() and hashCode()?

I want all classes that implement a certain interface to work properly
in a HashMap. This means they need to implement their own version of
equals() and hashCode(). Trouble is, if I add those methods to the
interface, the system doesn't squawk if the class doesn't implement
them, because it just inherits them from Object.

I'm not sure what you're getting at, since the default versions of
equals() and hashCode() work fine in HashMaps.

class AccountIdentity {
private int accountNumber ;
private int sortCode ;
public AccountIdentity(int accountNumber, int sortCode) {
this.accountNumber = accountNumber ;
this.sortCode = sortCode ;
}
}

class Account {
}

Map<AccountIdentity, Account> accounts = new HashMap<AccountIdentity, Account>() ;
int acNo = 34509871 ;
int sort = 89273 ;
accounts.put(new AccountIdentity(acNo, sort), new Account()) ;
Account acc = accounts.get(new AccountIdentity(acNo, sort)) ;
assert acc != null ;

tom

--
What we're dealing with here is a complete lack of respect for the law. --
Buford T. Justice