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

From:
Tom Anderson <twic@urchin.earth.li>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 3 Oct 2008 00:12:02 +0100
Message-ID:
<Pine.LNX.4.64.0810030007400.26249@urchin.earth.li>
On Thu, 2 Oct 2008, Mike Schilling wrote:

Tom Anderson wrote:

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 ;


Yes, it's possible that the OP meant "I want value semantics, not
reference semantics", but he didn't say so.


No, but i bet you a million dollars in collateralized debt obligations
that that's what he was getting at. Since when did people posting
questions in this group fully explain what they needed?

tom

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