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Subject: RE: Modify getter result
Date: Mon, 20 Dec 2004 21:38:06 -0500
Message-ID: <8E2D018A78A5A04095667ADF098FF29A03DEAFC2@ms06>
Thread-Topic: Modify getter result
Thread-Index: AcTmnV/DXXWu2tVdRfqJkH0LKHoG4wAZx/cg
From: "Tim O'Brien" <tobrien@discursive.com>
To: "Jakarta Commons Users List" <commons-user@jakarta.apache.org>

Stephen already responded, but here is the code you would need:

import org.apache.commons.collections.Factory;
import org.apache.commons.collections.functors.ConstantFactory;
import org.apache.commons.collections.map.LazyMap;
Import java.util.*;

 Map currency =3D new HashMap()
 {
 	{
 		put("DE", "EUR");
 		put("US", "USD");
 	}
 };

 Factory factory =3D new ConstantFactory("XY");
 Map lazy =3D Lazy.map(currency, factory);

 String blah =3D (String) lazy.get("XY");=20


ConstantFactory is just a factory which returns a constant Object, in
this case a request for "XY" would return the default value.

If you wanted to add your logging code, you could do this instead:

Factory factory =3D new Factory() {
	public Object create() {
		// logging stuff goes here....
		return "default";
	}
}

But, you should know that after you get "XY", the Map will then contain
"XY" as a key.  If you wanted do this without side-effects (i.e. without
adding a value to the Map), you could mess around with decorating the
original Map with the FixedSizeMap, but the problem here is that adding
a new key will throw IllegalArgumentException.

Tim O'Brien

> -----Original Message-----
> From: Nentwig, Timo [mailto:timo.nentwig@jamba-ag.de]=20
> Sent: Monday, December 20, 2004 8:08 AM
> To: commons-user@jakarta.apache.org
> Subject: Modify getter result
>=20
> Hi!
>=20
> I'm not sure whether this can be done with commons-collections.=20
>=20
> I need to hook in a collection and return a default value=20
> when the requested key does not exist in the collection. E.g.
>=20
> Map currency =3D new HashMap()
> {
> 	{
> 		put("DE", "EUR");
> 		put("US", "USD");
> 	}
> };
>=20
> And currency.get("XY") is supposed to return a default value=20
> (this may require additional logic and e.g. may write to the=20
> logger that an yet unsupported ISOCODE was requested).
>=20
> Can this be done?
>=20
> Kind regards
> Timo
>=20
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>=20
>=20
>=20

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