/*
* JMEP - Java Mathematical Expression Parser.
* Copyright (C) 1999 Jo Desmet
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* You can contact the Original submitter of this library by
* email at: Jo_Desmet@yahoo.com.
*
*/
package com.iabcinc.jmep.hooks;
/**
* Interface that defines a skeleton for a Unit call-back adaptor.
* It should be implemented in order to use it with the addUnit method
* of Environment. A way to accomplish this is by using in-line adaptor
* classes:<p>
*<ul><pre><code>Environment oEnv = new Environment();
*oEnv.addUnit("mm",new Unit() {
* apply(Object oValue) {
* if (oValue instanceof Double)
* return new Double(0.001*((Double)oValue).doubleValue());
* if (oValue instanceof Integer)
* return new Double(0.001*((Integer)oValue).intValue());
* return null;
* }
*});
* </code></pre></ul>
*
* @see com.iabcinc.jmep.Environment
*/
public interface Unit {
/**
* Defines the unit's behaviour. This method is expected to
* check the arguments validity, and in case of any problems (unsupported
* argument type) it should return <code>null</code>.
* @param oValue the argument on which the the unit will perform an action
* @return the result after applying the unit, <code>null</code> in case of problems.
* Supported return types are: <code>String</code>, <code>Integer</code> and <code>Double</code>.
*/
public Object apply(Object oValue);
}