> The way I did this was:
>
> TypedStructure interface. AbstractTypedStructure class.
> IllegalTypeException exception.
>
> Then TypedSet/List/Map implement Set/List/Map and extend
> AbstractTypedStructure.
Hehehehe...we *could* use dynamic proxy classes to provide
one factory method that would work for all collections and
maps...
This isn't a serious suggestion, just proof that I have way
too much time on my hands...
-Paul
package org.apache.commons.collections;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.HashSet;
public class PredicateCollectionFactory
{
static class PredicateInvocationHandler implements InvocationHandler
{
private Predicate predicate;
private Object target;
public PredicateInvocationHandler(Object target, Predicate
predicate)
{
this.target = target;
this.predicate = predicate;
}
public Object invoke(Object proxy, Method method, Object[]
parameters) throws Throwable
{
if (method.getName().equals("equals"))
{
return defaultInvoke(target, method,
parameters);
}
Class[] types = method.getParameterTypes();
for (int i = 0; i < types.length; i++)
{
if ((types[i] == Object.class) &&
!predicate.evaluate(parameters[i]))
{
throw new
IllegalArgumentException();
}
}
return defaultInvoke(target, method, parameters);
}
static Object defaultInvoke(Object target, Method method,
Object[] parameters) throws Throwable
{
try
{
return method.invoke(target, parameters);
}
catch (InvocationTargetException e)
{
throw e.getTargetException();
}
}
}
private static Class[] getAllInterfaces(Object object)
{
HashSet set = new HashSet();
for (Class c = object.getClass(); c != null; c =
c.getSuperclass())
{
set.addAll(Arrays.asList(c.getInterfaces()));
}
return (Class[])set.toArray(new Class[set.size()]);
}
public static Object create(Object collection, Predicate predicate)
{
InvocationHandler handler = new
PredicateInvocationHandler(collection, predicate);
Class[] interfaces = getAllInterfaces(collection);
ClassLoader loader =
PredicateCollectionFactory.class.getClassLoader();
return Proxy.newProxyInstance(loader, interfaces, handler);
}
// Example usage...
public static void main(String args[])
{
java.util.List list = new java.util.ArrayList();
Predicate predicate = new Predicate() {
public boolean evaluate(Object object)
{
return (object instanceof String);
}
};
list = (java.util.List)create(list, predicate);
list.add("Hello, nurse!"); // works fine
list.add(new Integer(4)); // will raise
IllegalArgumentException
}
}
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