Re: Java.lang.NoSuchMethodException
"ramakrishna" wrote...
can any one tell me, why NoSuchMethodException will come in
Class.getConstructor( Class[] parameterTypes) method.
In my program Iam using the one constructor and iam calling the
constructor by passing array of class object
I believe I have already answered your question once...
[snipped a lot of code]
As iam feeling that it does not accept the SubClass object.
1. Is there any difference b/w "new" and reflection package
creation object.
When using "new" the JVM looks for the "best case" constructor, i.e. if
there is no constructor with *exactly* the type of the argument, it looks
for constructors where polymorphism can be used, i.e. if there are any
constructors that can take a supertype of the parameters.
When using reflection to get a constructor, you need to provide the
*declared* parametertypes. There you provide/get instances of "Class", but a
Class-instance of a subtype is not polymorph to a Class-instance of a
supertype.
You need to search through the constructors yourself, to see which of them
that has the "best fit".
Here's a quick fix you could use to get such a Constructor:
--------------------------------------------
public static Constructor getPossibleConstructor
(Class motherClass, Class[] pars) {
Constructor[] ctors = motherClass.getConstructors();
for (Constructor c : ctors) {
Class[] cpars = c.getParameterTypes();
if (cpars.length != pars.length) continue;
boolean found = true;
for (int i = 0; i < cpars.length; ++i) {
if (!cpars[i].isAssignableFrom(pars[i])) {
found = false;
break;
}
}
if (found) return c;
}
return null;
}
--------------------------------------------
Now, using the names you've used in previous posts, you could:
--------------------------------------------
....
Class[] tParameterClasses = new Class[1];
tParameterClasses[0] = gauUnau.getClass();
Class tClass = Class.forName( ActionHelper );
// using the method provided above...
// though it also should have a check for null
// in case no constructors can fit with the
// provided parameter classes...
Constructor tConstructor =
getPossibleConstructor(tClass, tParameterClasses);
Object[] tParameterObjects = new Object[1];
tParameterObjects[0] = (Object) gauUnau;
ActionHelper actionHelper =
(ActionHelper)
tConstructor.newInstance(tParameterObjects);
// Bjorn A
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