Question

I am trying to create new instances of a class (specifically a subclass of an abstract class) by using the forName(String) method.

For example, if I wanted a subclass of Number:

import static java.lang.Class.forName;
import java.lang.reflect.Constructor;

Object[] arguments = new Object[] {0};
String classname = "java.lang.Integer";
try {
 Class<? extends Number> c = forName(classname).asSubclass(Number.class);
 Constructor<? extends Number> constructor = c.getConstructor(Number.class);
 Number x = constructor.newInstance(arguments);
}
catch (Exception e) {
 e.printStackTrace();
}

What am I doing wrong?

EDIT: Stacktrace

java.lang.NoSuchMethodException: 
java.lang.Integer.<init>(java.lang.Number)
at java.lang.Class.getConstructor0(Unknown Source)
at java.lang.Class.getConstructor(Unknown Source)

Answer 1

java.lang.Integer has not constructor that takes a Number as its argument.

Reading the stacktrace that you got would have told you that (possibly in a slightly cryptic way, but the info is there). You should at least post the stack trace when you’ve got a question about it.