How to declare an object created by a class loaded by classloader

Question

I have to use a classloader to load a class from a custom jar file, and the following works:

Class<?> JasperPrint = urlClassLoader.loadClass("net.sf.jasperreports.engine.JasperPrint");

How to I declare an object I create with the constructor? Below, Eclipse complains that JasperPrint is not an object:

JasperPrint jp = JasperPrint.getConstructor().newInstance();

Also just to declare an object without instantiating, since the following also does not work:

JasperPrint jp;

Answer 1

Your JasperPrint is not a class. It is a variable holding the loaded Class definition net.sf.jasperreports.engine.JasperPrint. On a Class instance you can call newInstance() to create a new instance using the no-arg constructor:

Class<?> jasperPrintClazz = urlClassLoader.loadClass("net.sf.jasperreports.engine.JasperPrint");
Object jasperPrint = jasperPrintClazz.newInstance();

Variable jasperPrint is an instance (object) of type JasperPrint.

Answer 2

If you are loading a class dynamically you do not know it's static type (at compilation type). You can either cast it to a JasperPrint 's interface if you have it on your classpath when compiling your code. Otherwise you will need to use reflection to call the newly created object's methods.