I am successfully loading a class from an external MyClass.class
file at runtime, and am able to call it's methods assuming I know the name of them, which I do.
The problem I'm having is I cannot figure out how to pass a parameter to the constructor of the class I am loading.
How can I modify this to pass a parameter to MyClass
's constructor? Also, how can I access MyClass
's public variable: infoToAccess
?
Here are the files I'm working with. (Keep in mind, ClassLoaderExample.pde was written for Processing, but other than sketchPath("")
and the lack of a main
function, it is identical.
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.MalformedURLException;
import java.lang.ClassLoader;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
/////// FILE STRUCTURE /////
// ClassLoaderExample //
// --this file //
// --tmp //
// ----MyClass.class //
////////////////////////////
// TODO
// Send parameter to MyClass constructor (by reference)
// Get public int number from MyClass
void setup()
{
String className = "MyClass";
Object instance;
Method updateMethod;
// sketchPath("") returns the directory this file is in
File file = new File(sketchPath(""));
try
{
URL url = file.toURL();
URL[] urls = new URL[]{url};
ClassLoader classLoader = new URLClassLoader(urls);
Class<?> loadedClass = classLoader.loadClass("tmp."+className);
try
{
instance = loadedClass.newInstance();
updateMethod = loadedClass.getDeclaredMethod("update");
// Calls MyClass's update() method
try
{
updateMethod.invoke(instance);
}
catch (InvocationTargetException e) {System.out.println(e);}
catch (IllegalAccessException e) {System.out.println(e);}
}
catch (InstantiationException e) {System.out.println(e);}
catch (IllegalAccessException e) {System.out.println(e);}
catch (NoSuchMethodException e) {System.out.println(e);}
}
catch (MalformedURLException e) {System.out.println(e);}
catch (ClassNotFoundException e) {System.out.println(e);}
}
package tmp;
public class MyClass
{
public int infoToAccess = 1337;
public MyClass(int i)
{
System.out.println("MyClass constructor was called with numebr: " + i);
}
public void update()
{
System.out.println("Update was called.");
}
}
Thanks for any help with this!
you can use the class you loaded to get hold of the constructor you need an use that to create a new instance.
import java.lang.reflect.Constructor;
...
Class<?> loadedClass = classLoader.loadClass("tmp."+className);
try {
Constructor<?> ctor=loadedClass.getConstructor(int.class);
ctor.newInstance(42);
...
}
...