Java Reflections Tutorial

This tutorial gives an insight on how Java Reflection can be used to load Java classes dynamically at the run time. Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine.

package com.kushal.utilities;

/**
 * @author Kushal Paudyal
 * 08/05/2008
 * 
 * Simple demonstration of Java Reflection mechanism to
 * instantiate a class, get it's method and call that
 * method with proper parameter passing.
 */
import java.lang.reflect.*;

public class JavaReflectionsDemo {

	public static void main(String args[]) {
		try {
			/*
			 * Step 1 Define a class loader
			 */
			ClassLoader myClassLoader = ClassLoader.getSystemClassLoader();
			/*
			 * Step 2: Define a class to be loaded.
			 */
			String classNameToBeLoaded = "com.kushal.utilities.DemoClassToBeLoaded";

			/*
			 * Step 3: Load the class
			 */
			Class myClass = myClassLoader.loadClass(classNameToBeLoaded);

			/*
			 *Step 4: create a new instance of that class
			 */
			Object whatInstance = myClass.newInstance();

			String methodParameter = "ABC";
			/*
			 * Step 5: get the method, with proper parameter signature.
			 * The second parameter is the parameter type.
			 * There can be multiple parameters for the method we are trying to call, 
			 * hence the use of array.
			 */

			Method myMethod = myClass.getMethod("myMethod123",
					new Class[] { String.class });

			/*
			 *Step 6:
			 *Calling the real method. Passing methodParameter as
			 *parameter. You can pass multiple paramters based on 
			 *the signature of the method you are calling. Hence
			 *there is an array. 
			 */
			String returnValue = (String) myMethod.invoke(whatInstance,
					new Object[] { methodParameter });

			System.out.println("The value returned from the method is:"
					+ returnValue);

			/*
			 * Catching Probable Exceptions
			 * You can simply catch the Generic 'Exception' to reduce your coding.		 
			 */
		} catch (ClassNotFoundException e1) {
			System.out.println("EXCEPTION:CLASS NOT FOUND");
		} catch (IllegalAccessException e2) {
			System.out.println("EXCEPTION:ILLEGAL ACCESS");
		} catch (InstantiationException e3) {
			System.out.println("EXCEPTION:INSTANTIATION EXCEPTION");
		} catch (NoSuchMethodException e4) {
			System.out.println("EXCEPTION:NO SUCH METHOD");
		} catch (InvocationTargetException e5) {
			System.out.println("EXCEPTION: INVOCATION TARGET");

		}
	}

}
/**
 * @author Kushal Paudyal
 * 08/05/2008
 * www.sanjaal.com/java
 */

/*
 * This is the demo class that we will use to load and invoke method
 * using Java Reflection.
 */
class DemoClassToBeLoaded {
	public static String myMethod123(String someParam) {
		System.out.println("You Are Calling myMethod()");
		System.out.println("You Passed " + someParam + " as Parameter");

		/*
		 * Just returning the current class name
		 * This is just an example method. 
		 */
		return DemoClassToBeLoaded.class.getName();
	}

}