Invoking Methods of Class Instances

JVM Tutorials - Herong's Tutorial Examples

∟Invoking Methods of Class Instances

This section provides a tutorial example on how to reflect class methods as Method instances and invoke them directly.

Once a class is loaded as a Class instance, you can reflect its methods as Method instances and invoke them directly like this:

   ClassLoader l = ClassLoader.getSystemClassLoader();
   Class c<?> = l.loadClass(className);
   // Object o = c.newInstance(); // deprecated
   Object o = c.getDeclaredConstructor().newInstance();
   Method m = c.getMethod(methodName, parameterTypes);
   m.invoke(o, args);

Here is tutorial example program showing you how to invoke a method reflected as a Method instance:

/* ClassMethodReflection.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.lang.reflect.*;
class ClassMethodReflection {
   static java.io.PrintStream out = System.out;
   public static void main(String[] a) {
      try {
         // Loading the class and creating an object
         ClassLoader l = ClassLoader.getSystemClassLoader();
         Class<?> c = l.loadClass("java.util.Random");
         Object o = c.getDeclaredConstructor().newInstance();
         Method m = c.getMethod("nextInt", int.class);

         // Invoking the method: o.nextInt(100)
         Object r = m.invoke(o, 100);
         out.println("Random number between 0 and 99: "+r);
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}

When executed, I got this result:

herong> java ClassMethodReflection
Random number between 0 and 99: 66

herong> java ClassMethodReflection
Random number between 0 and 99: 23

herong> java ClassMethodReflection
Random number between 0 and 99: 47