Dynamic Class Loading allows the loading of java code that is not known about before a program starts. Many classes rely on other classes and resources such as icons which make loading a single class unfeasible. For this reason theClassLoader (java.lang.ClassLoader) is used to manage all the inner dependencies of a collection of classes. The Java model loads classes as needed and doesn't need to know the name of all classes in a collection before any one of its classes can be loaded and run.

An easy way to dynamically load aClass is via thejava.net.URLClassLoader class. This class can be used to load aClass or a collection of classes that are accessible via a URL. This is very similar to the-classpath parameter in thejava executable. To create aURLClassLoader, use the factory method (as using the constructor requires a security privilege):

Code section 10.4: Class loader. URLClassLoaderclassLoader=URLClassLoader.newInstance(newURL[]{"http://example.com/javaClasses.jar"});

Unlike other dynamic class loading techniques, this can be used even without security permission provided the classes come from the same Web domain as the caller.Once aClassLoader instance is obtained, a class can be loaded via theloadClass method. For example, to load the classcom.example.MyClass, one would:

Code section 10.5: Class loading. Class<?>clazz=classLoader.load("com.example.MyClass");

Executing code from aClass instance is explained in theDynamic Invocation chapter.

To do: Add some exercises like the ones inVariables

• Book:Java Programming

• Pages using the JsonConfig extension
• Wikibooks pages with to-do lists