Dynamic Class Loading
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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 the
java.lang.ClassLoader) is used to manage all the inner dependencies of a collection of classes. The Java model loads classes as needed and need not know the name of all classes in a collection before any one of its classes can be loaded and run.
Simple Dynamic Class Loading
An easy way to dynamically load a
Class is via the
java.net.URLClassLoader class. This class can be used to load a
Class or a collection of classes that are accessible via a URL. This is very similar to the
-classpath parameter in the
java executable. To create a
URLClassLoader, use the factory method (as using the constructor requires a security privilege):
|Code section 10.4: Class loader.
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 a
ClassLoader instance is obtained, a class can be loaded via the
loadClass method. For example, to load the class
com.example.MyClass, one would:
|Code section 10.5: Class loading.
Executing code from a
Class instance is explained in the Dynamic Invocation chapter.