Extending or adding new classes at runtime in Java

Question

Hello all, Is there a way to add (or extend existing) classes at runtime in java. I'm stuck on a problem, in which I have to extend an existing class at runtime and add this to the classpath, so that this new class get picked up.

thanks,

Answer 1

You might want to look at BCEL. Without any more information about what you need to do, it's tricky to give a more specific answer.

Answer 2

You should definitely write why you need this feature. If you attempt to add or replace logic at runtime you might want to have a look at the scripting API and some actual implementations.

Answer 3

There are a number of ways you could do this.

• Compile source code at runtime using the javax.tools package and then load them using a ClassLoader.
• If you are writing to interfaces, you can decorate classes with a Proxy.
• Take the more complicated route of bytecode manipulation/generation using a technology like BCEL or ASM (the latter has more up-to-date support for language features, like annotations) and then load the class with a ClassLoader.

I imagine there are other options.