Java interpreter code at runtime

Question

We have discussed how java is first compiled into Java bytecode and then interpreted by the JVM. Build into the program we are using (Dr Java), there is a panel called Interactions where you can type code in real time and have it be interpreted and ran (I believe that is how it works). I was wondering if it was possible to have a compiled program in java be ran, and then allow a user to input java code to be interpreted to modify the things that happen. I can't really think of any practical uses of this, but here is an example to clarify:

User runs a program and an integer in initialized with the value of 2 and the name of changeNumber. A pop-up comes up allowing the user to input some java code. They can input something like - "changeNumber = changeNumber + 2;" and have the code execute in real time where if you ended up printing out changeNumber, you would get 4.

The simplest answer that comes into my mind is: take a look at Groovy: groovy.codehaus.org. It's a Java language extension which inherently allows what you are looking for. — Jack
– Jack, Commented Sep 18, 2013 at 17:38
Sure, parse the input and add a touch of reflection. I wouldn't advise you to look into this just yet though. — Jeroen Vannevel
– Jeroen Vannevel, Commented Sep 18, 2013 at 17:40
possible duplicate of Runtime code generation and compilation — om-nom-nom
– om-nom-nom, Commented Sep 18, 2013 at 17:49

Uku Loskit · Accepted Answer · 2013-09-18 17:42:53Z

3

This is possible using the Reflection API.

As a side note, I do not understand the downvotes. This is a good and well-written question for a beginner.

answered Sep 18, 2013 at 17:42

Uku Loskit

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om-nom-nom Over a year ago

Personally, I have downvoted this question because it lacks any research effort -- there are tons of resources in the internet on the topic, e.g. first result in google with query java runtime code leads to this stackoverflow question

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