How to run Java code using Java code?

Basically, I want to do two things:

1. I want to know if there is any way that I can run Java code using Java code.
2. If it is possible, how would I show the output on my screen? (be it regular output or error or exception)

I know this is possible because one of my seniors开发者_如何学JAVA had done it, but I don't know how he did it. Maybe he used one of Java's built-in classes.

Note: user will write the code in some text file and then I will store that file content in some variable and then maybe run that code.

Yes, it is possible.

Step 1: Compile the Code
Use ProcessBuilder or Runtime to construct a Process in which the Java compiler compiles their code. (Note that this requires that a Java compiler be available on the system at runtime).

Step 2: Invoke their Code
There are two ways to invoke their code. You can again use a ProcessBuilder or Runtime object to construct a process in which you execute their Java code. You can use the Process's getInputStream and getOutputStream functions to read from and write to the other process. An alternative is that you can use Class and the various reflection APIs to load their code and execute it directly within Java.

You would have to some how invoke a compiler (such as Suns javac), parse its output in case of errors and load the resulting classes dynamically.

There is no API-classes in the Java runtime library that will parse, compile and run Java source code.

If you want an interpreter (so, no compiling required) for Java, take a look at BeanShell.
I like this one very much!

You can use a scripting language running on top of the JVM. Groovy is a very good idea and it has very similar syntax compared to Java.