While JRuby, BeanShell, Julian Fleischer’s REPL are there Albert Latacz’s REPL seems to be the latest and active.
Tried it with a class definition (made the class look like this by design to try as many language elements as possible), works fine.
$ java -jar javarepl.jar
Welcome to JavaREPL version 56 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_17)
Type in expression to evaluate.
Type :help for more options.
java> public class Test {
| public static void execute(String [] s) {
| System.out.println(54353 + s[0]);
| }}
java> Test.execute(new String [] {"234343"});
54353234343
java> System.exit(0);
References: [StackOverFlow]