Supported: classes with main (or just bare statements — no class needed), static and instance methods, constructors, recursion, overloading by argument count, int/long/double/boolean/char/String/var, 1-D and 2-D arrays, all operators with real Java semantics (32-bit int wrapping, integer division, long is 64-bit), if/else, for, enhanced for, while, do-while, switch, try/catch/finally with real exceptions, String/StringBuilder/Math/Integer/Character/Arrays methods, ArrayList, HashMap, HashSet, Random, Scanner (reads the stdin box), System.out.println/print/printf and String.format.

Not supported: inheritance, interfaces, generics type-checking (parsed but ignored), lambdas and streams, threads, file or network I/O, imports beyond the built-ins (parsed and ignored). == on strings compares values here, unlike real Java. Execution stops after 20M steps, 256 KB of output, or 10 seconds.