In bytecode you have a nop instruction, but there’s no nop statement in the Java language.
You can add an extra ; on a line by itself and the code will still compile, but that’s not much more meaningful than adding an empty line.
Another “does nothing” statement could be:
assert true;
which has no side-effects what so ever, and can be turned off when executing the program.
As it turns out, assert true does not seem to generate any bytecode instructions, which causes break-points on assert true to be skipped all together. Eclipse is however able to break on a statement such as
assert Boolean.TRUE;
which is quite similar.