Java online compiler

What this runtime cannot do

It is a real compiler but not a full JVM, and the honest version of that is worth knowing before you hit it:

• No input. There is no Scanner and no standard input — put your values in the code.
• Runtime errors are not catchable. Dividing by zero, running off the end of an array or using a null reference stops the program outright instead of throwing something a catch can hold. Exceptions you throw yourself work normally.
• e.getMessage() is unavailable — use e.toString() instead.
• Threads do nothing. Code that starts one compiles and runs, and simply never executes.
• No System.exit(), and %f and %n in format strings do not work.
• An escaped %% works only when nothing is formatted after it: "%d%% done" is fine, "10%% = %d" fails, because the %% throws the argument numbering out of step. Putting the percent sign in ordinary text outside the pattern always works.
• Math.round disagrees with a real JVM on a negative half — Math.round(-2.5) is -3 here and -2 on the JDK. Worth knowing because it is a wrong answer rather than an error.

Everything a beginner normally meets does work: classes, methods, arrays, loops, conditionals, collections, generics, records, streams, String handling and Math.