Here's a familiar feeling. You want to test one small thing in Java — maybe how String.substring() behaves, or whether a regex pattern matches. So you create a file, write a class, add a main method, type System.out.println , compile, run. All that ceremony for a one-line answer. JShell does away with the ceremony. It's a read-eval-print loop (REPL) that ships with the JDK since Java 9. You type Java code, press Enter, and see the result immediately. No class, no main method, no compil...