Java Shell & REPL | no more public static void main
What is REPL?
R(ead) E(val) P(rint) L(oop), is an interactive programming environment that allows you to enter code snippets or expressions and immediately see the results of their evaluation.
This makes it easy to experiment and test out ideas by scripts.
REPLs are commonly used for scripting languages like Python, and JavaScript, but they can be used for any language that supports interactive evaluation of code such as Java, Kotlin, Clojure.
REPL in Java
With the release of Java 9, the Java development community was introduced to JShell, an official REPL tool that provides a streamlined and interactive way to write, test, and experiment with code snippets.
How to run JShell?
To start JShell, enter the jshell command on the command line.
Useful JShell commands
Enter the /help command on the command line to see details.
/list => list the source you have typed
jshell> /list
1 : import java.lang.String;
2 : "Hello world!".toUpperCase().split(" ");
3 : var a=5;
4 : String name = "gurkan";
/vars => list the declared variables and their values
jshell> /vars
| String[] $3 = String[2] { "HELLO", "WORLD!" }
| int a = 5
| String name = "gurkan"
/methods => list the declared methods and their signatures
jshell> int sum(int x,int y){ return x+y;}
| created method sum(int,int)
jshell> sum(10,20);
$9 ==> 30
jshell> /methods
| int sum(int,int)
/imports => list the imported items
jshell> /imports
| import java.io.*
| import java.math.*
| import java.lang.String
| import java.util.*
/exit => to exit the jshell tool, ctrl+c won’t work!
jshell> /exit
| Goodbye
Examples
Date-Time functions example
Class example
Streams example
Resources
https://www.digitalocean.com/community/tutorials/java-repl-jshell
https://www.tutorialspoint.com/how-to-implement-java-time-localdate-using-jshell-in-java-9
https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop
https://docs.oracle.com/javase/10/jshell/introduction-jshell.htm
https://www.infoworld.com/article/2971152/what-repl-means-for-java.html