In this tutorial, we will learn how to perform the following in Java 9:

• How to start JShell
• Basic commands
• Unassigned and assigned variables
• Classes
• Methods
• If and For loop
• Imports
• JShell autocompletion

Start Console

The JShell can be started by a command:

jshell

The end result should look like the following:

test@test:~$ jshell
|  Welcome to JShell -- Version 9-internal
|  For an introduction type: /help intro

Basic Commands in JShell

Here, you can find several useful commands while working with JShell:

• /exit — if you want to quit the current session. Another option for Ubuntu Shell is by pressing: CTRL+Z
• /vars — list of all JShell variables — both unassigned and assigned (check section variables). The result should look like the following:

-> /vars
|    int x = 10
|    String $2 = "Java 9"
|    Test ts = Test@42e26948
|    int $11 = 10
|    int $12 = 10

• /methods — list of JShell methods

-> /methods
|    printf (String,Object...)void
|    printX ()void

• /imports — all JShell imports

-> /imports 
|    import java.util.*
|    import java.io.*
|    import java.math.*
|    import java.net.*
|    import java.util.concurrent.*
|    import java.util.prefs.*
|    import java.util.regex.*
|    import java.util.Arrays

• /classes — all JShell classes

-> /classes
|    class Test

• /list — JShell snippets if any

-> /list 

   1 : int x = 10;
   2 : "Java 9"
   3 : System.out.println($2);
   4 : class Test {
       }
   5 : Test ts = new Test();
   6 : System.out.println(ts);
   7 : void printX(){
       System.out.println("X");
       }
   8 : printX()
   9 : import java.util.Arrays;
  10 : if(x > 0){
       System.out.println(x);
       }
  11 : 10

Assigned and Unassigned/Temporary Variables

This is how the assigned variable are declared (notice that you don't need to put any semicolons):

• Assigned variable

-> int x = 10
|  Added variable x of type int with initial value 10

• Unassigned variable

-> "Java 9"
|  Expression value is: "Java 9"
|    assigned to temporary variable $2 of type String

In order to access a temporary variable, you need to write:  $2 

-> System.out.println($2);
Java 9

Define Classes in JShell

If you want to add a new empty class test, then, you need to write only:  class Test {} 

-> class Test {
>> }
|  Added class Test

Creating a new instance in JShell is the same as in Java and the access to the class methods and variables:

-> Test ts = new Test()
|  Added variable ts of type Test with initial value Test@42e26948

-> System.out.println(ts);
REPL.$REPL12$Test@42e26948

Method Declaration in JShell

Declaring the new method can be done the same way as a class. You can start with the type and the method line-by-line, using semicolons and enter:

-> void printX(){
>> System.out.println("X");
>> }
|  Added method printX()

You need to use semicolons with methods. The following is an executed method in JShell.

-> printX()
X

JShell Autocompletion

If you use TAB, you will find all possible commands starting with the current text:

-> print
printX()   printf(    

JShell Imports

You can add new imports to JShell by:

import java.util.Arrays;

To view all imports, use the /imports  command:

-> /imports
|    import java.util.*
|    import java.io.*
|    import java.math.*
|    import java.net.*
|    import java.util.concurrent.*
|    import java.util.prefs.*
|    import java.util.regex.*
|    import java.util.Arrays

JShell For and If

If, in JShell, there is an assigned variable:

-> if(x > 0){
>> System.out.println(x);
>> }
10

Here is the for  loop:

-> for(int i=0;i<5;i++){
>>  System.out.println(i);
>> }
0
1
2
3
4