Hello, World!! JavaShell Introduction Part 2

##This guide is written on Release 0.1.x

#This is a Hello, World guide on JavaShell. Part 2.

If you haven't done it yet, please follow Part 1 first.

You will be creating a Hello World program in this part of the tutorial.

Load the javashell if you haven't already.

java JavaShell

##Goal We will be writing the code that mimics the behaviour of the following java code.

System.out.println("Hello,_World!!!");

##1. Construct a Hello,_World String

To construct a string, we will use java.lang.String(String s) constructor.

>>> load java.lang.String Hello,_World!!!

Note: as of current release, JavaShell cannot distinguish spaces with escapes, please put a underline _ between Hello and World.

We can confirm that our construction is successful using toString method.

java.lang.String >>> ls
java.lang.String >>> toString

##2. Store the string into the bindings table

We will name the string object str

java.lang.String >>> bind str

##3. Gets the System.out

Getting System.out directly will be somewhat complicated. We will use a help method, sysout in our standard library shown below.

File : JavaShellStandardLibrary.java

public class JavaShellStandardLibrary {

	public PrintStream sysout(){
		return System.out;
	}
	
	//other methods
}

We will get the System.out by instantiating our standard library and call the sysout() method.

java.lang.String >>> load JavaShellStandardLibrary
JavaShellStandardLibrary >>> sysout

The sysout method returns a print stream, which is captured in rtObj in our bindings table. We can get it by unbind it from the bindings.

JavaShellStandardLibrary >>> unbind rtObj
java.io.PrintStream >>> ls

##4. Print Hello,_World!!!

We can do this by calling the println(String) method on the System.out stream.

java.io.PrintStream >>> println str

We can see that the Hello,_World is actually printed, among all the messy informations.

##5. Clean it up

Hit Ctrl-D to exit the shell. Create a file under the current directory name MyFirstJavaShellScript.jss, and type in the following command.

File : MyFirstJavaShellScript.jss

load java.lang.String Hello,_World!!
bind str
load JavaShellStandardLibrary
sysout
unbind rtObj
println str

Execute the file with following command.

$ java JavaShell MyFirstJavaShellScript.jss

Hopefully you will see the beautiful Hello,_World!!! output.