NawaMan's Blog

Examples of Signature

// @Java: { main } 

or

// @Java: 

are both main for a script in Java.

Imports

Import section contains a set of import statements. The section is identified by the keyword "import" immediately follows by at least one whitespace. Comments and whitespaces are allowed between import statements just like in Java. In fact, the whole chunk of the section will be used as is in the translated code. Therefore, it is subject to the semantic checking by Java compiler.

Example of Imports

The following is a valid Imports section.

import java.io.*;
import static java.lang.Math.PI;

import java.util.Vector;

Elements

"Everything in Java is object," I bet that you have heard this quote. Although it is not perfectly correct by it is very close. Almost everything in Java is object. Thus, a SimpleScript executable is also an object. As an object, an executable can have elements just like other objects. The elements can be fields or methods. They can also be static. They can have public, private, protected or package accessibility (although this does not seems to matter as they make no different). They can also be final (again, no different).

Since there is no class structure in script files, SimpleScript identifies elements section by checking the position and keywords. After SS identify the imports, it looks for a valid Java statements which either ends with ';' or a body '{'...'}'. If SS finds a statement, it checks if the beginning word is one of the following: static, public, private or protected as these keywords are only used for elements. Then it looks for more elements until no more element is found.

Script writers can create functions (methods) to be used with in the script either as sub-routine or as a mean to document a part of the code. Since these functions will not likely to be called from any other piece of code (except through reflection), it does not make any difference what its accessibility and modifier are. However, script writer may choose to make a function non static if it is needed to access to pre-defined elements which are non-static.

By default, an executable is created (or loaded) once and may be executed more than one time. Because of this nature, it makes almost no difference if a field should be static or non-static with only one exception that is if the field is to be accessed by static functions, it cannot be non-static. Generally, fields have two uses in script: 1) to hold constants and 2) to hold cached values.

Examples of Elements

// Use private as an indicator that this is a field and not a regular variable as part of the code.
private int non_static_field = 0;
// It does not matter private or public, they just indications for elements.
public int non_static_field2 = 5;
// This is for a constant
static final int static_field = 10;
// This is for a complex constant
static final Vector ints = new Vector();
static {
    ints.add(5);
    ints.add(10);
}
// function as documentation
private String[] getFileList(final String $PathName) {
    // Get file list and return
    return ...;
}
// function as subroutine (in this case for, for recursive)
private int factorial(int I) {
    // Find factorial and return
    return ...;
}
// An annotation for functions must be put after the indicator.
private @annotate int getInt() {
}
// You can even create a class
static class Task1 implements Runnable {
    // implements Runnable
}

Annotations

This section allows script writers to declare annotation for the code. Annotation such as '@SuppressWarnings('...')' is needed to hide certain compilation warnings. Other annotation such as '@Test' may also be used.

Examples of Annotations

// @Java:

import java.util.*;

// Tell compiler to produce no warning about unchecked generic-type
@SuppressWarnings("unchecked")

// A warning should be generated here but it is suppressed
final Class C = this.getClass();
System.out.println(C);

Code

This section is where the actions are. SimpleScript recognizes this section simply by checking if it is not an import, an element, an annotation nor a compiled code. The text in this section will be put into a body of a method in its entirety. In other words, writing this section is like writing a body of a method -- a non-static method to be precise.

Since this part of code is copied to the final code without any modification and it is compiled directly by the Java compiler, you can be sure that the code will be 100% Java compatible. Everything that can be done in a Java method can be done here. This includes things like calling other classes' methods to creating inner classes. So, bring it on.

Compiled Code

This section of the code is not to be written but rather generated by SimpleScript. It contains a text representation of the compiled code. Information provided here is used when the code the is executed. Starting by checking of the compiled code is synchronized with the code. This is done by checking the hash and the length of both the code and the compiled code. If hash or length of either ones changed, the code will be recompiled.

Compiled code section will always three empty lines away from the last line of the code and it always with in a long comment block. SS starts parsing by looks at the last two lines after the last line finding "##:HASHES" and "##:COUNT". Using count, SS can locate the beginning of the compile code. It is, then, looks for "##:COMPILED" that the beginning. At this point, SS can separate the code from the compiled code and checking hashes can commence. If the checking is success, the compiled code will be obtained by converting from its Base64 and loaded as a serializable object. Casted and wrapped, it is then a ready to be used as an executable object.

Of course, you don't need to care about all this if you are just using SS for scripting (not modifying nor writing a script engine for it). The importance here is that when a script is first run, its code is compiled and the resulted byte code will be recorded at the end of the script. If the byte code can't be saved or the script file content has changed, the code will be recompiled again in the next run.

An implication for this is that, there is a performance overload for loading a script and a little bit for invoking it (parameter handling) but there is absolutely no performance different between code written with script or a regular Java code when the code is actually running.

Put all of these together

Let see the code that has every section. Just to remind that the last section is generated by SimpleScript and script writers does not need to write it.

#!/usr/bin/ss --run
# This line will be ignored as it starts with "#"
  This line will be ignored as it ends with "##"           ##
  This line will be also ignored as it also ends with "##" ##
# The line is the signature
// @Java:

// Imports
import java.io.*;
import java.util.*;

// Elements
static  int I = 0;
private int factorial(int $I) {
	return ($I <= 1) ? 1 : $I * factorial($I - 1);
}

// Annotations
@SuppressWarnings("unchecked");

// The program start here
System.out.println("Hello World!!!");
System.out.println();

System.out.println("Main Args = " + Arrays.toString($Args));	// Access Args
System.out.println();

System.out.println("static int I = " + I);
System.out.println();

System.out.println("Working Dir: " + (new File(".")).getAbsolutePath());
System.out.println();

final Class C = this.getClass();
System.out.println("This class: " + C.getCanonicalName());
System.out.println();

System.out.println("Factorial using local method");
for(int i = 0; i < 10; i++)
	System.out.println(i+"! = " + factorial(i));
System.out.println();

System.out.println("DONE!!!");

/*******************************************************************************
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}
##:HASHES:0x   15BFA-0x   6EC94;
##:COUNTS:0x     443-0x    15B8;
*******************************************************************************/

Enough for now

I hope this post should provide some interesting insight into the structure of scripts as well as how SimpleScript processes it. Next time, I will talk about what happen when things go wrong.

NawaMan
Bye bye.