Free java class example software for linux

RJCE allows all methods or variables of user defined classes to be altered at runtime. These alterations are then applied to a single instance, a collection of instances (i.e. list, set or map), or an entire class.

This helps you to test your application in an interactive way; altering running programs helping a trial and error approach to programming; testing code and saving it when it’s correct. Long running algorithms, such as simulations, can also easily be refined without the need for restarts or lose of data.

RJCE can be used to write a program from within itself ensuring high coupling between testing and development, with no delay before the outcome of any alterations.

RJCE allows scripts to run from within your application, allowing users to configure or extend an application dynamically, bypassing normal language access rules controlled by public, private and protected. This can be done by easily instatiating an instance of CodeEditorFrame from the rom.gui package.

RJCE permits faster development of applications by allowing easy migration from scripts to Java programs.

Java::Import::Examples is an example of how to use Java::Import to call into Java classes.

Making RMI calls from Perl

One nice thing about Java is the extremely straight forward manner in which it allows you to make calls to remote objects residing on distant servers. Many people use this ability as a point of integration between their system and a posible third party or legacy system. Unfortunatly, for the most part the ability to make calls to these remote objects is something that only other Java applications can do without making a big fuss about it. However, we can now do this from Perl.

Assume that I have a RMI server from which I can get data from in the form of simple Java Beans. One method of doing this is to use the GCJ::Cni library and natively compile and wrap a set of Java Classes which can then be used from my Perl script. However, there is an easier way.

Lets begin by descriping the Java interfaces that well be working with. We first have the Remote Interface that we will be interacting with:

import java.rmi.*;
public interface RemoteInterface extends Remote {
public SomeBean getMessage(String seedMessage) throws RemoteException;
}
And we also have the bean we will be asking for:
import java.io.*;
public class SomeBean implements Serializable {
private String value;
public SomeBean() {}
public void setValue ( String _value ) { ... }
public String getValue ( ) { ... }
}
As far as any Perl client program is concerned this is all we need to know about.
Now all there is left to do is write a client:
use Java::Import qw(
java.rmi.Naming
);

my $remote_interface = java::rmi::Naming->lookup(jstring("//localhost/Home"));
my $bean = $remote_interface->getMessage(jstring("Hi there"));
print $bean->getValue(), "n";

Thats all there is. Notice that all we had to tell Java::Import about was java.rmi.Naming, this is because it was the only class we used by name in our Perl code, every other Java class (the objects held by $bean and $remote_interface) was returned by some other method call originating from java.rmi.Naming.

In order to run this example we have to make sure everything is in its place. We start by compiling the client code. Assuming that we have been given a Stub class file (RemoteObject_Stub.class) we can do the following:

gcj -C SomeBean.java RemoteInterface.java
fastjar -cvf client.jar SomeBean.class RemoteInterface.class RemoteObject_Stub.class

Making sure our server is reachable we can then run the client code:

CLASSPATH=client.jar perl client.pl

Thats it, you should then see the message returned by your server.

Asm2class is a java assembly to class file compiler.

Asm2class is release under the terms of the GPL License. The current version of asm2class (0.1.2) is a beta version and allow generating class file from java assembly file that contains class definition, field definition, method definition and constructor definition.

This release support also abstract class, abstract method and native method definition.

Asm2class know more thatn 90% of the java assembly language. Asm2class can do dead code detection, uninitialized register detection.

Class::HPLOO is an easier way to declare classes on Perl, based in the popular class {...} style and ePod.

USAGE

use Class::HPLOO ;

class Foo extends Bar , Baz {

use LWP::Simple qw(get) ; ## import the method get() to this package.

attr ( array foo_list , int age , string name , foo ) ## define attributes.

vars ($GLOBAL_VAR) ; ## same as: use vars qw($GLOBAL_VAR);

my ($local_var) ;

## constructor/initializer:
sub Foo {
$this->{attr} = $_[0] ;
}

## methods with input variables declared:
sub get_pages ($base , @pages , %options) {
my @htmls ;

if ( $options{proxy} ) { ... }

foreach my $pages_i ( @pages ) {
my $url = "$base/$pages_i" ;
my $html = get($url) ;
push(@htmls , $html) ;
$this->cache($url , $html) ;
}

return @htmls ;
}

## methos like a normal Perl sub:
sub cache {
my ( $url , $html ) = @_ ;
$this->{CACHE}{$url} = $html ;
}

sub attributes_example {
$this->set_foo_list(qw(a b c d e f)) ;
my @l = $this->get_foo_list ;

$this->set_age(30) ;
$this->set_name("Joe") ;
$this->set_foo( time() ) ;
print "NAME: ". $this->get_name ."n" ;
print "AGE: ". $this->get_age ."n" ;
print "FOO: ". $this->get_foo ."n" ;
}

}

## Example of use of the class:

package main ;

my $foo = new Foo(123) ;
$foo->get_pages(http://www.perlmonks.com/, [/index.pl,/foo] , {proxy => localhost:8080}) ;

GCJ::Cni::Examples is a Perl module with examples of how to use GCJs CNI interface to write Perl Modules in Java.

EXAMPLES

Writing Treaded modules in Java

One benefit of using GCJ is that it takes advantage of POSIX threading. This is nice since Perls threading model is, shall we say, less than ideal. Now, you could theoretically write a module in C or C++ and and use the standard POSIX library to do your threaded work for you, however, why not take advantage of the nice Threading interface that Java provides to you by default. This may also come in handy if you have a massively threaded Java library that youd like to call from Perl.

For this example assume that I want to do matrix multiplication, albeit in a very crazy manner. Therefore, I will write a Java class, Matrix, and a method, multiply, which will take another matrix to perform the operation between. Heres the crazy part, for each cell in the resulting matrix I will spawn a new thread, as an internal class, and give it a row and a column from which they will derive the result. I know this is a little wierd but the point is that Ill be spawning a lot of new threads. To multiply two 10x10 matrices we will have to spawn 100 threads (one thread per cell in the resulting 10x10 matrix). Imagine doing this in Perl, then imagine doing it in Java; natively compiled Java. Much faster and a lot less headaches.

The Java Interface/pseudocode is as follows:

public class Matrix {
public Matrix ( int numRows, int numCols ) {
...Constructor stuff...
}

public void set ( int row, int col, int val ) {
...set an element...
}

public int get ( int row, int col ) {
...get an element...
}

public Matrix multiply ( Matrix times ) {
...set it up...
for ( int i = 0; i < rows; i++ ) {
for ( int j = 0; j < times.getCols(); j++ ) {
//GO NUTS!!!!
ArrayMultiplier multiplier = new ArrayMultiplier(this, times, result, i, j);
multiplier.start();
...etc...
}
}
...wait for the threads to exit and return the new matrix...
}

public int getRows ( ) {
...get number of rows...
}

public int getCols ( ) {
...get number of columns...
}

public void print ( ) {
...print the matrix to stdout...
}

private class ArrayMultiplier extends Thread {
public ArrayMultiplier ( Matrix a, Matrix b, Matrix result, int row, int col ) {
...Construct this bad boy...
}

public void run ( ) {
int sum = 0;
for ( int i = 0; i < a.getCols(); i++ ) {
sum += (a.get(row, i) * b.get(i, col));
}
result.set(row, col, sum);
}

}
}
Now, we want to call this class from Perl. My perferred manner is through SWIG so thats what were going to use. However, you do not need to use SWIG, you can use whatever method you prefer when wrapping C++ classes. We begin by creating a C++ header file from our above class. This is done by using GCJs gcjh utility. First we need to class compile Matrix.java

gcj -C Matrix.java

Then we go ahead and create the header file:

gcjh Matrix

Easy enough. We can then extract the interface we want to have available in Perl from the generated header file and from it create a i file to be used as input to SWIG. I usually start by copying my header file to the same named file but with an i extension instead. I then remove all of the grimy C++ gruff, private methods and variables, slap a module directive on it and call it done. It wont always be this easy though. When youre done an interface file for the above class should look something like this:

%module Matrix;

typedef int jint;

class Matrix
{
public:
Matrix (jint, jint);
virtual void set (jint, jint, jint);
virtual jint get (jint, jint);
virtual ::Matrix *multiply (::Matrix *);
virtual jint getRows ();
virtual jint getCols ();
virtual void print ();
};
We then put SWIG to work and generate our C++ wrapper for Perl:

swig -perl -c++ Matrix.i

After the above command we now will see two new files in our current directory, Matrix.pm and Matrix_wrap.cxx; these correspond the module directive we gave in Matrix.i.

At this point all we have left to do is compile, and use.

gcj -c Matrix.java
gcc -c -I -include Matrix.h Matrix_wrap.cxx
gcc -shared -lgcj -lstdc++ Matrix.o Matrix_wrap.o -oMatrix.so

A simple Perl file using this module might look something like:

sub populate_matrix {
my $matrix = shift;
for ( my $i = 0; $i < $matrix->getRows(); $i++ ) {
for ( my $j = 0; $j < $matrix->getCols(); $j++ ) {
$matrix->set($i, $j, $i * $j);
}
}
}

use GCJ::Cni;
use Matrix;

GCJ::Cni::JvCreateJavaVM(undef);
GCJ::Cni::JvAttachCurrentThread(undef, undef);

my $matrix = new Matrix::Matrix(10, 10);
populate_matrix($matrix);
my $matrix2 = new Matrix::Matrix(10, 10);
populate_matrix($matrix2);
$matrix3 = $matrix->multiply($matrix2);
$matrix3->print();

GCJ::Cni::JvDetachCurrentThread();

Ill leave it up to the reader to write a Perl module that does the same thing, that is, spawns 100 threads. In my own personal fiddling I found that just spawning that many threads (never mind doing any kind of work) was over 3 time slower in Perl. In this situation we at least get to use our favorite language, Perl, and offload some of the heavy hitting to a language more suited for it.

Where this really comes in handy is when you have an existing multi-threaded Java library that you would like to expose to Perl. You could theoretically natively compile various components of your library and then generate Perl bindings to access it. In this way, you get a little extra speed and efficiency as well as code reuse and binding.

Java::JCR::Workspace is a Perl wrapper for javax.jcr.Workspace.
This is an automatically generated package wrapping javax.jcr.Workspace with a nice Perlish API.
For full documentation of what this class does, see the Java API documentation: http://www.day.com/maven/jsr170/javadocs/jcr-1.0/javax/jcr/Workspace.html
The deviations from the API documentation include the following:
- You will need to use Perl, intead of Java, to make any use of this API. (Duh.)
The package to use is Java::JCR::Workspace, rather than javax.jcr.Workspace.
- All method names have been changed from Java-style camelCase() to Perl-style lower_case().
Thus, if the function were named getName() in the Java API, it will be named get_name() in this API. As another example, nextEventListener() in the Java API will be next_event_listener() in this API.
- Handle exceptions just like typical Perl. Java::JCR::Exception takes care of making sure that works as expected.

Java::JCR::Lock is a Perl module that can load JCR lock extension wrappers.

SYNOPSIS

use Java::JCR::Lock

This loads the Perl classes mapped to the Java package named javax.jcr.lock.

Installation:

Installation can be a bit tricky because this library depends upon Inline::Java,
which didnt install without going through the process by hand. (I usually just
let CPAN do all the work.) You must first install Inline::Java.

Then, you must install libwww-perl, as I use that to download the Jar files. I
hope to remove this dependency in the future, but its there for now.

After installing both of those, you should be able to run:

perl Build.PL
./Build
./Build test
./Build install

I generally try to make my build scripts as standard as possible. If you prefer
using make, I have Module::Build distributing a makefile generator too:

perl Makefile.PL
make
make test
make install

Java Properties provides an efficient way to access bean-like properties of Java objects.

In a nutshell, provides an efficient way to access bean-like properties of java objects. Unlike java bean properties, a chain of properties can be specified efficiently, allowing convenient access to properties of nested domain objects.

Runtime class-generation and caching can be used very easily to obviate the need for reflection, without losing the flexibility it provides.

Class Properties It also provides classes which manipulate objects at runtime by using strings to address conceptual variables (think bean properties) in a similar fashion to the java reflection mechanisms.

Class Property example Say we have the following classes:

public class Order {
...
public Customer getCustomer() { ... }
...
}
public class Customer {
...
public Address getAddress() { ... }
...
}
public class Address {
...
public String getLine1() { ... }
public String getLine2() { ... }
...
}

Now, we could do this to access line 1 of the address:

result = order.getCustomer().getAddress().getLine1();

But what if there are nulls? What if we want to compare the first line of the address from two different orders? Whith properties this is really simple:

ClassProperty p = PropertyManager.getProperty(Order.class,"Customer:Address:Line1",true);
result = p.getValue(order);

The idea is simple enough - you use the string "Customer:Address:Line1" to specify a series of getXXX calls. Importantly, it the library handles nulls for you, returning null if any of the objects in the chain are null.

Note, this is not simply a wrapper around java reflection, since it includes non-reflective optimizations by making use of the cojen library to generate class files at runtime to acces these properties.

The real benefit lies in being able to specify which properties you wish to access at runtime. You can even pass this ability on to the users of your library or application. Unlike reflection, class files are generated for the properties, and these files are cached - which means once you have specified a property once, further uses of the same property dont use reflection and are very fast.

Property API vs Java Bean Properties. The property API models accessor/mutator method pairs as conceptual variables called properties. The approach used is similar to, but more flexible than java bean properties, and more performant than reflection if runtime class generation is used. Unlike java bean properties, a chain or path of properties can be specified (and more importantly, turned into bytecode using runtime generation) to traverse a complex tree of objects.
It is simple to create applications portable between different security environments - using runtime generation where allowed, and falling back to reflection where security is tighter.

Dynamic Class Management. The properties package also provides classes to handle the loading (and unloading/reloading) of classes at runtime. It provides a framework useful for dynamically loading runtime-generated classes, for example.
While the property API can happily ignore the dynamic loading framework, it can also make use of it to enable runtime class generation.