Java Support - Getting Started

This document describes step-by-step how to start using STX:LIBJAVA. You need a running Smalltalk/X environment installed on your machine. For download and installation notes refer to Section Installation & Configuration.

Hello World! Example

Preparing Java classe

In this short example, we will show how to initialize Java support, how load a Java class into Smalltalk/X environment and how to call methods on this class.

First, let's create a simple HelloWorld.java:

  
package stx.libjava.examples;

public class HelloWorld {
  public void sayHello(String name) {
    System.out.println("Hello " + name);
   }
  
  public static void main(String[] args) { 
    new HelloWorld().sayHello(args[0]);
  }
}

Compile it using standard javac:

  javac HelloWorld.java

Let's assume that resulting HelloWorld.class is in directory ~/libjava-example-1/stx/libjava/examples. Therefore, the classpath one would use to run it under standard JVM would be ~/libjava-example-1.



Initializing Java support


  In order to run Java code within Smalltalk/X, Java support must be properly 
  initialized. This includes initialization of STX:LIBJAVA's runtime support 
  stuctures as well as initialization of some essential Java objects such as
  java.lang.Object, java.lang.System, standard I/O 
  streams, system properties etc. Standard JVM does this too before dispatching
  to any user code. 


To initialize STX:LIBJAVA and required Java classes, evaluate following code 
  in Workspace:


  
  Java initialize.
  JavaVM initializeVM.


  
  At this point, Java runtime is initialized and ready to run user code 
  (*). If you 
  look at terminal output Smalltalk/X VM, you may see number of info messages
  as STX:LIBJAVA loads and initializes Java classes. If the initialization does
  not proceed, check its configuration (see Section 
  Configuration), especially 
  if the Java release and JAVA_HOME are properly set.


Loading and running HelloWorld


  As with standard JVM, STX:LIBJAVA must be told where to look for compiled classes.
  A class path could be defined in user preferences (see Section 
  Configuration) or ad-hoc using 
  API method #addToClassPath:. The argument is path to directory
  or .jar file containing the classes - same path you would use with
  standard JVM. Assuming the compiled HelloWorld class is located under
  ~/libjava-example-1, evaluate:


  
  Java addToClassPath: '~/libjava-example-1'.



  Note, that now the Java is booted and running so we have just changed
  the classpath in living system.
  


  Now everything is ready to run the code. Evaluate:


  
  JAVA stx libjava examples HelloWorld main: #('World from Java running in ST/X').



  The first part -- JAVA org example HelloWorld -- accesses the
  Java class from Smalltalk. The class is loaded if not already. Sending 
  #main: invokes HelloWorld's public static void
  main(String[] args). Note, that here you pass a Smalltalk array
  with Smalltalk string - STX:LIBJAVA interoperability features handle this
  and automagically convert parameters to the form expected by Java code. 
  For details, refer SectionJava-Smalltalk 
  interoperability



  If everything went well, you should see a greeting in system 
  Transcript. 


Comments


Reinitializing Java runtime.

  If you want (for whatever reason - for example you have modified some STX:LIBJAVA
  internal classes and Java runtime become completely messed up) - you may always
  completely flush all Java classes and start over. To do so, evaluate:


  
  Java flushAllJavaResources.



  Then, initialize Java runtime as usual.



  






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