Nondrawable Java Export Example

Nondrawable objects provide access to the enormous processing power of IDL, but do not provide IDL drawing capabilities. This is useful for applications that need the data manipulation capabilities of IDL, but have no need for, or have independent drawing capabilities.

Hello World Java Example with Additional Method

The following simple example creates an IDL object with a single function method that accepts one argument, and walks through the process of exporting the object using the Export Bridge Assistant. Once the export files are created, a simple Java application shows how to access the object method and capture its output.

In an IDL Editor window, copy in the following code and save the file as helloworldex__define.pro in your working directory:

  
; Method returns message based on presence or   
; absence of argument.  
FUNCTION helloworldex::HelloFrom, who  
      IF (N_ELEMENTS(who) NE 0) THEN BEGIN  
      message = "Hello World from " + who  
      RETURN, message  
   ENDIF ELSE BEGIN  
      message = 'Hello World'  
      RETURN, message  
   ENDELSE  
END  
  
; Init returns object reference on successful  
; initialization.  
FUNCTION helloworldex::INIT  
   RETURN, 1  
END  
  
; Object definition.  
PRO helloworldex__define  
  struct = {helloworldex, $  
     who: '' , $  
     message: ' ' $  
  }  
END

Note
It is a good idea to test the functionality of an object before exporting it. After compiling the file, enter the following lines at the command line and make sure the output is what is expected for this object.

ohello = OBJ_NEW("HELLOWORLDEX")

PRINT, ohello->HelloFrom()

PRINT, ohello->HelloFrom('Mr. Bill')

Open the Export Bridge Assistant by entering IDLEXBR_ASSISTANT at the command line.

Select to create a Java export object by selecting File

New Project

Java and browse to select the helloworldex__define.pro file. Click Open to load the file into the Export Assistant.

Note
Export Bridge Assistant details are available in Specifying Information for Exporting. Refer to that section if you need more information about the following steps.

The top-level project entry in the left-hand tree panel is selected by default. There is no need to modify the default properties shown in the right-hand property panel, but you can enter different values if desired. Set other export object characteristics as described in the following table. Select the tree view item listed in the left column to configure the related properties in the right column.

Table 13-1: Example Export Object Parameters

Table 13-1: Example Export Object Parameters
Tree View Item	Parameter Configuration
IDL Export Bridge Project	Accept the default value or make changes: Output classname Process name Output directory
helloworldex	Drawable object equals False
Package name	helloworldex
HELLOFROM method	Output method name — accept the default value, HELLOFROM Return Type — JIDLString since this function method returns a string message (as defined in the IDL object definition structure) Array — False since this method returns a single string, not an array Export — True
WHO argument	Mutability — In since the argument is not passed back to the caller Type — JIDLString since this argument is defined as a string in the IDL object definition Array — False Export — True

Save the project by selecting File

Save project. Accept the default name and location or make changes as desired.

Verify that the object elements you want to export are listed in the Export log panel. If the expected items are not present, one or more items may still have an UNSPECIFIED field value that must be changed.

Build the export object by selecting Build

Build object. The Build log panel shows the results of the build process. A subdirectory, named helloworldex (based on the object name), contains the .java and .class files, and is located in the Output directory.

Using the Export Wrapper Object

The following simple Java application uses the wrapper object created in the previous section.

Open the file named helloworldex_example.java in the previously referenced directory and save the file in the helloworldex directory.

Open the Windows Command window by selecting Start

Run and enter cmd in the textbox.

Use the cd command to change to the directory containing the helloworldex directory.

Reference the classpath of javaidlb.jar in the compile statement. Enter the following two commands (as single lines) to compile and execute the program, replacing IDL_DIR with the IDL installation directory:

javac -classpath 
   ".;IDL_DIR\resource\bridges\export\java\javaidlb.jar"  
   helloworldex\helloworldex_example.java  
java -classpath 
   ".;IDL_DIR\resource\bridges\export\java\javaidlb.jar"  
   helloworldex.helloworldex_example

Tip
See Note on Running the Java Examples for information on executing Java commands on a non-Windows platform.

After compiling and running the project, the output message will appear in the command window.