Node:Jasper Method Call Example, Next:, Up:The Jasper Library


Jasper Method Call Example

We begin with a small example. 

                             
// Simple.java


import se.sics.jasper.*;

public class Simple {
  private String instanceDatum = "this is instance data";

  static int simpleMethod(int value) {
    return value*42;
  }

  public String getInstanceData(String arg) {
    return instanceDatum + arg;
  }
}

Compile Simple.java (UNIX): 

% javac -deprecation \
  -classpath <installdir>/lib/sicstus-3.12.0/bin/jasper.jar Simple.java

Under Windows this may look like (the command should go on a single line): 

C:\> c:\jdk1.2.2\bin\javac -deprecation
 -classpath "D:\Program Files\SICStus Prolog 3.12.0\bin\jasper.jar" Simple.java

The option -deprecation is always a good idea, it makes javac warn if your code use deprecated methods. 

                                
% simple.pl


:- use_module(library(jasper)).
main :-
   %% Replace '/my/java/dir' below with the path containing
   %% 'Simple.class', e.g. to look in the current directory use
   %% classpath(['.']).
   %% You can also use the CLASSPATH environment variable and call
   %% jasper_initialize(JVM)
   %% Under Windows it may look like classpath(['C:/MyTest'])
   jasper_initialize([classpath(['/my/java/dir'])],JVM),

   format('Calling a static method...~n',[]),
   jasper_call(JVM,
               method('Simple','simpleMethod',[static]), % Which method
               simple_method(+integer,[-integer]), % Types of arguments
               simple_method(42,X)), % The arguments.
   format('simpleMethod(~w) = ~w~n',[42,X]),

   format('Creating an object...~n',[]),
   jasper_new_object(JVM, 'Simple', init, init, Object),

   format('Calling an instance method on ~w...~n',[Object]),
   jasper_call(JVM,
               method('Simple','getInstanceData',[instance]),
               %% first arg is the instance to call
               get_instance_data(+object('Simple'), +string,[-string]),
               get_instance_data(Object, 'foobar', X1)),
   format('getInstanceData(~w) = ~w~n',['foobar',X1]).

Then, run SICStus: 

% echo "[simple],main." | sicstus
SICStus 3.9 (x86-linux-glibc2): Fri Sep 24 17:43:20 CEST 1999
Licensed to SICS
% consulting /home1/jojo/simple.pl...
[...]
% consulted /home1/jojo/simple.pl in module user, 100 msec 26644 bytes
Calling a static method...
simpleMethod(42) = 1764
Creating an object...
Calling and instance method on $java_object(135057576)...
getInstanceData(foobar) = this is instance datafoobar

This example performed three things.