OpenJava Tutorial

6. Callee-side Translation

In this section, an example of simple translation at callee-side is described.

6.1. What the base-level program should look like

Most of example programs given in the text are ready to be executed by the OpenJava system and are similar in form to:

import java.util.*;
public class StringCollection instantiates FreeArgsClass
{
    Vector contents = new Vector();
    public generous void addAll( String[] args ) {
        for (int i = 0; i < args.length; ++i)  contents.addElement( args[i] );
    }
}

public class Test
{
    void test() {
        StringCollection strs = new StringCollection();
        strs.addAll( "one", "two", "three" );
    }
}

6.2. What the base-level program should be translated

Like following:

public class Test
{
    void test() {
        StringCollection strs = new StringCollection();
        strs.addAll( new String[]{ "one", "two", "three" } );
    }
}

6.3. Write a meta-level program

import openjava.mop.*;
import openjava.ptree.*;
import openjava.syntax.*;

public class FreeArgsClass instantiates Metaclass extends OJClass
{
    private static final String GENEROUS = "generous";
    /** Translates definition */

    public void translateDefinition() throws MOPException {
        OJMethod[] methods = getDeclaredMethods();
        for (int i = 0; i < methods.length; ++i) {
            if (! methods[i].getModifiers().has( GENEROUS ))  continue;
            System.err.println( methods[i] );
            OJClass[] paramtypes = methods[i].getParameterTypes();
            if (paramtypes.length != 1 || ! paramtypes[0].isArray()) {
                System.err.println( "illegal parameter, ignored." );
                continue;
            }
            putMetaInfo( methods[i].getName(), paramtypes[0].getName() );
        }
    }

    public OJMethod resolveException( NoSuchMemberException e,
                                      String name, OJClass[] params )
        throws NoSuchMemberException
    {
        try {
            String argtypename = getMetaInfo( name );
            if (argtypename != null) {
                OJClass paramtype = OJClass.forName( argtypename );
                return getMethod( name, new OJClass[]{ paramtype }, this );
            }
        } catch ( OJClassNotFoundException e2 ) {
            System.err.println( e2 );
        }
        return super.resolveException( e, name, params );
    }

    /** Translates allocation parts */
    public Expression expandMethodCall( Environment env, MethodCall expr ) {
        String argtypename = getMetaInfo( expr.getName() );
        if (argtypename == null)  return expr;
        OJClass comptype;
        try {
            comptype = OJClass.forName( argtypename ).getComponentType();
        } catch ( OJClassNotFoundException e ) {
            System.err.println( e );
            return expr;
        }
        ExpressionList dim = new ExpressionList( null );
        ArrayInitializer ainit = new ArrayInitializer( expr.getArguments() );
        ArrayAllocationExpression carrier
          = new ArrayAllocationExpression( comptype, dim, ainit );
        expr.setArguments( new ExpressionList( carrier ) );
        return expr;
    }

    public static boolean isRegisteredModifier( String keyword ) {
        if (keyword.equals( GENEROUS ))  return true;
        return false;
    }