fieldinfo.java

已经移植好的java虚拟机

/*
 *	FieldInfo.java	1.7	99/04/06 SMI
 *
 * Copyright (c) 1997 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * Use is subject to license terms.
 */

package components;
import java.io.DataOutput;
import java.io.DataInput;
import java.io.IOException;
import java.util.Hashtable;
import util.DataFormatException;
import vm.Const;

/*
 * A Field of a class. Includes statics, static finals, and
 * of course instance fields.
 * In Java, we don't have enumerations, but we do have
 * static final fields, and these have a value attribute.
 */
public
class FieldInfo extends ClassMemberInfo {

    private Attribute 	  fieldAttributes[];
    public ConstantObject value;
    private ConstantValueAttribute  valueAttribute;
    public int		  instanceOffset = -1; // for instance fields only, of course
    public int  	  nSlots = -1;	     // ditto

    public
    FieldInfo( int name, int sig, int access, ClassInfo p ){
	super( name, sig, access, p );
    }

    /*
     * The only field attribute we care about is
     * the ConstantValue attribute
     */
    private static Hashtable fieldAttributeTypes = new Hashtable();
    static{
	fieldAttributeTypes.put("ConstantValue", ConstantValueAttributeFactory.instance );
    }

    // Read attributes from classfile
    private void
    readAttributes( DataInput in ) throws IOException {
	fieldAttributes = Attribute.readAttributes( in, parent.constants, parent.symbols, fieldAttributeTypes, false );
    }

    // Read field from classfile
    public static FieldInfo 
    readField( DataInput in, ClassInfo p ) throws IOException {
	int acc  = in.readUnsignedShort();
	int name = in.readUnsignedShort();
	int sig =  in.readUnsignedShort();
	FieldInfo fi = new FieldInfo( name, sig, acc, p );
	fi.readAttributes(in );
	fi.resolve( p.symbols );
	return fi;
    }

    public void resolve( ConstantObject table[] ){
	if ( resolved ) return;
	super.resolve( table );
	/*
	 * Parse attributes.
	 * If we find a value attribute, pick it out
	 * for special handling.
	 */
	if ( fieldAttributes != null ) {
	    for ( int i = 0; i < fieldAttributes.length; i++ ){
		Attribute a = fieldAttributes[i];
		if (a.name.string.equals("ConstantValue") ) {
		    valueAttribute = (ConstantValueAttribute)a;
		    value = valueAttribute.data;
		}
	    }
	}
	switch( type.string.charAt(0) ){
	case 'D':
	case 'J':
	    nSlots = 2; access |= Const.ACC_DOUBLEWORD; break;
	case 'L':
	case '[':
	    nSlots = 1; access |= Const.ACC_REFERENCE; break;
	default:
	    nSlots = 1; break;
	}
	resolved = true;
    }

    public void externalize( ConstantPool p ){
	super.externalize( p );
	Attribute.externalizeAttributes( fieldAttributes, p );
	if ( value != null ){
	    value = valueAttribute.data;
	}
    }

    public void
    countConstantReferences( boolean isRelocatable ){
	super.countConstantReferences();
	Attribute.countConstantReferences( fieldAttributes, isRelocatable );
    }

    public void
    write( DataOutput o ) throws IOException {
	o.writeShort( access );
	if ( resolved ){
	    o.writeShort( name.index );
	    o.writeShort( type.index );
	    Attribute.writeAttributes( fieldAttributes, o, false );
	} else {
	    o.writeShort( nameIndex );
	    o.writeShort( typeIndex );
	    o.writeShort( 0 ); // no attribute!
	}
    }

    public String toString(){
	String r = "Field: "+super.toString();
	if ( value != null ){
	    r += " Value: "+value.toString();
	}
	return r;
    }


}