/*
 *    ConstantObject.java    1.4    99/04/06 SMI
 *
 * Copyright © 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

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

/*
 * An abstract class for representing objects in the constant pools
 * All constants are derived from here.
 * Note how this and all its derivatives are Cloneable.
 */

public
abstract class ConstantObject extends ClassComponent implements Cloneable
{
    public int references = 0;
    public int ldcReferences = 0;
    public boolean shared = false;
    public ConstantPool containingPool; // if shared == true, then container.

    public int index;

    // The type of constant pool entry.
    public int tag;

    // The number of slots this thing "uses" -- usually 1, sometimes 2
    public int nSlots;

    public void incldcReference() {
        ldcReferences++;
    }

    public void decldcReference() {
        ldcReferences--;
    }
 
    public void clearldcReference(){
        ldcReferences = 0;
    }

    // Some items are reference counted so that the most frequently
    // accessed ones can be placed in the first 256 entries of the
    // constant table.  Others are just marked as used so we know
    // to include them somewhere in the table.
    public void incReference() {
    references++;
    }

    public void decReference() {
    references--;
    }

    public void clearReference(){
    references = 0;
    }

    public Object clone(){
    ConstantObject newC;
    try {
        newC = (ConstantObject)super.clone();
        newC.references = 0;
        newC.shared     = false;
        newC.index      = 0;
        return newC;
    } catch( CloneNotSupportedException e ){
        e.printStackTrace();
        System.exit(1);
    }
    return null;
    }

    public abstract boolean isResolved();

    static public ConstantObject readObject( DataInput i ) throws IOException{
    // read the tag and dispatch accordingly
    int tag = i.readUnsignedByte();
    switch( tag ){
    case Const.CONSTANT_UTF8:
        return UnicodeConstant.read( tag, i );
    case Const.CONSTANT_INTEGER:
    case Const.CONSTANT_FLOAT:
        return SingleValueConstant.read( tag, i );
    case Const.CONSTANT_DOUBLE:
    case Const.CONSTANT_LONG:
        return DoubleValueConstant.read( tag, i );
    case Const.CONSTANT_STRING:
        return StringConstant.read( tag, i );
    case Const.CONSTANT_NAMEANDTYPE:
        return NameAndTypeConstant.read( tag, i );
    case Const.CONSTANT_CLASS:
        return ClassConstant.read( tag, i );
    case Const.CONSTANT_FIELD:
        return FieldConstant.read( tag, i );
    case Const.CONSTANT_METHOD:
        return MethodConstant.read( tag, i );
    case Const.CONSTANT_INTERFACEMETHOD:
        return InterfaceConstant.read( tag, i );
    default:
        throw new DataFormatException("Format error (constant tag "+tag+" )");
    }
    }
}