package com.wutka.dtd;import java.io.*;/** Represents an external ID in an entity declaration * * @author Mark Wutka * @version $Revision: 1.16 $ $Date: 2002/07/19 01:20:11 $ by $Author: wutka $ */public abstract class DTDExternalID implements DTDOutput{    public String system;    public DTDExternalID()    {    }/** Writes out a declaration for this external ID */    public abstract void write(PrintWriter out)        throws IOException;        public boolean equals(Object ob)    {        if (ob == this) return true;        if (!(ob instanceof DTDExternalID)) return false;        DTDExternalID other = (DTDExternalID) ob;        if (system == null)        {            if (other.system != null) return false;        }        else        {            if (!system.equals(other.system)) return false;        }        return true;    }/** Sets the system ID */    public void setSystem(String aSystem)    {        system = aSystem;    }/** Retrieves the system ID */    public String getSystem()    {        return system;    }}