import java.io.FileInputStream;

/** HistoryFactsFile abstract class
 Object of this type are meant to encapsulate the actual source and stream 
 from which the data comes. Methods are provided for clients to get information 
 * from the object.
 *
Concrete implementations should provide a constructor which opens a data source
 (such as a file) containing history information. 

 * In project 2, because of the file format, clients should call
 * nextDate and nextFact in strict alternation.  The implementation
 * is not required to enforce this.
 *
 * For Project 2, only ASCII text files need be processed.   The required format
 * of those files is given in the project description.
 * However, there is nothing in the abstract class that requires such a format.
 */
public abstract class HistoryFactsFile {
    
        /** Changes from the original spec:  the instannce variable is now private,
         * and is named dataSourceName instead of fileName
         */
    protected String dataSourceName = "no file yet";
    
        /** Change from the original spec: this instance variable removed.
         */
    //protected FileInputStream fileStream = null; 
    
    /**returns false if no more data is available; true otherwise
    */
    public abstract boolean hasNext( ); 
    
    /** After calling nextDate, a client should call nextFact before calling nextDate again
     */
    public abstract String nextDate( ); //returns the next date line on the file
     
    /** After calling nextFact, a client should call nextDate before calling nextDate again
     */     
    public abstract String nextFact( ); //returns the next fact line on the file
}