Implementation

Below is a partial implementation of the scanner. Assume for now that there is a method read() which gets the next character from the input file, and puts it in an int. If the end of the file has been reached, it returns -1. The program needs to convert this int to a char. Look at the red code to see how this is done. Also, let us continue the assumption that any character less than space counts as white space. Check that each transition in the diagram is included in the code.

  public String getURL() throws IOException
  {
    final char space = ' ';
    String buffer = null;   // buffer for the URL 
    int  state = 0;         // the current state
    int  readInt;           // value returned by read()
    char current;           // the current character

    while ( (readInt=in.read()) != -1 )
    {
      current = (char)readInt;

      if      ( state==0 && (current == 'H' || current == 'h') )
        state = 1;
      else if ( state==0 )      
        state  = 0; 
 
      else if ( state==1 && (current == 'T' || current == 't') )
        state = 2;
      else if ( state==1 )      
        state  = 0; 
 
      else if ( state==2 && (current == 'T' || current == 't') )
        state = 3;
      else if ( state==2 )      
        state  = 0; 
 
      else if ( state==3 && (current == 'P' || current == 'p') )
        state = 4;
      else if ( state==3 )      
        state  = 0; 
 
      else if ( state==4 && current == ':' )
        state = 5;
      else if ( state==4 )      
        state  = 0; 
 
      else if ( state==5 && current == '/' )
        state = 6;
      else if ( state==5 )      
        state  = 0; 
 
      else if ( state==6 && current == '/' )
      {
        state  = 7;
        buffer =   ; // init buffer
      }
      else if ( state==6 )      
        state  = 0; 
 
      else if ( state==7 && current > space  )
      {
        state  = 7;
        buffer +=  ; // append current character to buffer
      }
 
      else if ( state==7 )
        return   ;
    }

    return null;

  }

When called by another method, getURL() returns a string containing the next URL (if there is one) or null if it has scanned past the end of the file.

Answer:

Implementation

QUESTION 9: