hashcomment.java

JAVA在编译原理上的应用。

package lolo.scans;

/** A recognizer class to scan for hash comments: all characters from <tt>#</tt> up to EOL. 
 * <p>By default these symbols will be ignored.
 *
 * @author <a href="http://www.inf.uos.de/bernd" target="_blank">Bernd K&uuml;hl</a>
           (<a href="mailto:[e-mail]">[e-mail]</a>)
 */
public class HashComment extends SlashSlashComment {
    /** The legal characters. */ // A means ANY
    protected static final String chars = "A#\r\n";
    /** The state table. */
    protected static final int newState [][] = {
        // current state, input => newstate
        // ANY  #  \r   \n
        {  3,   1,  3,  3   },  // state 0, find #
        {  1,   1,  2,  2   }   // state 1, okay and need more characters
                                // state 2, comment found
                                // state 3, error
    };
    public State nextChar(char ch) {
        // is ch a legal input character?
        int input = chars.indexOf(ch);
        if (input < 0) input = 0;
        
        boolean found = false, more = false;
        state = newState[state][input];
        switch(state) {
            case 3:	 break;    // error state, parse ends
            case 0:	 new RuntimeException("illegal state "+state); // cann't be..
            case 1:	 more = true; break;
            case 2:	 found = true; break;
            default: new RuntimeException("illegal state "+state); // cann't be..
        }
        
        return stateObject.set(more, found);
    }
}