ccomment.java

JAVA在编译原理上的应用。

package lolo.scans;

/** A recognizer class to scan for (optional nested) C comments. 
 * <p>By default <tt>CComment</tt> 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 CComment extends SlashSlashComment {
    /** Scan for nested comments? */
    protected final boolean nested;
    /** Counts the number of open and nested comments. */
    protected transient int numberOpenComments;
    
    /** Constructs a recognizer which scans for unnnested C comments. */
    public CComment() {
        this(false);
    }

    /** Constructs a recognizer which scans for C comments.
     * If <tt>nested</tt> is <tt>true</tt>, the recognizer scans for nested comments.
     * 
     * @param nested marks if the recognizers scans nested comments.
     */
    public CComment(boolean nested) {
        this.nested = nested;
    }
    
    public void reset() {
        state = numberOpenComments = 0;
    }

    /** The legal characters. */ // A means ANY
    protected static final String chars = "A*/";
    /** The state table. */
    protected static final int newState [][] = {
	// current state, input -> newstate
	// ANY  *   /  
	{  7,   7,  1   },  // state 0, find /
	{  7,   2,  7   },  // state 1, find * for /*
	{  2,   5,  3   },  // state 2, find * for */ or / for nested /*
	{  2,   4,  3   },  // state 3, find * for nested /*
	{  2,   5,  3   },	// state 4, find * for */ or / for nested /*
	{  2,   5,  6   }	// state 5, find / for */
	                    // state 6, comment end found, check open comment count for end
	                    // state 7, 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;
        if (state == 1 && newState[state][input] == 2)
            numberOpenComments++;	// found /*
        state = newState[state][input];
        switch(state) {
            case 7:	break;    // error state, parse ends
            case 0:	new RuntimeException("illegal state "+state); // cann't be..
            case 1: //	/
            case 2:	//	/* ...
            case 3:	//	/* ... /
            case 5:	// /* .... *
                    more = true; break;
            case 4:	// /* ... /*
                    numberOpenComments++;
                    more = true; break;
            case 6:	// /* */
                    numberOpenComments--;
                    if (nested && numberOpenComments > 0) {
                        more = true;
                        state = 2; // find * for */
                    } else
                        found = true;
                    break;
            default: new RuntimeException("illegal state "+state); // cann't be..
        }
        
        return stateObject.set(more, found);
    }
    
    /** Returns a string representation.
     *
     * @return a string representation.
     */
    public String toString() {
        return getClass().getName()+(nested ? "[nested]" : "");
    }
}