treeprinter.java

Grammatica is a C# and Java parser generator (compiler compiler). It improves upon simlar tools (lik

/*
 * TreePrinter.java
 *
 * This work is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License,
 * or (at your option) any later version.
 *
 * This work is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 * USA
 *
 * As a special exception, the copyright holders of this library give
 * you permission to link this library with independent modules to
 * produce an executable, regardless of the license terms of these
 * independent modules, and to copy and distribute the resulting
 * executable under terms of your choice, provided that you also meet,
 * for each linked independent module, the terms and conditions of the
 * license of that module. An independent module is a module which is
 * not derived from or based on this library. If you modify this
 * library, you may extend this exception to your version of the
 * library, but you are not obligated to do so. If you do not wish to
 * do so, delete this exception statement from your version.
 *
 * Copyright (c) 2003 Per Cederberg. All rights reserved.
 */

package net.percederberg.grammatica;

import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.Writer;

import net.percederberg.grammatica.parser.Analyzer;
import net.percederberg.grammatica.parser.Node;

/**
 * A parse tree printer. This class prints the parse tree while it is
 * being parsed. 
 *
 * @author   Per Cederberg, <per at percederberg dot net>
 * @version  1.4
 * @since    1.4
 */
public class TreePrinter extends Analyzer {

    /**
     * The current indentation level.
     */
    private int indentation = 0; 

    /**
     * The output stream to use.
     */
    private PrintWriter output;

    /**
     * Creates a new parse tree printer.
     * 
     * @param output         the output stream to use
     */
    public TreePrinter(OutputStream output) {
        this(new PrintWriter(output));
    }

    /**
     * Creates a new parse tree printer.
     * 
     * @param output         the output stream to use
     */
    public TreePrinter(Writer output) {
        if (output instanceof PrintWriter) {
            this.output = (PrintWriter) output;
        } else {
            this.output = new PrintWriter(output);
        }
    }

    /**
     * Called when entering a parse tree node. By default this method
     * does nothing. A subclass can override this method to handle 
     * each node separately.  
     * 
     * @param node           the node being entered
     */
    protected void enter(Node node) {
        for (int i = 0; i < indentation; i++) {
            output.print("  ");
        }
        output.println(node.toString());
        output.flush();
        indentation++;
    }

    /**
     * Called when exiting a parse tree node. By default this method
     * returns the node. A subclass can override this method to handle 
     * each node separately. If no parse tree should be created, this 
     * method should return null.
     * 
     * @param node           the node being exited
     * 
     * @return the node to add to the parse tree, or
     *         null to remove the node
     */
    protected Node exit(Node node) {
        indentation--;
        return null;
    }
}