Glassfish example source code file (SymbolTable.java)

This example Glassfish source code file (SymbolTable.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Glassfish tags/keywords

definition, definition, hashtable, hashtable, iterator, iterator, nesting, stack, stack, string, symboltable, util

The Glassfish SymbolTable.java source code

/*
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 *
 * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
 *
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 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
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 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
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 * and therefore, elected the GPL Version 2 license, then the option applies
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 */

/*
 * SymbolTable.java
 *
 * Created on March 8, 2000
 */

package com.sun.jdo.spi.persistence.support.sqlstore.query.util.scope;

import java.util.Hashtable;
import java.util.Iterator;
import java.util.Stack;

/**
 * The symbol table handling declared identifies.
 *
 * @author  Michael Bouschen
 * @version 0.1
 */
public class SymbolTable
{
    /**
     * The actual scope level.
     */
    protected int actualScope = 0;
    
    /**
     * Stack of old definitions.
     */
    protected Stack nestings = new Stack();
    
    /**
     * The table of declared identifier (symbols).
     */
    protected Hashtable symbols = new Hashtable();

    /**
     * Opens a new scope. 
     * Prepare everything to handle old definitions when 
     * a identifier declaration is hidden.
     */
    public void enterScope()
    {
        actualScope++;
        nestings.push(new Nesting());
    }

    /**
     * Closes the actual scope.
     * Hidden definitions are reinstalled.
     */
    public void leaveScope()
    {
        forgetNesting((Nesting)nestings.pop());
        actualScope--;
    }

    /**
     * Returns the level of the actual scope.
     * @return actual scope level.
     */
	public int getActualScope()
	{
		return actualScope;
	}
	
	/**
	 * Add identifier to the actual scope.
     * If the identifier was already declared in the actual
     * scope the symbol table is NOT changed and the old definition
     * is returned. Otherwise a possible definition of a lower 
     * level scope is saved in the actual nesting and the new definition 
     * is stored in the symbol table. This allows to reinstall the old
     * definition when the sctaul scope is closed.
     * @param   ident   identifier to be declared
     * @param   def new definition of identifier
     * @return  the old definition if the identifier was already declared 
	 *          in the actual scope; null otherwise
	 */
    public Definition declare(String ident, Definition def)
    {
        Definition old = (Definition)symbols.get(ident);
        def.setScope(actualScope);
        if ((old == null) || (old.getScope() < actualScope))
        {
            Nesting nest = (Nesting)nestings.peek();
            nest.add(ident, old); // save old definition in nesting
            symbols.put(ident, def); // install new definition as actual definition
			return null;
        }
        else
        {
            return old;
        }
    }

    /**
     * Checks whether the specified identifier is declared.  
     * @param ident the name of identifier to be tested
     * @return true if the identifier is declared; 
     * false otherwise.
     */
    public boolean isDeclared(String ident)
    {
        return (getDefinition(ident) != null);
    }

    /**
     * Checks the symbol table for the actual definition 
     * of the specified identifier. If the identifier is 
     * declared the definition is returned, otherwise null.
     * @param ident the name of identifier
     * @return the actual definition of ident is declared;
     * null otherise.
     */
    public Definition getDefinition(String ident)
    {
        return (Definition)symbols.get(ident);
    }
	
    /**
     * Internal method to reinstall the old definitions. 
     * The method is called when a scope is closed. 
     * For all identifier that were declared in the 
     * closed scope their former definition (that was hidden) 
     * is reinstalled.
     * @param nesting list of hidden definitions
     */
    protected void forgetNesting(Nesting nesting)
    {
        String ident = null;
        Definition hidden = null;

        Iterator idents = nesting.getIdents();
        Iterator hiddenDefs = nesting.getHiddenDefinitions();

        while (idents.hasNext())
        {
            ident = (String) idents.next();
            hidden = (Definition) hiddenDefs.next();
            if (hidden == null)
            {
                symbols.remove(ident);
            }
            else
            {
                symbols.put(ident, hidden);
            }
        }
    }
}