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/*
 * SymbolTable.java
 *
 * Created on November 19, 2001
 */

package com.sun.jdo.spi.persistence.support.ejb.ejbqlc;

import java.util.Map;
import java.util.HashMap;

/**
 * The symbol table handling declared identifies.
 *
 * @author  Michael Bouschen
 */
public class SymbolTable
{
    /**
     * The table of declared identifier (symbols).
     */
    protected Map symbols = new HashMap();

	/**
	 * This method adds the specified identifier to this SymbolTable. 
     * The specified decl object provides details anbout the declaration. 
     * If this SymbolTable already defines an identifier with the same name, 
     * the SymbolTable is not changed and the existing declaration is returned. 
     * Otherwise <code>null</code> is returned.
     * @param   ident   identifier to be declared
     * @param   definition new definition of identifier
     * @return  the old definition if the identifier was already declared; 
     * <code>null</code> otherwise
	 */
    public Object declare(String ident, Object decl)
    {
        Object old = symbols.get(ident);
        if (old == null) {
            symbols.put(ident.toUpperCase(), decl);
        }
        return old;
    }

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

    /**
     * Checks the symbol table for the actual declaration of the specified 
     * identifier. The method returns the declaration object if available or
     * <code>null</code> for an undeclared identifier. 
     * @param ident the name of identifier
     * @return the declaration object if ident is declared;
     * <code>null</code> otherise.
     */
    public Object getDeclaration(String ident)
    {
        return symbols.get(ident.toUpperCase());
    }
	
}