/**

   A boolean variable is a lowercase letter
   
*/

public class BooleanVariable extends BooleanExpression {

    private static HashTable<Character,Boolean> values =
	new HashTable<Character,Boolean>();


    public BooleanVariable (char varname) {
	// @@@ STUB.. to do:  if the variable doesn't exist yet
	// in the hash table, then insert it with the default value
	// of true.  If it does exist, let it keep its current value
    }

    public BooleanVariable (char varname, boolean value) {
	// @@@ STUB.. to do:  if the variable doesn't exist yet
	// in the hash table, then insert it with the value given.
	// If it does exist, and the value given is consistent with the
	// current value no problem.
	// otheriwse, there is a conflict--in that case,
	//    throw new IllegalArgumentException(""); 
    }

    // As variables are encountered, they are added to the hashtable.
    // It's static because we want the variable p to always have the same
    // value no matter where it appears in the expression.

    /** set the value of a variable

	@param varname the variable to set (e.g. 'p')
	@param newValue the new value to give it (true or false)

    */

    public static setValue(char varname, boolean newValue) {
	// @@ STUB.. figure out if varname is in the hash table
	// as a key.  If so, change its value to newValue.
	// If it isn't, then you can insert it into the hashtable
	// with the new value. 
	
    }
    
    private char variableName = 'p';

    /**
       look up the value of this variable and return it 
    */

    public boolean getValue() {
	return values.get(variableName);
    }

    /**
       
     */
    public String toString() {
	return Character.toString(variableName);
    }

}