private double parseAtomElement() throws Exception {  
        double result = 0.0; //   
          
        switch (this.tokenType) {  
        case NUMBER_TOKEN:  
            // ǰΪ  
            try {  
                // ֵַתֵ  
                result = Double.parseDouble(this.token);  
            } catch (NumberFormatException exc) {  
                this.handleError(SYNTAX_ERROR);  
            }  
            this.getToken(); // ȡһ  
            break;  
        case VARIABLE_TOKEN:  
            // ǰǱȡֵ  
            result = MyMath.getFunctionValue(token);  
            this.getToken();  
            break;  
        default:  
            this.handleError(SYNTAX_ERROR);  
            break;  
        }  
        return result;  
    }