/**
* Parses the expression. If there are errors in the expression, they are added to the <code>
* errorList</code> member. Errors can be obtained through <code>getErrorInfo()</code>.
*
* @param expression_in The input expression string
* @return the top node of the expression tree if the parse was successful, <code>null</code>
* otherwise
*/
public Node parseExpression(String expression_in) {
Reader reader = new StringReader(expression_in);
try {
// try parsing
errorList.removeAllElements();
topNode = parser.parseStream(reader, this);
// if there is an error in the list, the parse failed
// so set topNode to null
if (hasError()) topNode = null;
} catch (Throwable e) {
// an exception was thrown, so there is no parse tree
topNode = null;
// check the type of error
if (e instanceof ParseException) {
// the ParseException object contains additional error
// information
errorList.addElement(((ParseException) e).getMessage());
// getErrorInfo());
} else {
// if the exception was not a ParseException, it was most
// likely a syntax error
if (debug) {
System.out.println(e.getMessage());
e.printStackTrace();
}
errorList.addElement("Syntax error");
}
}
// If traversing is enabled, print a dump of the tree to
// standard output
if (traverse && !hasError()) {
ParserVisitor v = new ParserDumpVisitor();
try {
topNode.jjtAccept(v, null);
} catch (ParseException e) {
errorList.addElement(e.getMessage());
}
}
return topNode;
}
/**
* Evaluates and returns the value of the expression as an object. The EvaluatorVisitor member ev
* is used to do the evaluation procedure. This method is useful when the type of the value is
* unknown, or not important.
*
* @return The calculated value of the expression if no errors occur. Returns null otherwise.
*/
public Object getValueAsObject() {
Object result;
if (topNode == null) return null;
// evaluate the expression
try {
result = ev.getValue(topNode, symTab);
} catch (ParseException e) {
if (debug) System.out.println(e);
errorList.addElement("Error during evaluation: " + e.getMessage());
return null;
} catch (RuntimeException e) {
if (debug) System.out.println(e);
errorList.addElement(e.getClass().getName() + ": " + e.getMessage());
return null;
}
return result;
}
