public ExpressionNode parseExpression(String expr) {
if (operandFactory == null) {
operandFactory = new SimpleOperandFactory();
}
if (operations == null) {
operations = new SimpleOperandOperations();
}
if (!operatorStrings.contains("(")) { //$NON-NLS-1$
operatorStrings.add("("); //$NON-NLS-1$
}