Function Dictionary

By default, EvalEx has its own dictionary for the operators that can be used in an expression, the MapBasedOperatorDictionary. It stores and retrieves the operators in a case-insensitive TreeMap.

You can easily define your own operator directory, by defining a class that implements the FunctionDictionaryIfc:

public interface OperatorDictionaryIfc {

  /**
   * Allows to add an operator to the dictionary. Implementation is optional, if you have a fixed
   * set of operators, this method can throw an exception.
   *
   * @param operatorString The operator name.
   * @param operator The operator implementation.
   */
  void addOperator(String operatorString, OperatorIfc operator);

  /**
   * Check if the dictionary has a prefix operator with that name.
   *
   * @param operatorString The operator name to look for.
   * @return <code>true</code> if an operator was found or <code>false</code> if not.
   */
  default boolean hasPrefixOperator(String operatorString) {
    return getPrefixOperator(operatorString) != null;
  }

  /**
   * Check if the dictionary has a postfix operator with that name.
   *
   * @param operatorString The operator name to look for.
   * @return <code>true</code> if an operator was found or <code>false</code> if not.
   */
  default boolean hasPostfixOperator(String operatorString) {
    return getPostfixOperator(operatorString) != null;
  }

  /**
   * Check if the dictionary has an infix operator with that name.
   *
   * @param operatorString The operator name to look for.
   * @return <code>true</code> if an operator was found or <code>false</code> if not.
   */
  default boolean hasInfixOperator(String operatorString) {
    return getInfixOperator(operatorString) != null;
  }

  /**
   * Get the operator definition for a prefix operator name.
   *
   * @param operatorString The name of the operator.
   * @return The operator definition or <code>null</code> if no operator was found.
   */
  OperatorIfc getPrefixOperator(String operatorString);

  /**
   * Get the operator definition for a postfix operator name.
   *
   * @param operatorString The name of the operator.
   * @return The operator definition or <code>null</code> if no operator was found.
   */
  OperatorIfc getPostfixOperator(String operatorString);

  /**
   * Get the operator definition for an infix operator name.
   *
   * @param operatorString The name of the operator.
   * @return The operator definition or <code>null</code> if no operator was found.
   */
  OperatorIfc getInfixOperator(String operatorString);
}

Only four methods need to be implemented:

• addOperator(String operatorString, OperatorIfc operator) - which allows to add an operator.
• OperatorIfc getPrefixOperator(String operatorString) - retrieves a prefix operator.
• OperatorIfc getPostfixOperator(String operatorString) - retrieves a postfix operator.
• OperatorIfc getInfixOperator(String operatorString) - retrieves a infix operator.

The addOperator() method is only called when an operator is added to the configuration, using the withAdditionalOperators() in the ExpressionConfiguration object.

NOTE: The operator names that are passed to the methods are case-sensitive, just like they were entered in the expression.

The custom operator dictionary can then be specified in the expression configuration:

ExpressionConfiguration configuration = ExpressionConfiguration.builder()
    .operatorDictionary(new MyOperatorDictionary())
    .build();