a fork of EvalEx by ezylang with a handful of breaking changes
zenfyr.dev
1---
2layout: default
3title: Operator Dictionary
4parent: Customization
5nav_order: 4
6---
7
8## Function Dictionary
9
10By default, EvalEx has its own dictionary for the operators that can be used in an expression,
11the _MapBasedOperatorDictionary_. It stores and retrieves the operators in a case-insensitive
12_TreeMap_.
13
14You can easily define your own operator directory, by defining a class that implements the
15_FunctionDictionaryIfc_:
16
17```java
18public interface OperatorDictionaryIfc {
19
20 /**
21 * Allows to add an operator to the dictionary. Implementation is optional, if you have a fixed
22 * set of operators, this method can throw an exception.
23 *
24 * @param operatorString The operator name.
25 * @param operator The operator implementation.
26 */
27 void addOperator(String operatorString, OperatorIfc operator);
28
29 /**
30 * Check if the dictionary has a prefix operator with that name.
31 *
32 * @param operatorString The operator name to look for.
33 * @return <code>true</code> if an operator was found or <code>false</code> if not.
34 */
35 default boolean hasPrefixOperator(String operatorString) {
36 return getPrefixOperator(operatorString) != null;
37 }
38
39 /**
40 * Check if the dictionary has a postfix operator with that name.
41 *
42 * @param operatorString The operator name to look for.
43 * @return <code>true</code> if an operator was found or <code>false</code> if not.
44 */
45 default boolean hasPostfixOperator(String operatorString) {
46 return getPostfixOperator(operatorString) != null;
47 }
48
49 /**
50 * Check if the dictionary has an infix operator with that name.
51 *
52 * @param operatorString The operator name to look for.
53 * @return <code>true</code> if an operator was found or <code>false</code> if not.
54 */
55 default boolean hasInfixOperator(String operatorString) {
56 return getInfixOperator(operatorString) != null;
57 }
58
59 /**
60 * Get the operator definition for a prefix operator name.
61 *
62 * @param operatorString The name of the operator.
63 * @return The operator definition or <code>null</code> if no operator was found.
64 */
65 OperatorIfc getPrefixOperator(String operatorString);
66
67 /**
68 * Get the operator definition for a postfix operator name.
69 *
70 * @param operatorString The name of the operator.
71 * @return The operator definition or <code>null</code> if no operator was found.
72 */
73 OperatorIfc getPostfixOperator(String operatorString);
74
75 /**
76 * Get the operator definition for an infix operator name.
77 *
78 * @param operatorString The name of the operator.
79 * @return The operator definition or <code>null</code> if no operator was found.
80 */
81 OperatorIfc getInfixOperator(String operatorString);
82}
83```
84
85Only four methods need to be implemented:
86
87- addOperator(String operatorString, OperatorIfc operator) - which allows to add an operator.
88- OperatorIfc getPrefixOperator(String operatorString) - retrieves a prefix operator.
89- OperatorIfc getPostfixOperator(String operatorString) - retrieves a postfix operator.
90- OperatorIfc getInfixOperator(String operatorString) - retrieves a infix operator.
91
92The _addOperator()_ method is only called when an operator is added to the configuration, using the
93_withAdditionalOperators()_ in the _ExpressionConfiguration_ object.
94
95> NOTE: The operator names that are passed to the methods are case-sensitive, just like they were
96> entered in the expression.
97
98The custom operator dictionary can then be specified in the expression configuration:
99
100```java
101ExpressionConfiguration configuration = ExpressionConfiguration.builder()
102 .operatorDictionary(new MyOperatorDictionary())
103 .build();
104```