红帽全球峰会此内容没有您所选择的语言版本。
13.6. Java Expressions
| Capability | Example |
|---|---|
|
You can use any Java expression that returns a
boolean as a constraint inside the parentheses of a pattern. Java expressions can be mixed with other expression enhancements, such as property access.
|
Person( age == 50 ) |
|
You can change the evaluation priority by using parentheses, as in any logic or mathematical expression.
|
Person( age > 100 && ( age % 10 == 0 ) ) |
|
You can reuse Java methods.
|
Person( Math.round( weight / ( height * height ) ) < 25.0 ) |
|
Type coercion is always attempted if the field and the value are of different types; exceptions will be thrown if a bad coercion is attempted.
|
Person( age == "10" ) // "10" is coerced to 10 |
Warning
Methods must not change the state of the object in a way that may affect the rules. Any method executed on a fact in the LHS should be a read only method.
Warning
The state of a fact should not change between rule invocations (unless those facts are marked as updated to the working memory on every change):
Person( System.currentTimeMillis() % 1000 == 0 ) // Do NOT do this
Person( System.currentTimeMillis() % 1000 == 0 ) // Do NOT do thisImportant
All operators have normal Java semantics except for
== and !=.
The
== operator has null-safe equals() semantics:
// Similar to: java.util.Objects.equals(person.getFirstName(), "John") // so (because "John" is not null) similar to: // "John".equals(person.getFirstName()) Person( firstName == "John" )
// Similar to: java.util.Objects.equals(person.getFirstName(), "John")
// so (because "John" is not null) similar to:
// "John".equals(person.getFirstName())
Person( firstName == "John" )
The
!= operator has null-safe !equals() semantics:
// Similar to: !java.util.Objects.equals(person.getFirstName(), "John") Person( firstName != "John" )
// Similar to: !java.util.Objects.equals(person.getFirstName(), "John")
Person( firstName != "John" )
'%20d='M201.5%20305.5c-13.8%200-24.9-11.1-24.9-24.6%200-13.8%2011.1-24.9%2024.9-24.9%2013.6%200%2024.6%2011.1%2024.6%2024.9%200%2013.6-11.1%2024.6-24.6%2024.6zM504%20256c0%20137-111%20248-248%20248S8%20393%208%20256%20119%208%20256%208s248%20111%20248%20248zm-132.3-41.2c-9.4%200-17.7%203.9-23.8%2010-22.4-15.5-52.6-25.5-86.1-26.6l17.4-78.3%2055.4%2012.5c0%2013.6%2011.1%2024.6%2024.6%2024.6%2013.8%200%2024.9-11.3%2024.9-24.9s-11.1-24.9-24.9-24.9c-9.7%200-18%205.8-22.1%2013.8l-61.2-13.6c-3-.8-6.1%201.4-6.9%204.4l-19.1%2086.4c-33.2%201.4-63.1%2011.3-85.5%2026.8-6.1-6.4-14.7-10.2-24.1-10.2-34.9%200-46.3%2046.9-14.4%2062.8-1.1%205-1.7%2010.2-1.7%2015.5%200%2052.6%2059.2%2095.2%20132%2095.2%2073.1%200%20132.3-42.6%20132.3-95.2%200-5.3-.6-10.8-1.9-15.8%2031.3-16%2019.8-62.5-14.9-62.5zM302.8%20331c-18.2%2018.2-76.1%2017.9-93.6%200-2.2-2.2-6.1-2.2-8.3%200-2.5%202.5-2.5%206.4%200%208.6%2022.8%2022.8%2087.3%2022.8%20110.2%200%202.5-2.2%202.5-6.1%200-8.6-2.2-2.2-6.1-2.2-8.3%200zm7.7-75c-13.6%200-24.6%2011.1-24.6%2024.9%200%2013.6%2011.1%2024.6%2024.6%2024.6%2013.8%200%2024.9-11.1%2024.9-24.6%200-13.8-11-24.9-24.9-24.9z'/%3e%3c/svg%3e){kind=small}