为什么JUnit中的@Rule注释字段必须是公共的？

Question

In JUnit test case, a field annotated by @Rule must be public. It breaks a common Java coding convention (all class member variables should not be public). Why does JUnit require this?

Documentation for @Rule : https://github.com/junit-team/junit/blob/master/src/main/java/org/junit/Rule.java

Answer 1

The JUnit runner will need to access the field reflectively to run the rule. If the field was private the access would throw IllegalAccessException .

Another option would have been to have the runner modify the access from private to public before running the rule. However that could cause problems in case a security manager is enabled.

If you want to avoid having public fields in your test class you can from JUnit 4.11 annotate methods that return a Rule with @Rule or @ClassRule .