Description

Pattern variables are not implicitly final in Java, and they can be reassigned. This check verifies that pattern variables are explicitly declared as final if they are not reassigned within their flow scope.

Examples

To configure the check:

<module name="Checker">
  <module name="TreeWalker">
    <module name="FinalPatternVariable"/>
  </module>
</module>

Example of violations:

class Example1 {
  void method(Object obj) {
    // violation below 'Pattern variable 'str' should be declared final.'
    if (obj instanceof String str) {
      System.out.println(str);
    }

    if (obj instanceof final String str) {
      System.out.println(str);
    }

    if (obj instanceof String str) {
      str = "new value";
      System.out.println(str);
    }
  }
}

Example of Usage

• Checkstyle Style

Violation Messages

• final.pattern.variable

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Fully Qualified Name

com.puppycrawl.tools.checkstyle.checks.coding.FinalPatternVariableCheck

Use this fully qualified class name in configuration when an exact class reference is required.

Parent Module

TreeWalker