[java] UnnecessaryBoxing, but explicit conversion is necessary

[andygoossens]

Affects PMD Version: 7.0.0

Rule: UnnecessaryBoxing

Description: PMD reports "Unnecessary explicit conversion from Integer to Long" violation, but removing the explicit conversion will break compilation.

Code Sample demonstrating the issue:

@SuppressWarnings({"PMD.SystemPrintln", "PMD.NoPackage"})
public final class UnnecessaryBoxing {

  private UnnecessaryBoxing() {
  }

  public static void addLong(Long parameter) {
    System.out.println("parameter = " + parameter);
  }

  public static Integer getValue() {
    return 42;
  }

  public static void main(String[] args) {
    addLong(Long.valueOf(getValue())); // PMD complains: "Unnecessary explicit conversion from Integer to Long"
    //addLong(getValue()); // Does not compile: "incompatible types: Integer cannot be converted to Long"
  }
}

Expected outcome:

PMD reports a violation at line 16 (see comment), but that's wrong. That's a false positive.

Running PMD through: Gradle

[oowekyala]

That's because your code is doing the conversion chain Integer ~> int ~> long -> Long, where the first two are implicit. You can "simplify" that by writing getValue().longValue() and not call Long.valueOf. That way you do Integer -> long ~> Long. I haven't tested that this satisfies the rule but I believe it would.

Although the rule is still definitely wrong because the conversion is not unnecessary in this case.

[andygoossens]

I see. Using addLong(getValue().longValue()); in my example would indeed have satisfied the rule.