encryptorcode/iam-oauth

Utility classes, which are collections of static members, are not meant to be instantiated. Even abstract utility classes, which can be extended, should not have public constructors.

Java adds an implicit public constructor to every class which does not define at least one explicitly. Hence, at least one non-public constructor should be defined.

Noncompliant Code Example

class StringUtils { // Noncompliant

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

Compliant Solution

class StringUtils { // Compliant

  private StringUtils() {
    throw new IllegalStateException("Utility class");
  }

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

Exceptions

When class contains public static void main(String[] args) method it is not considered as utility class and will be ignored by this rule.

When java.io.File#delete fails, this boolean method simply returns false with no indication of the cause. On the other hand, when java.nio.file.Files#delete fails, this void method returns one of a series of exception types to better indicate the cause of the failure. And since more information is generally better in a debugging situation, java.nio.file.Files#delete is the preferred option.

Noncompliant Code Example

public void cleanUp(Path path) {
  File file = new File(path);
  if (!file.delete()) {  // Noncompliant
    //...
  }
}

Compliant Solution

public void cleanUp(Path path) throws NoSuchFileException, DirectoryNotEmptyException, IOException {
  Files.delete(path);
}

Checks that there are no import statements that use the * notation.

Rationale: Importing all classes from a package or staticmembers from a class leads to tight coupling between packagesor classes and might lead to problems when a new version of alibrary introduces name clashes.

This documentation is written and maintained by the Checkstyle community and is covered under the same license as the Checkstyle project.