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All currently implemented checks

General Checks

  • For-loop should be for each loop
  • @Override missing
  • Field should be a local variable (a bit flaky rn, may produce false positives)
  • Constants should be static final and have a UPPER_SNAKE_CASE name
  • Double-brace initialization used
  • Equals does not check for null values
  • Objects should be compared with equals and not via toString
  • Method parameters shouldn't be reassigned
  • Attribute should be a local variable
  • System-dependent linebreak used in string literal
  • Labels should be avoided
  • Fields should not be hidden by variables
  • Scanners should be closed
  • Unchecked type casts should be avoided

Java API

  • isEmpty should be used on Strings/Collections instead of comparing the length/size against 0
  • Old/Deprecated collections such as Stack shouldn't be used
  • use String.formatted over String.format
  • Tri-state optionals should be avoided
  • Optional as arguments

Unnecessary Complexity

  • Class explicitly extends Object
  • Diamond Operator should be used
  • Redundant modifiers
  • Redundant returns
  • Unnecessary local creation before returns (int x = 0; return x;)
  • Unused imports (sometimes also reports star imports)
  • Instantiation of primitive wrappers
  • Redundant default constructor (this check may report default constructors with custom JavaDoc)
  • For loop should have exactly one loop variable
  • Empty non-catch block
  • All locals, parameters, private fields & private methods should be used
  • Unnecessary if as the value of the condition should be directly used (e.g. if (x) { return true; } else { false; })
  • Variable is reassigned to itself
  • Overwriting default values in arrays with default values
  • Not using operator assignments (e.g. x = x + 1 instead of x += 1)

Debugging Artifacts

  • Assertions used
  • Exception#printStackTrace used

Exceptions

  • Empty catch block
  • Runtime exception or error is caught
  • Custom exception inherits from RuntimeException or Error
  • Exception is thrown and immediately caught in the same method

Comments & JavaDoc

  • Method returns null in some tests but the Javadoc doesn't mention it
  • Not all comments are either in German or in English (ignores very short comments)
  • JavaDoc contains tags with empty descriptions
  • Commented out code should be removed
  • The @author tag should match a specified Regex
  • JavaDoc for methods should mention all parameters

Naming

  • Getters for Booleans should be named isXYZ
  • Method names should follow linguistic conventions (see the PMD documentation)
  • Variables should not have overly short names or be abbreviations of their types
  • Constants should have descriptive names (i.e. not PARAM_ONE for 1)

OOP

  • Methods should never return concrete collection types but e.g. List or Set. The same applies to fields.
  • Methods in abstract classes should be abstract instead of providing a dummy implementation
  • Mutable lists in fields should be copied before returning them
  • Utility classes should have only final fields and a single private no-arg constructor
  • Interfaces should not have fields, constants or be empty
  • Input/Output should be separated from the program logic
  • System.exit() should never be used
  • Innere Klassen sollten in einer eigenen Datei liegen

Code Structure

  • The default package should not be used