Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Deprecation should be marked with both the @Deprecated annotation and @deprecated Javadoc tag. The annotation enables tools such as IDEs to warn about referencing deprecated elements, and the tag can be used to explain when it was deprecated, why, and how references should be refactored.

Further, Java 9 adds two additional arguments to the annotation:

• since allows you to describe when the deprecation took place
• forRemoval, indicates whether the deprecated element will be removed at some future date

If your compile level is Java 9 or higher, you should be using one or both of these arguments.

Noncompliant Code Example

class MyClass {

  @Deprecated
  public void foo1() {
  }

  /**
    * @deprecated
    */
  public void foo2() {    // Noncompliant
  }

}

Compliant Solution

class MyClass {

  /**
    * @deprecated (when, why, refactoring advice...)
    */
  @Deprecated
  public void foo1() {
  }

  /**
    * Java >= 9
    * @deprecated (when, why, refactoring advice...)
    */
  @Deprecated(since="5.1")
  public void foo2() {
  }

  /**
    * Java >= 9
    * @deprecated (when, why, refactoring advice...)
    */
  @Deprecated(since="4.2", forRemoval=true)
  public void foo3() {
  }

}

Exceptions

The members and methods of a deprecated class or interface are ignored by this rule. The classes and interfaces themselves are still subject to it.

/**
 * @deprecated (when, why, etc...)
 */
@Deprecated
class Qix  {

  public void foo() {} // Compliant; class is deprecated

}

/**
 * @deprecated (when, why, etc...)
 */
@Deprecated
interface Plop {

  void bar();

}

Abstract classes should not have public constructors. Constructors of abstract classes can only be called in constructors of their subclasses. So there is no point in making them public. The protected modifier should be enough.

Noncompliant Code Example

public abstract class AbstractClass1 {
    public AbstractClass1 () { // Noncompliant, has public modifier
        // do something here
    }
}

Compliant Solution

public abstract class AbstractClass2 {
    protected AbstractClass2 () {
        // do something here
    }
}