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

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.

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 92.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 92.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 43.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

PositionLiteralsFirstInCaseInsensitiveComparisons

Since: PMD 5.1

Priority: Medium

Categories: Style

Remediation Points: 50000

Position literals first in comparisons, if the second argument is null then NullPointerExceptions can be avoided, they will just return false.

Example:

class Foo {
 boolean bar(String x) {
 return x.equalsIgnoreCase('2'); // should be '2'.equalsIgnoreCase(x)
 }
}

ConfusingTernary

Since: PMD 1.9

Priority: Medium

Categories: Style

Remediation Points: 50000

Avoid negation within an 'if' expression with an 'else' clause. For example, rephrase: if (x != y) diff(); else same(); as: if (x == y) same(); else diff();. Most 'if (x != y)' cases without an 'else' are often return cases, so consistent use of this rule makes the code easier to read. Also, this resolves trivial ordering problems, such as 'does the error case go first?' or 'does the common case go first?'.

Example:

boolean bar(int x, int y) {
 return (x != y) ? diff : same;
}

PositionLiteralsFirstInCaseInsensitiveComparisons

Since: PMD 5.1

Priority: Medium

Categories: Style

Remediation Points: 50000

Position literals first in comparisons, if the second argument is null then NullPointerExceptions can be avoided, they will just return false.

Example:

class Foo {
 boolean bar(String x) {
 return x.equalsIgnoreCase('2'); // should be '2'.equalsIgnoreCase(x)
 }
}

PositionLiteralsFirstInCaseInsensitiveComparisons

Since: PMD 5.1

Priority: Medium

Categories: Style

Remediation Points: 50000

Position literals first in comparisons, if the second argument is null then NullPointerExceptions can be avoided, they will just return false.

Example:

class Foo {
 boolean bar(String x) {
 return x.equalsIgnoreCase('2'); // should be '2'.equalsIgnoreCase(x)
 }
}

PositionLiteralsFirstInCaseInsensitiveComparisons

Since: PMD 5.1

Priority: Medium

Categories: Style

Remediation Points: 50000

Position literals first in comparisons, if the second argument is null then NullPointerExceptions can be avoided, they will just return false.

Example:

class Foo {
 boolean bar(String x) {
 return x.equalsIgnoreCase('2'); // should be '2'.equalsIgnoreCase(x)
 }
}

UseUtilityClass

Since: PMD 0.3

Priority: Medium

Categories: Style

Remediation Points: 50000

For classes that only have static methods, consider making them utility classes. Note that this doesn't apply to abstract classes, since their subclasses may well include non-static methods. Also, if you want this class to be a utility class, remember to add a private constructor to prevent instantiation. (Note, that this use was known before PMD 5.1.0 as UseSingleton).

Example:

public class MaybeAUtility {
 public static void foo() {}
 public static void bar() {}
}