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

Cognitive Complexity is a measure of how hard the control flow of a method is to understand. Methods with high Cognitive Complexity will be difficult to maintain.

See

• Cognitive Complexity

Passing message arguments that require further evaluation into a Guava com.google.common.base.Preconditions check can result in a performance penalty. That's because whether or not they're needed, each argument must be resolved before the method is actually called.

Similarly, passing concatenated strings into a logging method can also incur a needless performance hit because the concatenation will be performed every time the method is called, whether or not the log level is low enough to show the message.

Instead, you should structure your code to pass static or pre-computed values into Preconditions conditions check and logging calls.

Specifically, the built-in string formatting should be used instead of string concatenation, and if the message is the result of a method call, then Preconditions should be skipped altogether, and the relevant exception should be conditionally thrown instead.

Noncompliant Code Example

logger.log(Level.DEBUG, "Something went wrong: " + message);  // Noncompliant; string concatenation performed even when log level too high to show DEBUG messages

logger.fine("An exception occurred with message: " + message); // Noncompliant

LOG.error("Unable to open file " + csvPath, e);  // Noncompliant

Preconditions.checkState(a > 0, "Arg must be positive, but got " + a);  // Noncompliant. String concatenation performed even when a > 0

Preconditions.checkState(condition, formatMessage());  // Noncompliant. formatMessage() invoked regardless of condition

Preconditions.checkState(condition, "message: %s", formatMessage());  // Noncompliant

Compliant Solution

logger.log(Level.SEVERE, "Something went wrong: {0} ", message);  // String formatting only applied if needed

logger.fine("An exception occurred with message: {}", message);  // SLF4J, Log4j

logger.log(Level.SEVERE, () -> "Something went wrong: " + message); // since Java 8, we can use Supplier , which will be evaluated lazily

LOG.error("Unable to open file {0}", csvPath, e);

if (LOG.isDebugEnabled() {
  LOG.debug("Unable to open file " + csvPath, e);  // this is compliant, because it will not evaluate if log level is above debug.
}

Preconditions.checkState(arg > 0, "Arg must be positive, but got %d", a);  // String formatting only applied if needed

if (!condition) {
  throw new IllegalStateException(formatMessage());  // formatMessage() only invoked conditionally
}

if (!condition) {
  throw new IllegalStateException("message: " + formatMessage());
}

Exceptions

catch blocks are ignored, because the performance penalty is unimportant on exceptional paths (catch block should not be a part of standard program flow). Getters are ignored as well as methods called on annotations which can be considered as getters. This rule accounts for explicit test-level testing with SLF4J methods isXXXEnabled and ignores the bodies of such if statements.

Duplicated string literals make the process of refactoring error-prone, since you must be sure to update all occurrences.

On the other hand, constants can be referenced from many places, but only need to be updated in a single place.

Noncompliant Code Example

With the default threshold of 3:

public void run() {
  prepare("action1");                              // Noncompliant - "action1" is duplicated 3 times
  execute("action1");
  release("action1");
}

@SuppressWarning("all")                            // Compliant - annotations are excluded
private void method1() { /* ... */ }
@SuppressWarning("all")
private void method2() { /* ... */ }

public String method3(String a) {
  System.out.println("'" + a + "'");               // Compliant - literal "'" has less than 5 characters and is excluded
  return "";                                       // Compliant - literal "" has less than 5 characters and is excluded
}

Compliant Solution

private static final String ACTION_1 = "action1";  // Compliant

public void run() {
  prepare(ACTION_1);                               // Compliant
  execute(ACTION_1);
  release(ACTION_1);
}

Exceptions

To prevent generating some false-positives, literals having less than 5 characters are excluded.

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks that the groups of import declarations appear in the order specifiedby the user. If there is an import but its group is not specified in theconfiguration such an import should be placed at the end of the import list.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks that the groups of import declarations appear in the order specifiedby the user. If there is an import but its group is not specified in theconfiguration such an import should be placed at the end of the import list.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks that the groups of import declarations appear in the order specifiedby the user. If there is an import but its group is not specified in theconfiguration such an import should be placed at the end of the import list.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks the placement of right curly braces ('}') for code blocks.This check supports if-else, try-catch-finally blocks, while-loops, for-loops,method definitions, class definitions, constructor definitions,instance, static initialization blocks, annotation definitions and enum definitions.For right curly brace of expression blocks of arrays, lambdas and class instancesplease follow issue#5945.For right curly brace of enum constant please follow issue#7519.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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

Checks for long lines.

Rationale: Long lines are hard to read in printouts or if developershave limited screen space for the source code, e.g. if the IDEdisplays additional information like project tree, class hierarchy,etc.

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