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

When the execution is not explicitly terminated at the end of a switch case, it continues to execute the statements of the following case. While this is sometimes intentional, it often is a mistake which leads to unexpected behavior.

Noncompliant Code Example

switch (myVariable) {
  case 1:
    foo();
    break;
  case 2:  // Both 'doSomething()' and 'doSomethingElse()' will be executed. Is it on purpose ?
    doSomething();
  default:
    doSomethingElse();
    break;
}

Compliant Solution

switch (myVariable) {
  case 1:
    foo();
    break;
  case 2:
    doSomething();
    break;
  default:
    doSomethingElse();
    break;
}

Exceptions

This rule is relaxed in the following cases:

switch (myVariable) {
  case 0:                                // Empty case used to specify the same behavior for a group of cases.
  case 1:
    doSomething();
    break;
  case 2:                                // Use of return statement
    return;
  case 3:                                // Use of throw statement
    throw new IllegalStateException();
  case 4:                                // Use of continue statement
    continue;
  default:                               // For the last case, use of break statement is optional
    doSomethingElse();
}

See

• MITRE, CWE-484 - Omitted Break Statement in Switch
• CERT, MSC17-C. - Finish every set of statements associated with a case label with a break statement
• CERT, MSC52-J. - Finish every set of statements associated with a case label with a break statement

The requirement for a final default clause is defensive programming. The clause should either take appropriate action, or contain a suitable comment as to why no action is taken.

Noncompliant Code Example

switch (param) {  //missing default clause
  case 0:
    doSomething();
    break;
  case 1:
    doSomethingElse();
    break;
}

switch (param) {
  default: // default clause should be the last one
    error();
    break;
  case 0:
    doSomething();
    break;
  case 1:
    doSomethingElse();
    break;
}

Compliant Solution

switch (param) {
  case 0:
    doSomething();
    break;
  case 1:
    doSomethingElse();
    break;
  default:
    error();
    break;
}

Exceptions

If the switch parameter is an Enum and if all the constants of this enum are used in the case statements, then no default clause is expected.

Example:

public enum Day {
    SUNDAY, MONDAY
}
...
switch(day) {
  case SUNDAY:
    doSomething();
    break;
  case MONDAY:
    doSomethingElse();
    break;
}

See

• MITRE, CWE-478 - Missing Default Case in Switch Statement
• CERT, MSC01-C. - Strive for logical completeness

Checks for fall-through in switchstatements. Finds locations where a casecontains Java code but lacks a break, return,throw or continuestatement.

The check honors special comments to suppress the warning.By default the texts"fallthru", "fall thru", "fall-thru","fallthrough", "fall through", "fall-through""fallsthrough", "falls through", "falls-through" (case sensitive).The comment containing these words must be all on one line,and must be on the last non-empty line before thecase triggering the warning or onthe same line before the case(ugly, but possible).

Note: The check assumes that there is no unreachablecode in the case.

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