MissingSwitchDefault

Since Checkstyle 3.1

Description

Checks that switch statement has a default clause.

Rationale: It's usually a good idea to introduce a default case in every switch statement. Even if the developer is sure that all currently possible cases are covered, this should be expressed in the default branch, e.g. by using an assertion. This way the code is protected against later changes, e.g. introduction of new types in an enumeration type.

This check does not validate any switch expressions. Rationale: The compiler requires switch expressions to be exhaustive. This means that all possible inputs must be covered.

This check does not validate switch statements that use pattern or null labels. Rationale: Switch statements that use pattern or null labels are checked by the compiler for exhaustiveness. This means that all possible inputs must be covered.

See the Java Language Specification for more information about switch statements and expressions.

See the Java Language Specification for more information about patterns.

Examples

To configure the check: 

<module name="Checker">
  <module name="TreeWalker">
    <module name="MissingSwitchDefault"/>
  </module>
</module>

Example of violation: 

class Example1 {
  void Example1(int i) {
    switch (i) { // violation, 'switch without "default" clause'
      case 1:
        break;
      case 2:
        break;
    }
  }
}

Example of correct code: 

class Example2 {
  Example2(int i){
    switch (i) {
      case 1:
        break;
      case 2:
        break;
      default:
        break;
    }
    Object obj = "example";
    switch (obj) {
      case String s: // type pattern
        System.out.println(s);
        break;
      case Integer j: // type pattern
        System.out.println("Integer");
        break;
      default:    // will not compile without default label
        System.out.println("Unknown type");
        break;
    }
  }
}

Example of correct code which does not require default labels: 

sealed interface S permits A, B, C {}
final class A implements S {}
final class B implements S {}
record C(int i) implements S {}  // Implicitly final
class Example3 {
  static void showSealedCompleteness(S s) {
    switch (s) {
      case A a:
        System.out.println("A");
        break;
      case B b:
        System.out.println("B");
        break;
      case C c:
        System.out.println("C");
        break;
    }
  }
  static void showTotality(String s) {
    switch (s) {
      case Object o: // total type pattern
        System.out.println("o!");
    }
  }
  enum Color {RED, GREEN, BLUE}
  static int showSwitchExpressionExhaustiveness(Color color) {
    switch (color) {
      case RED:
        System.out.println("RED");
        break;
      case BLUE:
        System.out.println("BLUE");
        break;
      case GREEN:
        System.out.println("GREEN");
        break;
      default:
        System.out.println("Something else");
    }
    return switch (color) {
      case RED:
        yield 1;
      case GREEN:
        yield 2;
      case BLUE:
        yield 3;
    };
  }
}

Example of Usage

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.coding

Parent Module

TreeWalker