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"switch" Statements Should Have "Default" Clauses

High
reliabilitydefensive programming

What is it?​

This practice is triggered by the absence of a default clause in a switch statement, which can lead to missed cases and unexpected behavior.

Why apply it?​

Having a default clause ensures that even when cases do not match any specified criteria, the program takes a controlled, defined action. This prevents potential logical errors and ensures code robustness.

How to fix it?​

Add a default clause at the end of your switch statements to define a clear action or to document why no action is needed when no other case is matched.

Examples​

Example 1:​

Negative​

This negative example lacks a default case, leaving some actions unhandled.

public class ActionHandler {
    public void handleAction(String action) {
        switch (action) {
          case "START":
            System.out.println("Starting");
            break;
          case "STOP":
            System.out.println("Stopping");
            break;
          // No default case to handle other actions
        }
    }
}

Example 2:​

Negative​

This negative example misses a default clause, which can lead to ignored values if they don't match any case.

switch (param) {
  case 0:
    System.out.println("Zero");
    break;
  case 1:
    System.out.println("One");
    break;
  // Missing default clause
}

Example 3:​

Positive​

This positive example shows a switch statement with a proper default clause handling unexpected values.

switch (param) {
  case 0:
    System.out.println("Zero");
    break;
  case 1:
    System.out.println("One");
    break;
  default:
    System.out.println("Unexpected value");
    break;
}

Negative​

This negative example ignores the need for a default case, missing error handling for invalid operations.

public int calculate(int a, int b, String operation) {
    switch (operation) {
      case "ADD":
        return a + b;
      case "SUBTRACT":
        return a - b;
      // Missing default causes lack of handling for unsupported operations
    }
}

Example 4:​

Positive​

This positive example demonstrates a switch statement with a default clause to handle unrecognized actions.

public class ActionHandler {
    public void handleAction(String action) {
        switch (action) {
          case "START":
            System.out.println("Starting");
            break;
          case "STOP":
            System.out.println("Stopping");
            break;
          default:
            System.out.println("Unknown action");
            break;
        }
    }
}

Example 5:​

Positive​

This positive example uses a switch with a proper default clause in a calculation context.

public int calculate(int a, int b, String operation) {
    switch (operation) {
      case "ADD":
        return a + b;
      case "SUBTRACT":
        return a - b;
      default:
        throw new IllegalArgumentException("Invalid operation");
    }
}