Missing Switch Default

ID

java.missing_switch_default

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

reliability

Description

Reports classic switch statements that do not declare a default clause. Switch expressions (Java 14+) are exempt because the compiler already enforces exhaustiveness.

Rationale

A switch without default silently does nothing when the selector takes an unexpected value. Over time the set of possible values tends to grow — a new enum constant, a new status code, a new wire-level opcode — and every missing default becomes a place where behaviour is implicitly "ignore".

Explicit default has two benefits:

  • It forces the author to decide what happens for unknown values (log, throw, fall-back…).

  • It makes the intent visible to readers: "yes, we thought about it; the correct behaviour is X".

// Bad — silently no-ops for any value other than 1 or 2
switch (code) {
    case 1: handleOne(); break;
    case 2: handleTwo(); break;
}

Remediation

Add an explicit default. For switches over enum values where every constant is already handled, default typically throws to guard against future additions:

// Good — explicit default
switch (code) {
    case 1: handleOne(); break;
    case 2: handleTwo(); break;
    default:
        throw new IllegalArgumentException("unknown code: " + code);
}

Prefer switch expressions when possible — they require exhaustiveness and eliminate this concern at the language level:

return switch (code) {
    case 1 -> handleOne();
    case 2 -> handleTwo();
    default -> throw new IllegalArgumentException("unknown code: " + code);
};

References