Switch Statement Should Have Default Branch

ID

java.switch_on_enum_full_coverage

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

CWE:478, code-style, reliability

Description

Reports classic switch statements that do not contain a default branch. A missing default means that new values (especially when the switched expression is an enum) silently fall through without executing any code, causing hard-to-find bugs when the type grows.

Rationale

When a switch lacks a default branch and a value is encountered that does not match any case, execution silently skips the entire switch body. This is particularly dangerous with enums: adding a new constant to an enum will compile cleanly but produce incorrect behavior at every switch site that does not handle it.

// Bad: no default branch
switch (color) {
    case RED:
        paint(RED);
        break;
    case GREEN:
        paint(GREEN);
        break;
    // BLUE silently ignored if added later
}

Remediation

Always include a default branch, even if only to throw an exception or log an unexpected value:

// Good: explicit default
switch (color) {
    case RED:
        paint(RED);
        break;
    case GREEN:
        paint(GREEN);
        break;
    default:
        throw new IllegalArgumentException("Unexpected color: " + color);
}

References