j21-switch - Blog of Vincent VAUBAN

🧠 Switch Expressions in Java— Illustrated with French Poets Across Centuries

Like all expressions, switch expressions in Java evaluate to a single value. This value can be used directly in assignments or output statements.Starting with Java 14, we can use the more concise and safer case L -> labels. These eliminate the need for break statements and make the code easier to read and less error-prone. When needed, you can also use yield in a block to return a value.📖 For the design motivation behind this feature, see JEP 361.

🎨 Example Scenario — Poets and Their CenturiesLet’s say you’re working with an enum of famous French poets, and you want to determine the century in which each poet lived and wrote.

public enum Poet {
    DU_BELLAY, RONSARD,           // 16th century
    LA_FONTAINE, MALHERBE,        // 17th century
    VOLTAIRE, CHENIER,            // 18th century
    HUGO, BAUDELAIRE,             // 19th century
    ARAGON, ELUARD,               // 20th century
    GLISSANT, CONFIANT            // 21st century
}

🐢 Classic Switch StatementHere's how this might look using a traditional switch statement to determine a poet’s century:

int century = 0;
Poet poet = Poet.BAUDELAIRE;

switch (poet) {
    case DU_BELLAY, RONSARD:
        century = 16;
        break;
    case LA_FONTAINE, MALHERBE:
        century = 17;
        break;
    case VOLTAIRE, CHENIER:
        century = 18;
        break;
    case HUGO, BAUDELAIRE:
        century = 19;
        break;
    case ARAGON, ELUARD:
        century = 20;
        break;
    case GLISSANT, CONFIANT:
        century = 21;
        break;
    default:
        throw new IllegalStateException("Unknown poet: " + poet);
}

System.out.println("Century: " + century + "th");

👎 Downsides of the classic approach:🟣 You have to declare and mutate a variable (century).🟣 You must remember to add break statements — forgetting one could cause fall-through bugs.

⚡ Modern Switch ExpressionWith switch expressions, this becomes much cleaner and less error-prone:

Poet poet = Poet.BAUDELAIRE;

System.out.println(
    switch (poet) {
        case DU_BELLAY, RONSARD        -> 16;
        case LA_FONTAINE, MALHERBE     -> 17;
        case VOLTAIRE, CHENIER         -> 18;
        case HUGO, BAUDELAIRE          -> 19;
        case ARAGON, ELUARD            -> 20;
        case GLISSANT, CONFIANT        -> 21;
        default -> throw new IllegalStateException("Unknown poet: " + poet);
    }
);

🧾 Why It’s Better🟣 Each case is followed by ->, which directly points to a returned value.🟣 No need for break.🟣 The whole construct is an expression, which means you can assign or return it inline.🟣 It's safe by design — no fall-through means fewer bugs.

📌 Summary✅ case L -> is called a switch labeled rule.🟣 Avoids the need for break.🟣 Prevents accidental fall-through.🟣 Can be used in both expressions and statements.🟣 Makes your code cleaner, safer, and more expressive.