Java Switch Enhancements by JDK Version

🧱 JDK 1.0 — Classic switch (primitive types only)

Works with: int, byte, short, char

int day = 2;
String result;

switch (day) {
    case 1:
        result = "Monday";
        break;
    case 2:
        result = "Tuesday";
        break;
    default:
        result = "Invalid";
}

System.out.println(result);

✅ Output:

Tuesday

🧠 Notes: Needs break to prevent fall-through.

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🧩 JDK 5 — Enum Support in switch

enum Day { MONDAY, TUESDAY, WEDNESDAY }

Day today = Day.TUESDAY;

switch (today) {
    case MONDAY:
        System.out.println("Start of week");
        break;
    case TUESDAY:
        System.out.println("Second day");
        break;
    default:
        System.out.println("Midweek or later");
}

✅ Output:

Second day

🧠 Notes: Enum constants (MONDAY, TUESDAY, etc.) can be used as case labels.

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🔤 JDK 7 — String Support in switch

String command = "start";

switch (command) {
    case "start":
        System.out.println("Application starting...");
        break;
    case "stop":
        System.out.println("Application stopping...");
        break;
    default:
        System.out.println("Unknown command");
}

✅ Output:

Application starting...

🧠 Notes: Behind the scenes, Java uses String.hashCode() and equals checks.

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⚙️ JDK 14 — Switch Expressions with yield (Standard)

int day = 6;

String type = switch (day) {
    case 1, 2, 3, 4, 5 -> "Weekday";
    case 6, 7 -> {
        System.out.println("Weekend logic here");
        yield "Weekend"; // return value from block
    }
    default -> "Invalid";
};

System.out.println(type);

✅ Output:

Weekend logic here
Weekend

🧠 Notes:

• switch can now return values.
• yield used for block-style cases.

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🧠 JDK 21 — Pattern Matching for switch (Standard)

static String describe(Object obj) {
    return switch (obj) {
        case String s -> "Short string";
        case Integer i -> "Integer: " + i;
        case null -> "Null value";
        default -> "Unknown type";
    };
}

public static void main(String[] args) {
    System.out.println(describe("Hello"));
    System.out.println(describe("Welcome"));
    System.out.println(describe(42));
    System.out.println(describe(null));
}

✅ Output:

Short string
Long string
Integer: 42
Null value

🧠 Notes:

• switch now supports type matching, guarded patterns, and null-safe handling.
• Fully standardized in JDK 21 (no preview flags needed).

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✅ Summary Overview

JDK	Feature	Example Concept	Highlight
1.0	Classic switch	Works on int, needs break	Basic control flow
5	Enum support	case MONDAY:	Type-safe enum usage
7	String support	case "start":	String-based branching
14	Switch expressions + yield	yield "Weekend";	Expression switch, returns value
21	Pattern matching	case String s && s.length()>5 -> ...	Type-safe, null-safe, concise

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