Java switch statement: Constant expression required, but it IS constant

java

constant-expression

switch-statement

java-best-practices

byAnton Shumikhin·Feb 27, 2025

In Java switch cases, ensure you use final constants or literals directly. Variables won't make the cut unless final. For parenthesis' sake:

final int SOME_MAGIC_NUMBER = 42; // Who needs a formula when you find the Ultimate Answer?
switch (lifeUniverseEverything) {
    case SOME_MAGIC_NUMBER: // Look, mom, no compile-time errors!
        // Do magic
        break;
    // You can add a few more existential cases here
}

For your switch to handle real compile-time constants, brace your static fields with:

public static final int AS_CONSTANT_AS_GRAVITY = 10; // Unless you're Einstein, then it's not so constant.

Navigating the switch maze

In the quest to conquer the switch castle, remember the rules of the realm are strict and often counter-intuitive. Here's a map to help you through.

Clad your ints in Enum armor

Enums are your non-funky, type safe companions in the world of switches, enhancing maintainability. Ride along with them:

enum Light {
    RED, GREEN, YELLOW;
}

Light trafficLight = Light.GREEN;
switch (trafficLight) {
    case RED:   // Goes without saying, no stoppage of flow here
    case GREEN: // We can go, folks. Shoutout to all environment lovers!
    case YELLOW: // The middle earth
        // Code block
        break;
    // Don't even need a default if you cover all enums. Talk about being inclusive!
}

For resilience, including a default case is advised. But what's life without a bit of thrill?

Dancing with dynamic values

Verify that all labels in switch case are immutable at runtime. Fail to do this and you summon menacing compile-time errors. They are not as fun as they sound.

The constant conundrums

Java constant expressions - those that yield a constant value that can be divined at compile time. Here's your Rosetta Stone:

Types that pass the test

Java is a stickler for primitive types and String for switch statement cases. This ensures a fair fight during compilation.

All that glitters is not constant

Labeling a variable as final doesn't automatically crown it a constant expression. It should also be initialized with a immutable expression, like a literal or an enum.

Constants - your reliable comrades

Use constant expressions when you want a value steady as a rock, shared across multiple classes or methods. They won't let you down when playing with predictable and reliable switch case labels.

Traps to avoid

The "Constant expression required" error is a landmine, often triggered when using variables that aren't final static fields initialized with constant expressions. Example:

public static int NOT_SO_CONSTANT = new Random().nextInt(10); // Well, this escalated quickly!

explain-codes / Java / Java switch statement: Constant expression required, but it IS constant

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Navigating the switch maze The constant conundrums