What restrictions are placed on the values of each case of a switch statement

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During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.

In Java, there are certain restrictions on the values that can be used in each case of a switch statement. Here are the key points:

  1. Must be a Constant Expression:
    • The values used in each case statement must be constant expressions. This means that they must be compile-time constants, such as literals or final variables. The compiler must be able to determine the value at compile time.
    java
    final int x = 10;
    switch (value) {
    case 1: // Valid, as 1 is a constant expression
    case x: // Valid, as x is a final variable
    // Other cases...
    }

    However, the following is not allowed:

    java
    int y = 20;
    switch (value) {
    case y: // Error, y is not a constant expression
    // Other cases...
    }
  2. No Duplicate Case Values:
    • The values specified in different case statements must be unique within the switch block. Duplicate case values are not allowed.
    java
    switch (value) {
    case 1: // Valid
    case 2: // Valid
    case 1: // Error, duplicate case value
    // Other cases...
    }
  3. Case Values Must Match the Switch Expression Type:
    • The type of values in each case statement must match the type of the switch expression.
    java
    int value = 1;
    switch (value) {
    case 1: // Valid, both are of type int
    case 'A': // Error, char cannot be compared with int without an explicit cast
    // Other cases...
    }

These restrictions are in place to ensure the reliability and predictability of switch statements in Java.