$ cat Test.java 
public class Test {
enum Color { RED, GREEN, BLUE, MY_COLOR }

/**
 * In the case of switch expressions, the compiler requires
 * that they are exhaustive, so this check does not enforce
 * a default label. This code would still compile with a
 * default label, but it is unnecessary so this check does
 * not enforce it.
 */
static int showSwitchExpressionExhaustiveness(Color color) {
    switch (color) {
        case RED: System.out.println("RED"); break;
        case BLUE: System.out.println("BLUE"); break;
        case GREEN: System.out.println("GREEN"); break;
        // Check will require default label below, compiler
        // does not enforce a switch statement with constants
        // to be complete.
        //default: System.out.println("Something else");
    }

    // Check will not require default label in switch
    // expression below, because code will not compile
    // if all possible values are not handled. If the
    // 'Color' enum is extended, code will fail to compile.
    return switch (color) {
        case RED:
            yield 1;
        case GREEN:
            yield 2;
        case BLUE:
            yield 3;
    };
}

  }

$ javac --enable-preview --release 17 Test.java 
Test.java:26: error: the switch expression does not cover all possible input values
    return switch (color) {
           ^
1 error