Why isn't unreachable code detected when if condition is a constant expression?

I'm studying for a Java exam and came across the "unreachable statement" compiler error, e.g.

Source.java:10: error: unreachable statement
       System.out.println("This code is not reachable");

Am trying to understand when this would or wouldn't happen - e.g. it doesn't happen for these cases:

// Case #1
if (true) {
    System.out.println("This code is reachable");
} else {
    System.out.println("This code is not reachable"); // Compiles OK
}

// Case #2
for (i = 0; i < 5; i++) {
    if (true) continue;
    System.out.println("This code is not reachable"); // Compiles OK
}

It seems the compiler isn't smart enough to detect when the if condition is constantly true - could someone provide a more detailed explanation?