Issue
I recently discovered, that in a java switch statement, multiple labels can be chained, but for no apparent effect. And it even allows labels that do not exist. For example you can do this:
case ENUM_VALUE_1:ENUM_VALUE_2:
, or even this case ENUM_VALUE_1:foobar:barfoo:
. As long as it ends with a colon, any value seems to be accepted.
First I though this might be a different way of grouping multiple cases, but that does not seem to be working. So I ran the following test
public class Main {
public enum TestEnum {
A,
B
}
public static void main(String[] args) {
TestEnum testEnum = TestEnum.B;
switch (testEnum) {
case A: System.out.println("Test 1: Case 1"); break;
case B: System.out.println("Test 1: Case 2"); break;
}
switch (testEnum) {
case A: System.out.println("Test 2: Case 1"); break;
case B:A: System.out.println("Test 2: Case 2"); break; // Label A is already used in enum
}
switch (testEnum) {
case A:B: System.out.println("Test 3: Case 1"); break; // Label B is already used in enum
case B: System.out.println("Test 3: Case 2"); break;
}
switch (testEnum) {
case A:BARFOO: System.out.println("Test 4: Case 1"); break; // Label BARFOO does not exist
case B:FOOBAR: System.out.println("Test 4: Case 2"); break; // Label FOOBAR does not exist
}
switch (testEnum) {
case A:B: System.out.println("Test 5: Case 1"); break;
}
}}
I ran it in java 11 and 17 and the output in both versions is:
Test 1: Case 2
Test 2: Case 2
Test 3: Case 2
Test 4: Case 2
I would have expected that only test 1 and 5 actually compile, but they all compile and it seems that everything after the actual label is just ignored.
I doubt this is an oversight, so what am I missing?
Solution
Where in your code you have something like this:
case A:BARFOO:
BARFOO:
isn't a switch case. It's nothing to do with the switch mechanics. It's just a label. You're allowed to label any statement, but it's not always useful. It's typically used for loops: e.g.
outerloop:
while (true) {
while (true) {
break outerloop;
}
}
If you actually wanted to group together multiple cases, you could write it like:
case A: case B:
...
break;
And as Jesper mentions in the comments, more recent versions of Java also support a switch expression, under which the syntax is:
case A, B -> ...
Answered By - khelwood Answer Checked By - Cary Denson (PHPFixing Admin)
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