switch expression can't be float, double or boolean

Question

Why doesn't the switch expression allow long, float, double or boolean values in Java? why is only int (and those that are automatoically promoted to int) allowed?

Denisdenise

switch exists for boolean, it is called if ... else – Hertel

Due to the precision problem , i think they are not allowed. – Vaginitis

@Denisdenise I didn't like any of the answer here: have you seen this post: Question about switch{} case in C? – Friendly

Closely related to, but not quite a duplicate of #2676710 – Trencher

Answer 1

Float and double would be awkward to use reliably even if they were possible - don't forget that performing exact equality matches on float/double is usually a bad idea anyway, due to the nature of the representation.

For Boolean values, why not just use if to start with?

I can't remember ever wanting to switch on any of these types, to be honest. Do you have a particular use case in mind?

Upstairs

I could see a use case for float or double for version information. 1.1 will always be 1.1 if you don't do any calculations. Even Java uses this trick to display version information sometimes. But I guess we'll have to byte the bullit and compare against an actual object instance representing a Version - or use String comparison from Java 7 onwards of course. – Almsgiver

@owlstead: 1.1 isn't a valid float or double number. You can have a literal which will convert to the closest float or double, but neither can precisely-represent 1.1. Did you actually mean version 1.100000000000000088817841970012523233890533447265625 (double) or version 1.10000002384185791015625 (float)? – Upstairs

Would that matter? I presume that if you parse a String then you will get either of the numbers. But I can see where it could go wrong if you mix floats and doubles. So probably the Java devs where right to leave it out. Anyway, since 1.7 there is the String switch which does not have these issues. Using a double or float for a version is a hack anyway. – Almsgiver

@owlstead: It matters because it's fundamentally an inappropriate type to use. Also, what do you do for more specific versions? If you want 1.1.1 for example? That clearly can't be represented as a float or double. Even with just major/minor, you have odd things - version 1.10 (the 11th minor version in major version 1) would be equal to 1.1. How is that useful? Using float or double for a version number is just wrong in my view. – Upstairs

I agree, but I see it used in quite a few API's - even Oracle ones. And switching on version nubmers is certainly a use case. But as said, it's a hack, and hacks should be avoided - I would consider it wrong as well. So maybe this is an additional reason to avoid the hack. There must be a Java puzzler somewhere in this :) – Almsgiver

@owlstead: I would certainly hate to see a language feature introduced because it would help in situations where an API had been badly designed. Ick, ick, ick. – Upstairs

@JonSkeet, I prefer switch over if-else because in switch, a jump table is created. So switch has a performance edge and it works slightly faster than if-else. – Baalbeer

@Aryan: I focus on correctness first - and floating point equality is hardly ever appropriate, so it makes sense that it isn't available in switch statements. It's not even clear that a jump table would be sensibly possible for a float... – Upstairs

@JonSkeet, actually I was talking about general switch working, not specifically focusing on floating point variables. – Baalbeer

@Aryan: Then it's not clear how it's related to this question/answer. And I wouldn't even prefer switch "in general" - I prefer whichever is most readable for the situation. – Upstairs

I was talking about this question which you asked in your answer - "I can't remember ever wanting to switch on any of these types, to be honest. Do you have a particular use case in mind?". – Baalbeer

@Aryan: Well that's specifically for float/double/boolean, as per the original question. Which of them were your referring to? – Upstairs

I was referring to other types too like int/string etc. I am sorry but I didn't notice that you were talking specifically about float/double/boolean. – Baalbeer

An example were you would want to switch case a boolean will be if you want to Switch on ranges of integers. For example: int x = 20; switch(true){ case x >0 && x <10 : ...; case x >10 && x <20: ... ; case x >20 && x <30: ... ; ....} . This is really useful. – Bratislava

@YakiKlein: That's moving way beyond just "switching on different types" though - that's now switching on expressions rather than constants. That's not what the question was about. – Upstairs

that's true. I did not think of it that way. – Bratislava

@JonSkeet, why are they supported in C#? – Issus

Answer 2

You can use enum in a switch statement and Java 7 will add String AFAIK. The switch statement comes from C where only int's were allowed and implementing other types is more complicated.

Floating point numbers are not a good candiates for switch as exact comparison is often broken by rounding errors. e.g. 0.11 - 0.1 == 0.01 is false.

switch on boolean is not much use as a plain if statement would be simpler

if(a) {

} else { 

}

would not be simpler with

switch(a) {
  case true:

     break;
  case false:

     break;
}

BTW: I would use switch(long) if it were available, but its not. Its a rare use case for me any way.

Powerhouse

Answer 3

For float and double float and double I'd assume they have omitted it for the same reasons as why it's a bad idea to compare them using ==.

For boolean, it may simply be because it would correspond to an if statement anyway. Remember that you can only have constants in the case-expressions, so the cases would always correspond to if (someBool) and if (!someBool).

For long I don't have an explanation. Seems to me that such feature perhaps should have been included when designing the language.

Unconstitutional

@aiodbe But would it be worth changing the language to support switch on long. That's a surprising amount of work for spectacularly little gain. (I guess why there wasn't switch on long in 1.0 is that it wouldn't fit with the existing pair of switch ops, so would either have to add two more pointless ops or provide a separate mechanism for compiling this case. And JDK 1.00 needed to ship to Netscape in six weeks.) – Loreeloreen

Ah, I agree completely. I guess I was trying to say "seems like a reasonable good idea to include". I know that the current ops are tied to ints so yes, it would probably involve a change in the bytecode set which is a huge thing to begin with. Updated the answer slighly. – Unconstitutional

Answer 4

Usually switch-case structure is used when executing some operations based on a state variable. There an int has more than enough options. Boolean has only two so a normal if is usually good enough. Doubles and floats aren't really that accurate to be used in this fashion.

Frankly I can't imagine a use case for this stuff, did you have some practical problem in mind with this question?

Withindoors

Answer 5

Had the same problem with a double and have a solution.

Within the switch braces you cast the double to a String and the do case "String". For example:

double d = 1.5
switch (String.valueOf(d)) {
       case "1.5": 
       break;
}

Flambeau

Answer 6

Yes, Java has not allowed boolean, double, and float in Switch Statement. The first thing is Switch Statement originally taken from C lang. and in C Switch statement only supports ti Integral Numbers to use in Switch. But Java Also Added a String in JAva7 to use in Switch to compare the predefined String. double and float double and float values can be rounded off any nearest value and becomes the whole number again, in this case, there might be the possibility of choosing two different cases in a switch statement, so it's a very bad idea to use double and float in a Switch statement.

boolean for true and false, we can use if and else, why use Switch again.? to find the correct case, the Switch statement will be searching for the case until it ends with the default case. so just for 2 cases, it's not needed to use a Switch statement.

Proudlove

What does this add to all the answers that are already given? Additionally, your "answer" is not written well ... – Sheltonshelty