Is byte, short, char automatically promoted in switch statement?

Question

Given the following code, is 'a' (that is of type char) automatically promoted to int type in switch-case statement?

void testSwitch(byte x) {
    switch(x) {
       case 'a':   // 1
       case 256:   // 2
       default:   //  3
       case 1:    //  4
    }

}

I couldn't find whether Java SE7 mentions about that..

Thanks in advance for clarification.

Regards, Daniel

switch takes an `int` and byte, char, and short can be automatically widened whenever needed. — Peter Lawrey, Feb 11 '16 at 20:35
[the type of `0`](https://groups.google.com/forum/#!topic/java-lang-fans/0zGzPygyJSU) — ZhongYu, Feb 11 '16 at 21:07

score 7 · Accepted Answer · edited Jun 20 '20 at 09:12

7

Here's what the language specification mentions about this. See this section on switch statements:

Given a switch statement, all of the following must be true or a compile-time error occurs:

Every case constant associated with the switch statement must be assignment compatible with the type of the switch statement's Expression (§5.2).

...

which means that a narrowing conversion will apply to the char value 'a'. Its numeric value of 97 is representable as a byte. The value 256 however does not fit so the compiler will throw an error.

edited Jun 20 '20 at 09:12

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answered Feb 11 '16 at 20:31

M A

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Thanks @AR.3. Good clarification. It is a point worth remembering :) – yegomosc Feb 11 '16 at 20:40

score 0 · Answer 2 · edited May 23 '17 at 11:52

0

Yes the switch statement will generate tableswitch or lookupswitch primitives with constants which are promoted to int generally according to this

http://blog.jamesdbloom.com/JavaCodeToByteCode_PartOne.html

Why does the Java API use int instead of short or byte?

edited May 23 '17 at 11:52

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answered Feb 11 '16 at 20:35

aoa

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Is byte, short, char automatically promoted in switch statement?

2 Answers2