Switch Statement Quotes

Question

With Java, I'm reading a book to re-cover the basics I forgot in college, and they're showing me a swtich statement like so:

void helpon(int what) {
    switch(what) {
        case '1': break;
        case '2': break;
    }
}

I omitted case code because irrelevant.

However, it seemed odd to me to use an int and still wrap the case statements in single quotes, so I went to the oracle docs and found an example that was the same as the example above, but without the quotes.

Do quotes matter for a switch statement that uses integers as a case? Why would '1' work, if what is an int and '1' is a char?

Answer 1

Single quoted characters are literal chars and char values fall in int values. A char can be represented as an int from its UTF-16 value, for example:

char c = '1';
int i = c;
System.out.println(i);

Output:

49

More info:

• Java Tutorials: Primitive Data Types

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Do not get confused between ASCII characters (single byte, value from 0 to 127) and UTF-16 (2 bytes per code point, value from 0 to 65535). More info: Unicode, UTF, ASCII, ANSI format differences

Answer 2

I just want to add some depth. Yes '1' is the char of 1 which is stored as an int value and that is why you can use an int in a char declaration (single quotes is the other way to do it). However, char is stored as a range with a maximum of 65,535 (Java is utf-16 I believe so 2^16). You cannot have a negative int value in char without casting and casting will yield an odd character. A value greater than the range is a problem.

A switch will take the following int,char,short,byte (anything that fits in an int) and with SE7 a String. Basically, the primitives and a String object are acceptable. You could turn the primitive into an object such as Integer, Character,Short;Byte.

Technically with char you can use either int within range or a char for the case as long as you are checking the right thing.

With an int anything that automatically fits into an int should be used. Casting in the switch parameter causes a loss of precision.

For good measure, don't forget to break or you will fall through. Also, the case statements must be constants determinable at compile time, either arithmetic of known and acceptable primitives, a known primitive using the final modifier, or a directly coded constant.