Can there be multiple value assignments for the enhanced switch statement?

Question

I'm trying to initialize two variables with an enhanced switch statement:

int num = //something

boolean val1;
String val2;

val1, val2 = switch(num) {
    case 0 -> (true, "zero!");
    case 1 -> (true, "one!");
    default -> (false, "unknown :/");
}

Is this possible?

Answer 1

Since you are already on Java-13, I would suggest refraining from using an additional library to represent a tuple and make use ofMap.entry(introduced in Java-9) with the syntactic sugar of local variable type var inferred.

var entry = switch (num) {
    case 0 -> Map.entry(true, "zero!");
    case 1 -> Map.entry(true, "one!");
    default -> Map.entry(false, "unknown :/");
};
boolean val1 = entry.getKey();
String val2 = entry.getValue();

Answer 2

There’s not necessarily a benefit in cramming the initialization of two variables into one statement. Compare with

var val1 = switch(num) { case 0, 1 -> true; default -> false; };
var val2 = switch(num) { case 0 -> "zero!"; case 1 -> "one!"; default -> "unknown :/"; };

But for completeness, the new switch syntax does allow assignments too:

boolean val1;
String val2;
switch(num) {
    case 0 -> { val1 = true; val2 = "zero!"; }
    case 1 -> { val1 = true; val2 = "one!"; }
    default -> { val1 = false; val2 = "unknown :/"; }
}

You could also use the expression form to provide the initializer to one variable and assign the other

boolean val1;
String val2 = switch(num) {
    case 0 -> { val1 = true; yield "zero!"; }
    case 1 -> { val1 = true; yield "one!"; }
    default -> { val1 = false; yield "unknown :/"; }
};

but I wouldn’t be surprised if you don’t like it. For this specific example, it would also work to just use

var val2 = switch(num) { case 0 -> "zero!"; case 1 -> "one!"; default -> "unknown :/"; };
var val1 = !val2.equals("unknown :/");

Answer 3

There's no tuple unpacking in Java. A quick alternative that still uses a switch expression could use a custom class (using Pair in the following example):

Pair<Boolean, String> val = switch (num) {
    case 0 -> Pair.of(true, "zero!");
    case 1 -> Pair.of(true, "one!");
    default -> Pair.of(false, "unknown :/");
};

boolean val1 = val.getLeft();
String val2 = val.getRight();

Answer 4

Short answer, no, java does not support multiple assignment in any way as far as I'm aware. A workaround could be to buld a container class in witch to store both a string and bool.

example

class Response 
{
    String message;
    boolean found;
}

and return a object containing both.

Or potentially you could use an array and type casting, or a differently structured statement.

switch(num) {
    case 0: 
        val1 = true;
        val2 = "zero!"
        break;
    case 1: 
        val1 = true;
        val2 = "one!"
        break;
    default: 
        val1 = false;
        val2 = "unknown :/"
        break;
}

Answer 5

Another option (introduced as a preview feature in Java 14 and became a standard feature since Java 16) is to use a record as the container of the two values you wish to return.

This reduces the boilerplate code you'd have to write in order to create a regular class that holds the two values, while providing better readability compared to using the Map.Entry or Pair classes.

record Something (boolean boolField, String strField) {};

var result = switch(num) {
    case 0 -> new Something (true, "zero!");
    case 1 -> new Something (true, "one!");
    default -> new Something (false, "unknown :/");
};
boolean val1 = result.boolField ();
String val2 =  result.strField ();

Note that instead of Something, boolField and strField you should use meaningful names that describe the purpose of this record and its fields.