As of Java 14, the switch expression has an additional Lambda-like (case ... -> labels) syntax and it can be used not only as a statement, but also as an expression that evaluates to a single value.
Lambda-like syntax (case ... -> labels)
With the new Lambda-like sytax, if a label is matched, then only the expression or statement to the right of the arrow is executed; there is no fall through:
1 2 3 4 5 6 7 | var result = switch (str) { case "A" -> 1; case "B" -> 2; case "C" -> 3; case "D" -> 4; default -> throw new IllegalStateException("Unexpected value: " + str);}; |
The above is an example of switch as an expression returning an single integer value. The same syntax can be used in switch as a statement:
01 02 03 04 05 06 07 08 09 10 11 12 13 | int result;switch (str) { case "A" -> result = 1; case "B" -> result = 2; case "C" -> { result = 3; System.out.println("3!"); } default -> { System.err.println("Unexpected value: " + str); result = -1; }} |
yield
In the situation when a block is needed in a case, yield can be used to return a value from it:
1 2 3 4 5 6 7 8 9 | var result = switch (str) { case "A" -> 1; case "B" -> 2; case "C" -> { System.out.println("3!"); yield 3; // return } default -> throw new IllegalStateException("Unexpected value: " + str);}; |
Mutliple constants per case
It is also possible to use mutliple constants per case, separated by comma, which futher simplifies the usage of switch:
1 2 3 4 5 6 7 | var result = switch (str) { case "A" -> 1; case "B" -> 2; case "C" -> 3; case "D", "E", "F" -> 4; default -> 5;}; |
Final example
To demonstrate new switch syntax I created this tiny calculator:
01 02 03 04 05 06 07 08 09 10 11 12 13 14 | double calculate(String operator, double x, double y) { return switch (operator) { case "+" -> x + y; case "-" -> x - y; case "*" -> x * y; case "/" -> { if (y == 0) { throw new IllegalArgumentException("Can't divide by 0"); } yield x / y; } default -> throw new IllegalArgumentException("Unknown operator '%s'".formatted(operator)); };} |
Source code
The source code for this article can be found on Github: https://github.com/kolorobot/java9-and-beyond
References
Published on Java Code Geeks with permission by Rafal Borowiec, partner at our JCG program. See the original article here: Switch as an expression in Java with Lambda-like syntax Opinions expressed by Java Code Geeks contributors are their own. |
