Switch as an expression in Java with Lambda-like syntax
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:
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:
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:
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:
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:
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
