In Java 12, the switch statement has been enhanced so that it can be used as an expression. It is now also possible to switch on multiple constants in a single case, resulting in code that is more concise and readable. These enhancements are a preview language feature, which means that they must be explicitly enabled in the Java compiler and runtime using the --enable-preview flag.
Consider the following switch statement:
int result = -1;
switch (input) {
case 0:
case 1:
result = 1;
break;
case 2:
result = 4;
break;
case 3:
System.out.println("Calculating: " + input);
result = compute(input);
System.out.println("Result: " + result);
break;
default:
throw new IllegalArgumentException("Invalid input " + input);
}
In Java 12, this can be rewritten using a switch expression as follows:
final int result = switch (input) {
case 0, 1 -> 1;
case 2 -> 4;
case 3 -> {
System.out.println("Calculating: " + input);
final int output = compute(input);
System.out.println("Result: " + output);
break output;
}
default -> throw new IllegalArgumentException("Invalid input " + input);
};
As illustrated above:
- The
switchis being used in an expression to assign a value to theresultinteger - There are multiple labels separated with a comma in a single
case - There is no fall-through with the new
case X ->syntax. Only the expression or statement to the right of the arrow is executed - The
breakstatement takes an argument which becomes the value returned by theswitchexpression (similar to areturn)
