Enhanced Switch

From Java SE 12, a new and enhanced version of the switch statement is available. Consider the example below

switch (monthNum) {
    case 2:
        System.out.println("28 days");
        break;
    case 1: case 3: case 5: case 7: case 8: case 10: case 12:
        System.out.println("31 days");
        break;
    case 4: case 6: case 9: case 11:
        System.out.println("30 days");
}

Two keywords are repeated: case many times, and break twice (though break can appear many times in longer switch statements)

The enhanced switch statement allows us to seperate multiple case values using a comma, and, where the code is a sinlge line for a statement, doesn't require use of the of the break keyword - there is no fall through. The above code is rewritten below in the new format

switch (monthNum)
{
    case 2 -> System.out.println("28 days");
    case 1,3,5,7,8,10,12 -> System.out.println("31 days");
    case 4, 6, 9, 11 -> System.out.println("30 days");
}

Assigning values

If, rather than printing the message showing the number of days in a week, we wanted to store it in a variable, instead of printing inside the switch statement, we could assign it to a variable, for example:

String message = "";
switch (monthNum)
{
    case 2 -> message = "28 days";
    case 1,3,5,7,8,10,12 -> message = "31 days";
    case 4, 6, 9, 11 -> message = "30 days";
}

System.out.println(message); 

This approach works with both the new and original switch statement

The enhanced statement allows us to go on step further and reduce the duplication of the message = element of the code. Provided every possible case is considered, we can assign the result of calling the switch statement to a variable. In the above code, we only consider values from 1-12 inclusive, therefore to consider any other integer value, we need a default clause. Adding the default clause, and assigning to a variable would look like this:

String message = switch (monthNum)
{
    case 2 -> "28 days";
    case 1,3,5,7,8,10,12 -> "31 days";
    case 4, 6, 9, 11 -> "30 days";
    default -> "not a valid month number";
};
System.out.println(message);

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