Use the switch statement to conditionally perform statements
based on an integer expression. For example, suppose that your program
contained an integer named month whose value indicated the
month in some date. Suppose also that you wanted to display the name of
the month based on its integer equivalent. You could use Java's
switch statement to perform this feat:
int month;
. . .
switch (month) {
case 1: System.out.println("January"); break;
case 2: System.out.println("February"); break;
case 3: System.out.println("March"); break;
case 4: System.out.println("April"); break;
case 5: System.out.println("May"); break;
case 6: System.out.println("June"); break;
case 7: System.out.println("July"); break;
case 8: System.out.println("August"); break;
case 9: System.out.println("September"); break;
case 10: System.out.println("October"); break;
case 11: System.out.println("November"); break;
case 12: System.out.println("December"); break;
}
The switch statement evaluates its expression,
in this case, the value of month, and executes the
appropriate case statement. Of course, you could
implement this as an if statement:
int month;
. . .
if (month == 1) {
System.out.println("January");
} else if (month == 2) {
System.out.println("February");
. . .
// you get the idea
. . .
Deciding whether to use an if statement or a switch
statement is a judgment call.
You can decide which to use based on readability and other factors.
An if statement can be used to make decisions
based on ranges of values or conditions,
whereas a switch statement can make decisions
based only on a single integer value.
Also, the value provided to each case statement must be unique.
Another point of interest in the switch statement are the
break statements after each case. The break
statements cause control to break out of the switch and continue
with the first statement following the switch.
The break statements are necessary because case
statements fall through. That is, without an explicit break
control will flow sequentially through subsequent case statements.
In the previous example, you don't want control to flow from one case
to the next, so you have to put in break statements.
However, there are certain scenarios when you do want control to proceed
sequentially through case statements. Like in the following Java code that
computes the number of days in a month according to the old rhyme that
starts "Thirty days hath September...":
int month;
int numDays;
. . .
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
numDays = 31;
break;
case 4:
case 6:
case 9:
case 11:
numDays = 30;
break;
case 2:
if ( ((year % 4 == 0) && !(year % 100 == 0))
|| (year % 400 == 0) )
numDays = 29;
else
numDays = 28;
break;
}
Finally, you can use the default statement at the end of the
switch to handle all values that aren't explicitly handled
by one of the case statements.
int month;
. . .
switch (month) {
case 1: System.out.println("January"); break;
case 2: System.out.println("February"); break;
case 3: System.out.println("March"); break;
case 4: System.out.println("April"); break;
case 5: System.out.println("May"); break;
case 6: System.out.println("June"); break;
case 7: System.out.println("July"); break;
case 8: System.out.println("August"); break;
case 9: System.out.println("September"); break;
case 10: System.out.println("October"); break;
case 11: System.out.println("November"); break;
case 12: System.out.println("December"); break;
default: System.out.println("Hey, that's not a valid month!");
break;
}
