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Message:

pattern to eliminate switch statement

Posted by Tony Sintes on April 04, 2001 at 12:10 AM

The first step that you need to take is to reconsider your class structure. In a switch you normally case over some piece of data. Can you turn that data into an object.

Switch statements are a good indication that the object structure may be lacking (however, you cannot always avoid case).

Consider this switch:

void printDayOfTheWeek( int day_of_the_week ) {
switch (day_of_the_week)
{
case 1: System.out.println("Sunday");
break;
case 2: System.out.println("Monday");
... etc

Do this instead:

void printDayOfTheWeek( Day day ) {
System.out.println(day.day()); // where day returns the day as a string
}

Data validation is one place where it is difficult (if not impossible) to remove a switch. However, in other places, you need to turn your data into objects.

In OO you don't want to ask your objects to give you data and then process that data. Instead, you want to ask an object to do something to its data. switches generally break from this way of thinking.

Check out Refactoring by Martin Fowler for an entire section about killing switches.

Regards
Tony Sintes

> I have lot of 'switch' statements which really
> clutter up the place and cause very inflexible class design.

> Is there a design pattern which eliminates the need for te switch statements ?

> thanks
> Pat