Multiple values in switch case / converting ifs to switch statement

Question

I have a big list of Ifs, and I want to change it into a switch statement. Currently it looks like this:

if(x == 1){
    ...
}
if(x == 2){
    ...
}
if(myArray.contains(x)){
    ...
}

In actuality it's a bit longer than this, but it's the third if in the example that confuses me - how do I change that around to get it to work in a switch, or is it even possible?

Solution 1

You could do something like this, but YMMV according to possible exit conditions in your code:

switch (x) {
case 1: 
  ...
  break;
case 2:
  ...
  break;
case 3:
case 4:
  ... multi-case
  break;
default:
  if(myArray.contains(x)){
    ...
  }
}

Solution 2

Switch statement can be used only to test equality of x

So if not equality conditions like (if(myArray.contains(x))) must come at the end, then you can copy paste this into default section of switch

It would look this way

    switch (x) {
     case 1:   ...; break;
     case 2:   ...; break;
     default: if(myArray.contains(x)) ...
    }

If not equality conditions would need to be in the middle, then its not possible to use switch.

reference: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html

Solution 3

You can only swith over the x value. That means the last condition will not be part of the switch:

switch(x) {
case 1:
    ...
    break;
case 2:
    ...
    break;
}
if(myArray.contains(x)){
    ...
}

Solution 4

Yes, it is possible. The switch statement will make it a little cleaner and easier to maintain. You have to worry about x because it has to be compile-time constant.

switch(x) {
 case 1:
    doSomething();
    break();
 case 2:
    doSomethingElse();
    break();

default:
 if(myArray.contains(x)){

 }


//etc...
}

View more solutions

Comments

[rds]

This is also slightly different: switch/case is a if ... else if. In the siutation where x is modified in a "then" block statement, the overall behaviour will be different.

[Anthony Grist]

Unlike the first two ifs in the question, the third can still be true even if one of the preceding ones is also true. x can't be equal to 1 AND 2 at the same time, but it can be equal to 1 and contained within myArray at the same time. Moving the if statement into the case statements default is likely not the correct solution.

[Steve]

Sorry I should have clarified - the values in the array will never match anything else that I'm checking for, so it's not an issue. good catch though.

[solendil]

You're both right, that's why I told YMMV... I assumed that the code in every if had an exit. Orelse the original code looks like a plate of spaghettis. Multiple ifs, each modifying the variable for itself and the next if, no elsif, a final condition that seems logically unrelated. The meaning of the original code is far from clear, so there's no straightforward translation for it. My answer provide a possible solution, but only the original poster will know if it suits his needs.