Java: Enum parameter in method

Question

I have a method lets say:

private static String drawCellValue(
    int maxCellLength, String cellValue, String align) { }

and as you can notice, I have a parameter called align. Inside this method I'm going to have some if condition on whether the value is a 'left' or 'right'.. setting the parameter as String, obviously I can pass any string value.. I would like to know if it's possible to have an Enum value as a method parameter, and if so, how?

Just in case someone thinks about this; I thought about using a Boolean value but I don't really fancy it. First, how to associate true/false with left/right ? (Ok, I can use comments but I still find it dirty) and secondly, I might decide to add a new value, like 'justify', so if I have more than 2 possible values, Boolean type is definitely not possible to use.

Any ideas?

Answer 1

This should do it:

private enum Alignment { LEFT, RIGHT };    
String drawCellValue (int maxCellLength, String cellValue, Alignment align){
  if (align == Alignment.LEFT)
  {
    //Process it...
  }
}

Answer 2

Even cooler with enums you can use switch:

switch (align) {
   case LEFT: { 
      // do stuff
      break;
   }
   case RIGHT: {
      // do stuff
      break;
   }
   default: { //added TOP_RIGHT but forgot about it?
      throw new IllegalArgumentException("Can't yet handle " + align);

   }
}

Enums are cool because the output of the exception will be the name of the enum value, rather than some arbitrary int value.

Answer 3

I like this a lot better. reduces the if/switch, just do.

private enum Alignment { LEFT, RIGHT;

void process() {
//Process it...
} 
};    
String drawCellValue (int maxCellLength, String cellValue, Alignment align){
  align.process();
}

of course, it can be:

String process(...) {
//Process it...
} 

Answer 4

Sure, you could use an enum. Would something like the following work?

enum Alignment {
    LEFT,
    RIGHT
}

private static String drawCellValue(int maxCellLength, String cellValue, Alignment alignment) { }

If you wanted to use a boolean, you could rename the align parameter to something like alignLeft. I agree that this implementation is not as clean, but if you don't anticipate a lot of changes and this is not a public interface, it might be a good choice.

Answer 5

You could also reuse SwingConstants.{LEFT,RIGHT}. They are not enums, but they do already exist and are used in many places.

Answer 6

I am not too sure I would go and use an enum as a full fledged class - this is an object oriented language, and one of the most basic tenets of object orientation is that a class should do one thing and do it well.

An enum is doing a pretty good job at being an enum, and a class is doing a good job as a class. Mixing the two I have a feeling will get you into trouble - for example, you can't pass an instance of an enum as a parameter to a method, primarily because you can't create an instance of an enum.

So, even though you might be able to enum.process() does not mean that you should.

Answer 7

You can use an enum in said parameters like this:

public enum Alignment { LEFT, RIGHT }
private static String drawCellValue(
int maxCellLength, String cellValue, Alignment align) {}

then you can use either a switch or if statement to actually do something with said parameter.

switch(align) {
case LEFT: //something
case RIGHT: //something
default: //something
}

if(align == Alignment.RIGHT) { /*code*/}