Transforming if-else to lambda expression

Question

I'm trying to transform a simple if-else statement that I've found myself using all over the place to a more elegant lambda expression. But I'm having a hard time coming up with a solution from what I've been reading.

The simple statement goes like:

if (status.getStatus() == 'A') then
  handleA();
else if (status.getStatus() == 'B') then
  handleB();
else
  handleEverythingElse();

I know I could use the Command pattern with a map, but I'm sure there's some Java 8 elegance that I'm missing. Could someone show me the interface & impl, as well as it's usage in the body of the code (I learn by example)?

Any help would be much appreciated!

For starters you could use a switch statement... But why do you want a lambda anyway? If it works, don't fix it, right? — fge
– fge, Commented Aug 17, 2016 at 13:11
I think you are trying to overengineer your problem using some fancy new feature. In reality I don't think that it's a good idea, the only change to make is maybe use a switch instead of an if, even then I'm not sure if that's necessary. — puhlen
– puhlen, Commented Aug 17, 2016 at 13:14
Eh, so that is inside a switch. Time to rethink your approach, maybe? — fge
– fge, Commented Aug 17, 2016 at 13:15

GhostCat · Accepted Answer · 2016-08-17 13:19:04Z

2

If/else or even switch are not the "good OO design" answer. Neither are lambdas. Retrieving the status from somewhere, to make then a decision based on that - that is procedural programming; not OO.

You see, what you actually have in front of you - is a state machine. You have different states; and the point is: if your "thing" is in state A; then you want to do something ( invoke handleA() ). If your are in state B; you want to do something too ( like invoke handleB() ).

So, what you actually have is:

abstract class State {
  abstract void doIt();
...

StateA extends State {
  @Override
  void doIt() { handleA(); }

So, from the client side, you just call doIt() on same object of class State.

Thus: if you are really interested in improving your code base, learn how to use polymorphism to get rid of your if/else/switch statements.

You can watch this video to get an idea what I am talking about.

answered Aug 17, 2016 at 13:19

GhostCat

141k28 gold badges190 silver badges262 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Hovercraft Full Of Eels Over a year ago

Nice answer to what looks to be an XY Problem.

GhostCat Over a year ago

@HovercraftFullOfEels Thanks. I remember my own face when I first was told about something like that in my own code. To then figure: creating good OO designs especially around this kind of problems can be so rewarding ... that I can't resist to share such ideas as often as possible.

aatuc210 · Accepted Answer · 2016-08-22 12:35:08Z

Maybe I hadn't fully explained my problem, but my colleague proposed another solution that I really like. He suggested I make the if-else block a java.util.Supplier, and invoke it in the Entity class where I need it.

So my code went from this block of logic sprinkled everywhere:

public class ServiceImpl {
  ...
  if (entity.getStatus) == 'A' then
    finalStatus = handleA();
  else if (entity.getStatus() == 'B') then
    finalStatus = handleB();
  else
    finalStatus = handleEverythingElse();
  ...
}

To this nicely compacted form:

public class ServiceImpl {
  finalStatus = entity.getFinalStatus(this::handleStatus);

  public int handleStatus() {
    return dao.getStatus();
  }
}

With the implementation in my Entity class:

public class Entity {
  public int handleStatus(Supplier<Integer> s) {
    int finalStatus;
    if (status) == 'A' then
      finalStatus = handleA();
    else if (status() == 'B') then
      finalStatus = handleB();
    else
      finalStatus = supplier.get();
    return status;
  }
}

I hope this make sense...

Collectives™ on Stack Overflow

Transforming if-else to lambda expression

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related