java: A long list of conditions , what to do? [closed]

Question

I need suggestion for the right approach to apply conditions in Java.

I have 100 conditions based on which I have to change value of a String variable that would be displayed to the user.

an example condition: a<5 && (b>0 && c>8) && d>9 || x!=4

More conditions are there but variables are the same more or less.

I am doing this right now:

    if(condition1)
    else if(condition2)
    else if(condition3)
    ...

A switch case alternative would obviously be there nested within if-else's i.e.

if(condition1)
 switch(x)
  {
   case y:
     blah-blah
   }        
else if(condition2)
switch(x)
  {
   case y:
     blah-blah
   }  
else if(condition3)
...

But I am looking for some more elegant solution like using an Interface for this with polymorphic support , What could be the thing that I could possibly do to avoid lines of code or what should be the right approach.

---Edit---

---

I actualy require this on an android device. But its more of a java construct here.

This is a small snapshot of conditions that I have with me. More will be added if a few pass/fail. That obviously would require more if-else's with/without nesting. In that case would the processing go slow.

I am as of now storing the messages in a separate class with various string variables those I have kept static so if a condition gets true then I pick the static variable from the only class and display that one. Would that be right about storing the resultant messages.

Answer 1

Depending on the number of conditional inputs, you might be able to use a look-up table, or even a HashMap, by encoding all inputs or even some relatively simple complex conditions in a single value:

int key = 0;

key |= a?(1):0;
key |= b?(1<<1):0;
key |= (c.size() > 1)?(1<<2):0;
...

String result = table[key]; // Or result = map.get(key);

This paradigm has the added advantage of constant time (O(1)) complexity, which may be important in some occasions. Depending on the complexity of the conditions, you might even have fewer branches in the code-path on average, as opposed to full-blown if-then-else spaghetti code, which might lead to performance improvements.

We might be able to help you more if you added more context to your question. Where are the condition inputs coming from? What are they like?

And the more important question: What is the actual problem that you are trying to solve?

Answer 2

There are a lot of possibilities to this. Without knowing much about your domain, I would create something like (you can think of better names :P)

 public interface UserFriendlyMessageBuilder {
      boolean meetCondition(FooObjectWithArguments args);

      String transform(String rawMessage);
 }

In this way, you can create a Set of UserFriendlyMessageBuilder and just iterate through them for the first that meets the condition to transform your raw message.

public class MessageProcessor {
    private final Set<UserFriendlyMessageBuilder> messageBuilders;

    public MessageProcessor(Set<UserFriendlyMessageBuilder> messageBuilders) {
        this.messageBuilders = messageBuilders;
    }

    public String get(FooWithArguments args, String rawMsg) {

        for (UserFriendlyMessageBuilder msgBuilder : messageBuilders) {
            if (msgBuilder.meetCondition(args)) {
                return msgBuilder.transform(rawMsg);
            }
        }
        return rawMsg;    
    }
}