Java If Statement

Question

I have written some code in Java which tests the fitness of two solutions.

I am looking to then compare the two solutions and keep the one which has the best fitness and to discard the other.

For example:

if(fitness1 < fitness2)
    keep fitness1 and discard/ignore fitness2
else
    keep fitness2 and discard/ignore fitness1

How would I go about achieving this? Eventually I hope to have a list (size n) of the best fitness levels. I imagine that I would have to add the best fitness in each iteration to a list of some type?

Could you be more specific? What kind of variable is the fitness (int, double, etc.)? — Rafe Kettler
– Rafe Kettler, Commented Mar 25, 2011 at 17:51
fitness1 and fitness2 are both double variables. discard just means 'ignore' - I am only looking to keep track of the best fitness level. — Mus
– Mus, Commented Mar 25, 2011 at 17:52
This looks like a very very basic Java question. Have you read tutorials about basic Java syntax, especially declaring and assigning variables? — MAK
– MAK, Commented Mar 25, 2011 at 17:53
Are greater or lesser numbers better? Your current comparison would imply that a lower fitness score is better than a higher one (which may very well be the case, of course). — eldarerathis
– eldarerathis, Commented Mar 25, 2011 at 17:54
What kind of data are fitness1 and fitness2? What do you mean by "discard"? Java has automatic garbage collection, so you don't need to do anything to discard an object; just don't keep a reference to it. — Ted Hopp
– Ted Hopp, Commented Mar 25, 2011 at 17:56

Maciej Ziarko · Accepted Answer · 2011-03-25 17:52:20Z

6

best = (fitness1 < fitness2) ? fitness1 : fitness2;

?: ternary operator may be useful in this kind of decision making process.

answered Mar 25, 2011 at 17:52

Maciej Ziarko

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4 Comments

user395760 Over a year ago

Which is a convulted and hardly scaling way to reinvent min.

Jesus Ramos Over a year ago

Wish i could +2 this, don't see enough ternary operators in Java :D

Ted Hopp Over a year ago

Seems like a baroque way of writing best = Math.min(fitness1, fitness2);

Maciej Ziarko Over a year ago

I have C/C++ background and ?: was made available in Java especially for people like me. I like it and I'm used to it. :) Of course both methods are OK.

tvkanters · Accepted Answer · 2011-03-25 17:54:20Z

3

I'd say, create an ArrayList<Double> to keep the best values in and use this:

arrayList.add((fitness1 < fitness2) ? fitness1 : fitness2);

That way you'll have a list of the best values.

answered Mar 25, 2011 at 17:54

tvkanters

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1 Comment

tvkanters Over a year ago

Though I don't see any duplicate results in the example output, could you show what algorithm you're using to go through the possible fitness values?

Rob Hruska · Accepted Answer · 2011-03-25 18:19:54Z

1

If your end goal is to have a list of the "top n fitness levels", you'll probably have a list of them coming in, right?

If that's the case, just leverage the capabilities of List:

// takes a list of Doubles, returns 'top' levels
public List<Double> getTopN(List<Double> allLevels, int top) {
    List<Double> sorted = new ArrayList<Double>(allLevels); // defensive copy
    Collections.sort(sorted, new Comparator<Double>() {
        @Override
        public int compare(Double left, Double right) {
            return left.compareTo(right); // assumes no null entries
        }
    });

    return sorted.subList(0, Math.min(sorted.size(), top));
}

answered Mar 25, 2011 at 18:19

Rob Hruska

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Comments

brian_d · Accepted Answer · 2011-03-25 17:52:46Z

0

Introduce another variable.

type bestFitness

if(fitness1 < fitness2){
   bestFitness = fitness1;
}else{
   bestFitness = fitness2;
}

Then discard both fitness1, fitness2

Or use Math.min

answered Mar 25, 2011 at 17:52

brian_d

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Comments

Amir Afghani · Accepted Answer · 2011-03-25 17:55:45Z

0

Assuming the fitness is an int

int fitness1 = 5;
int fitness2 = 10;

int bestFit = bestFit(fitness1, fitness2);

//nothing needs to be done to explicitly discard fitness2.  Just keep using bestFit
//and let the GC worry about discarding stuff for you

public static int bestFit(int f1, int f2) { 

   return f1 > f2 ? f1 : f2

}

answered Mar 25, 2011 at 17:55

Amir Afghani

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