How to check general conditions?

Question

I have translated a code from Matlab (array orientation) to Java(OOP). The problem appeared when I have to translate this feature of Matlab:

min_omegaF_restricted=min(omegaF(p>cost));

Here, omegaF is a vector with the net worth of each firm. p a vector of prices for each firm. cost a vector of costs for each firm. The above calculate the minimal net worth of survivor firms with demanded price higher than their costs. In java can be translated to:

double min_omegaF_restricted=Double.POSITIVE_INFINITY;
for(int f=0; f<F; f++){
    Firm fo=firms.get(f);
    if(fo.p>fo.cost)
        min_omegaF_restricted=Math.min(min_omegaF_restricted, fo.omegaF);
}

Is there a option to generalize this kind of sentence to whatever condition ( fo.p>fo.cost )?

Answer 1

Yes. Functional interfaces and lambdas in Java 8 make this simple and easy on the eyes. Create a Predicate which tests an object and returns a boolean value.

Predicate<Firm> predicate = firm -> firm.p > firm.cost;

Then you can defer to the predicate in the loop like so:

double min_omegaF_restricted=Double.POSITIVE_INFINITY;
for(int f=0; f<F; f++){
    Firm fo=firms.get(f);
    if(predicate.test(fo))
        min_omegaF_restricted=Math.min(min_omegaF_restricted, fo.omegaF);
}

What's more, with the new streaming API you can express the whole computation functionally without the explicit for loop.

double min_omegaF_restricted = firms.stream()
    .filter(predicate)
    .mapToDouble(f -> f.omegaF)
    .min()
    .orElse(Double.POSITIVE_INFINITY);