Arian :
I have a bunch of methods that are basically doing the same thing: selecting top N instances of a class based on value returned by its different methods all returning double value.
So for example, for objects of a class implementing the following interface:
interface A {
Double getSalary();
Double getAge();
Double getHeight();
}
I want to select N objects with the highest of values returned by each method.
Right now I have 3 methods:
List<A> getTopItemsBySalary(List<A> elements);
List<A> getTopItemsByAge(List<A> elements);
List<A> getTopItemsByHeight(List<A> elements);
That has this body:
List<A> getTopItemsBySalary(List<A> elements, int n) {
return elements.stream()
.filter(a -> a.getSalary() != null)
.sorted(Comparator.comparingDouble(A::getSalary).reversed())
.limit(n)
.collect(Collectors.toList());
}
How can I pass in the method and just have one method?
ernest_k :
You can use a Function that converts A to Double, like:
List<A> getTopItems(List<A> elements, Function<A, Double> mapper, int n) {
return elements.stream()
.filter(a -> null != mapper.apply(a))
.sorted(Comparator.<A>comparingDouble(a -> mapper.apply(a))
.reversed())
.limit(n)
.collect(Collectors.toList());
}
And you can call it using:
List<A> top10BySalary = getTopItems(list, A::getSalary, 10);
List<A> top10ByAge = getTopItems(list, A::getAge, 10);
If your getters are expected to always return a non-null, then ToDoubleFunction is a better type to use (but it won't work if your Double return values may be null):
List<A> getTopItems(List<A> elements, ToDoubleFunction<A> mapper, int n) {
return elements.stream()
.sorted(Comparator.comparingDouble(mapper).reversed())
.limit(n)
.collect(Collectors.toList());
}
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