function interface in Java

A Function interface is more of a generic one that takes one argument and produces a result. This has a Single Abstract Method (SAM) apply which accepts an argument of a type T and produces a result of type R. 
There are many versions of Function interfaces because a primitive type can’t imply a general type argument, so we need these versions of function interfaces. Many different versions of the function interfaces are instrumental and are commonly used in primitive types like double, int, long. The different sequences of these primitive types are also used in the argument.
The BiFunction is substantially related to a Function. Besides, it takes two arguments, whereas Function accepts one argument. 
One of the common use cases of this interface is Stream.map method. 
```
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("a", "ab", "abc", "de", "efg");
        Function<String, Integer> nameMappingFunction = String::length;
        List<Integer> nameLength = names.stream().map(nameMappingFunction).collect(Collectors.toList());
        System.out.println(nameLength); // [1, 2, 3, 2, 3]
    }
}
```
Home