High Order Filtering [duplicate]

1. How to remove the duplicates from array without changing order?
2. Is reuse a higher-order function?
3. Why filter is a higher-order function?

How to remove the duplicates from array without changing order?

Iterate through array (via iterator, not foreach) and remove duplicates. Use set for find duplicates. Iterate through array and add all elements to LinkedHashSet, it isn't allows duplicates and keeps order of elements. Then clear array, iterate through set and add each element to array.

Is reuse a higher-order function?

We can again use the concept of higher order functions to make a simple, reusable higher order function that is able to make one pass through the entire list of frogs by applying the filters at the same time.

Why filter is a higher-order function?

In functional programming, filter is a higher-order function that processes a data structure (usually a list) in some order to produce a new data structure containing exactly those elements of the original data structure for which a given predicate returns the boolean value true .