zaidrehman / techtest

TechTest

Question 1

What is the difference in how structs and classes are passed into methods? What is safer to use, and why? Explain with an example in your own words

Ans:

Structs default access specifier is public but default access specifier of class is private so attributes of the class should be made public so that they can be modified or accessed from methods of other classes (line 6 in our example.cpp).

Passing by Value is safer than passing by Reference because in the Parallelized application when using Passing by Reference we need a locking mechanism but there is no such limitation in Passing by Value .

Question 2

In Java, how are callbacks implemented? Demonstrate with an Object that prints the reverse of a String in a callback, upon receiving a String.

Ans:

Callback function is used in functional programming, a function is passed to a higher order function like an argument and the higher order function executes it when required (When the criteria are met).

We can implement it by passing an implementation of an Interface to our system which is responsible for triggering an Event. A Callback function is called when this event is triggered.(Code is in the example.java)

Question 3

What is the difference between Array#filter and Array#map methods?

Ans:

Filter lets you provide a callback for every element and returns a filtered array. Filter executes the callback and check its return value. If the value is true element remains in the resulting array else removed for the resulting array. Filter never changes the value of the element and filter may result in reducing the size of the array.

Map takes a callback and runs it against all the elements on the array and creates a new array with the desired output. Map never reduces the size of the array as no element gets removed.It updates all the elements according to the callback specified.

What does the follow piece of code do, and how?

  if (arr.map(str => str.length > 0).filter(x => x).length > 0) {
  …
  }

Ans:

Let's solve by breaking it. arr.map(str => str.length > 0) will return a boolean array where all elements having a length greater than zero will be true and rest will be false.

This boolean array output will be the input for .filter(x => x) and it will return another boolean array with only the elements whos value is true. filter(x => x).length > 0 will return true if the newly created array has length more than 0 else it will return false.

Example :

arr = ["aa","","bbb","aqws","aaa"]
arr.map(str => str.length > 0)

OUTPUT: (5) [true, false, true, true, true]

arr.map(str => str.length > 0).filter(x => x)

OUTPUT: (4) [true, true, true, true]

arr.map(str => str.length > 0).filter(x => x).length > 0

OUTPUT: true