Here are some JAVA Problems

$--$For each of the following exercises provide a solution that uses methods of

the Stream interface.

$1$

Write a method getElement implementing a partial function that given an

array arr and an int index returns arr$[$index$]$ if defined. Use Optional as the result

type. Next write methods implementing the following partial functions:

$$ sqrt$,$ that applied to an integer returns its square root as a double, if the

argument is not negative;

$$ half, that applied to an integer returns its half as an integer, if the argument is

even.

Finally write a method that composing getElement, sqrt and half, when applied to an

array of integers arr and to an int index, returns the square root of the half

of arr$[$index$],$ if defined.

$2$

Consider the attached csv file people.csv$.$ This file stores information about people

subscribed to a simple service. Each line of the file represents a record. The fields of

each record are separated by a comma $","$ and have the following meaning

id$,$firstname,surname,title,address,town,country,postcode,subscription

paid,gender,date of birth

In a record the fields id$,$ firstname, surname, date of birth, subscription paid are

mandatory, while the others are optional $($denoted by $"-"$ in the file$).$ Implement a

class Subscriber representing a subscriber, providing a property for each field. Use

the Optional class to denote optional fields.

Write a static method loadDatabase that returns a List containing the

records of the file subscriber.csv$.$ Furthermore, implement another static

method PaymentFromGB that given a List prints the subscribers from GB

that have paid the annual fee.

Hint: Use the methods of Optional class to deal with optional values.