Paralleelprogrammeerimise keeled 2022/23 sügis

Java (parallel) streams

Use the Java tutorial on Aggregate Operations as a reference if you are unsure.

1. Given a list of names like (william, jones, aaron, bob, frank, gillian), calculate using streams the sum of the letters of all names longer than 4 letters.
2. Calculate the sum of all even numbers from 2 to a given number N using streams. Ideally, do not manually generate the list of numbers.
3. Given a class Person as below, print the age of the oldest person in a list of Persons using streams.
4. Using the same class, print the name of the oldest person in a list of Persons using streams.

class Person {

	private String name;
	private int age;
	private String nationality;

	public Person(String name, int age, String nationality) {
		this.name = name;
		this.age = age;
		this.nationality = nationality;
	}

	public Person(String name, int age) {
		this(name, age, "");
	}

	public String getName() {
		return name;
	}

	public int getAge() {
		return age;
	}

  public String getNationality() {
    return nationality;
  }
}

Parallel streams doing real work

Most of this is from lab 3, the description is repeated for convenience.

We want to find the number of divisors of the number in a range of positive numbers which has the maximum number of divisors. A divisor is a number which divides another number with remainder 0. For example, 9 has two divisors, namely 3 and 1, whereas 8 has three, namely 1,2, and 4 (if the 1 is included or not does not matter for the maximum). Using the int data type should be enough for this exercise.

As a first step, write a program which finds the divisors for a number.

Then extend this to find the maximum number of divisors for a range in a sequential fashion. Try this out for eg the range from 1 to 1000 and 1 to 100,000 and 1 to 10,000,000. Record how long it takes for 1 to 10,000,000.

Finally, implement a concurrent version using parallel streams. How much of an speedup do we have?