captains-log

Captain's Log

Welcome to Captain's Log on Exercism's Java Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Randomness

An instance of the java.util.Random class can be used to generate random numbers in Java.

Random integers

A random integer can be generated using the nextInt() method. This will generate a value in the range from Integer.MIN_VALUE to Integer.MAX_VALUE.

Random random = new Random();

random.nextInt();
// => -1169335537

To limit the range of generated values, use nextInt(int). This will generate a value in the range from 0 (inclusive) to the given upper bound (exclusive).

For example, this will generate a random number from 0 through 9.

Random random = new Random();

random.nextInt(10);
// => 6

And this will generate a random number from 10 through 19.

Random random = new Random();

10 + random.nextInt(10);
// => 11

Random doubles

A random double can be generated using the nextDouble() method. This will generate a value in the range from 0.0 to 1.0.

Random random = new Random();

random.nextDouble();
// => 0.19250004204021398

And this will generate a random number from 100.0 to 200.0.

Random random = new Random();

100.0 + 100.0 * random.nextDouble();
// => 111.31849856260328

Instructions

Mary is a big fan of the TV series Star Trek: The Next Generation. She often plays pen-and-paper role playing games, where she and her friends pretend to be the crew of the Starship Enterprise. Mary's character is Captain Picard, which means she has to keep the captain's log. She loves the creative part of the game, but doesn't like to generate random data on the spot.

Help Mary by creating random generators for data commonly appearing in the captain's log.

The starter implementation of this exercise takes a `java.util.Random` instance as constructor argument.
This allows the exercise's tests to pass an instance with a predefined seed, which makes the test results predictable.

Therefore, you are expected to use the provided `java.util.Random` instance in your implementation.

1. Generate a random planet

The Starship Enterprise encounters many planets in its travels. Planets in the Star Trek universe are split into categories based on their properties. For example, Earth is a class M planet. All possible planetary classes are: D, H, J, K, L, M, N, R, T, and Y.

Implement the randomPlanetClass() method. It should return one of the planetary classes at random.

captainsLog.randomPlanetClass();
// => "K"

2. Generate a random starship registry number

Enterprise (registry number NCC-1701) is not the only starship flying around! When it rendezvous with another starship, Mary needs to log the registry number of that starship.

Registry numbers start with the prefix "NCC-" and then use a number from 1000 to 9999 (inclusive).

Implement the randomShipRegistryNumber() method that returns a random starship registry number.

captainsLog.randomShipRegistryNumber();
// => "NCC-1947"

3. Generate a random stardate

What's the use of a log if it doesn't include dates?

A stardate is a floating point number. The adventures of the Starship Enterprise from the first season of The Next Generation take place between the stardates 41000.0 and 42000.0. The "4" stands for the 24th century, the "1" for the first season.

Implement the randomStardate() method that returns a floating point number between 41000.0 (inclusive) and 42000.0 (exclusive).

captainsLog.randomStardate();
// => 41458.15721310934

Source

Created by

• @sanderploegsma

Contributed to by

• @santialb