Java

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Exercism
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Free Online Course
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English
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Beginner

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Java is among the most popular available programming languages, thanks to its versatility and compatibility. It is widely used for software development, mobile applications and developing larger systems. Java was born in 1995 and is maintained by Oracle. Despite the fact that it isn't as young as some of the fresh languages out there, Java is still really popular. It was designed to be fast, secure, reliable, beginner-friendly and highly portable. This portability perk exists because Java is executed on a cross-platform compatible . Android apps are also developed using Java, since the runs on a Java language environment.

Syllabus

Hello World

Exercism's classic introductory exercise. Just say "Hello, World!".

Cook Your Lasagna

Learn about the basics of Java by following a lasagna recipe.

Annalyn's Infiltration

Learn about booleans while helping Annalyn rescue her friend.

Bird Watcher

Learn about arrays by keeping track of how many birds visit your garden.

Karl's Languages

Learn about lists by helping Karl keep track of the languages he wants to learn on Exercism.

Calculator Conundrum

Learn about exception-handling by making a simple calculator.

Squeaky Clean

Learn about characters and StringBuilder by cleaning strings.

Jedlik's Toy Car

Learn about classes by working on a remote controlled car.

Need for Speed

Learn about classes by creating cars.

Remote Control Competition

Learn about interfaces by working on cars.

Cars, Assemble!

Learn about numbers by analyzing the production of an assembly line.

Log Levels

Learn about strings by processing logs.

Salary Calculator

Learn about ternary operators by calculating salaries.

Football Match Reports

Learn about switches by developing a system to report on soccer matches.

Wizards and Warriors

Learn about inheritance by creating an RPG.

Logs, Logs, Logs!

Learn about enums by parsing logs.

Tim from Marketing

Learn about the null literal and nullable variables in java by printing name badges.

Captain's Log

Learn about randomness by helping Mary generate stardates and starship registry numbers for her Star Trek themed pen-and-paper role playing sessions.

Booking Up For Beauty

Learn about the LocalDate and LocalDateTime classes by working on an appointment scheduler for a beauty salon.

Wizards and Warriors 2

Learn about method overloading by extending your favorite RPG.

Secrets

Learn about bit manipulation by writing a program to decrypt a message.

Gotta Snatch 'Em All

Learn to use sets by playing a vintage trading card game

International Calling Connoisseur

Learn about maps while managing international calling codes.

Leap

Determine whether a given year is a leap year.

Reverse String

Reverse a given string.

Two Fer

Create a sentence of the form "One for X, one for me.".

Armstrong Numbers

Determine if a number is an Armstrong number.

Darts

Calculate the points scored in a single toss of a Darts game.

D&D Character

Randomly generate Dungeons & Dragons characters.

DOT DSL

Write a Domain Specific Language similar to the Graphviz dot language.

Grains

Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.

High Scores

Manage a player's High Score list.

Resistor Color

Convert a resistor band's color to its numeric representation.

Resistor Color Duo

Convert color codes, as used on resistors, to a numeric value.

Resistor Color Trio

Convert color codes, as used on resistors, to a human-readable label.

RNA Transcription

Given a DNA strand, return its RNA complement.

Acronym

Convert a long phrase to its acronym.

Difference of Squares

Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.

Gigasecond

Given a moment, determine the moment that would be after a gigasecond has passed.

Hamming

Calculate the Hamming distance between two DNA strands.

Micro Blog

Given an input string, truncate it to 5 characters.

Pangram

Determine if a sentence is a pangram.

Perfect Numbers

Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for positive integers.

Eliud's Eggs

Help Eliud count the number of eggs in her chicken coop by counting the number of 1 bits in a binary representation.

Protein Translation

Translate RNA sequences into proteins.

Raindrops

Convert a number into its corresponding raindrop sounds - Pling, Plang and Plong.

Given a number from 0 to 999,999,999,999, spell out that number in English.

Scrabble Score

Given a word, compute the Scrabble score for that word.

Secret Handshake

Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.

Space Age

Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.

Collatz Conjecture

Calculate the number of steps to reach 1 using the Collatz conjecture.

Diamond

Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.

Error Handling

Implement various kinds of error handling and resource management.

ISBN Verifier

Check if a given string is a valid ISBN-10 number.

Isogram

Determine if a word or phrase is an isogram.

Killer Sudoku Helper

Write a tool that makes it easier to solve Killer Sudokus

Kindergarten Garden

Given a diagram, determine which plants each child in the kindergarten class is responsible for.

Largest Series Product

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

Luhn

Given a number determine whether or not it is valid per the Luhn formula.

Matrix

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

Nth Prime

Given a number n, determine what the nth prime is.

Proverb

For want of a horseshoe nail, a kingdom was lost, or so the saying goes. Output the full text of this proverbial rhyme.

Rate Limiter

Practice stateful logic and time handling by implementing a fixed-window rate limiter

Rotational Cipher

Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.

Saddle Points

Detect saddle points in a matrix.

Sieve

Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.

Split-Second Stopwatch

Keep track of time through a digital stopwatch.

Sum of Multiples

Given a number, find the sum of all the multiples of particular numbers up to but not including that number.

Swift Scheduling

Convert delivery date descriptions to actual delivery dates.

Triangle

Determine if a triangle is equilateral, isosceles, or scalene.

Twelve Days

Output the lyrics to 'The Twelve Days of Christmas'.

Variable Length Quantity

Implement variable length quantity encoding and decoding.

Yacht

Score a single throw of dice in the game Yacht.

Allergies

Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.

Atbash Cipher

Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.

Bob is a lackadaisical teenager. In conversation, his responses are very limited.

Flatten Array

Take a nested list and return a single list with all values except nil/null.

Conway's Game of Life

Implement Conway's Game of Life.

Grep

Search a file for lines matching a regular expression pattern. Return the line number and contents of each matching line.

Knapsack

Given a knapsack that can only carry a certain weight, determine which items to put in the knapsack in order to maximize their combined value.

Ledger

Refactor a ledger printer.

Matching Brackets

Make sure the brackets and braces all match.

Nucleotide Count

Given a DNA string, compute how many times each nucleotide occurs in the string.

Pascal's Triangle

Compute Pascal's triangle up to a given number of rows.

Phone Number

Clean up user-entered phone numbers so that they can be sent SMS messages.

Pig Latin

Implement a program that translates from English to Pig Latin.

Prime Factors

Compute the prime factors of a given natural number.

Relative Distance

Given a family tree, calculate the degree of separation.

Robot Name

Manage robot factory settings.

Run-Length Encoding

Implement run-length encoding and decoding.

Series

Given a string of digits, output all the contiguous substrings of length `n` in that string.

Square Root

Given a natural radicand, return its square root.

Word Count

Given a phrase, count the occurrences of each word in that phrase.

State Of Tic Tac Toe

Determine the game state of a match of Tic-Tac-Toe.

Affine Cipher

Create an implementation of the Affine cipher, an ancient encryption algorithm from the Middle East.

All Your Base

Convert a number, represented as a sequence of digits in one base, to any other base.

Alphametics

Given an alphametics puzzle, find the correct solution.

Baffling Birthdays

Estimate the birthday paradox's probabilities.

Bank Account

Simulate a bank account supporting opening/closing, withdraws, and deposits of money. Watch out for concurrent transactions!

Binary Search

Implement a binary search algorithm.

Bottle Song

Produce the lyrics to the popular children's repetitive song: Ten Green Bottles.

Bowling

Score a bowling game.

Change the data format for scoring a game to more easily add other languages.

Flower Field

Mark all the flowers in a garden.

Food Chain

Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.

Grade School

Given students' names along with the grade that they are in, create a roster for the school.

House

Output the nursery rhyme 'This is the House that Jack Built'.

Intergalactic Transmission

Add parity bits to a message for transmission

Linked List

Implement a doubly linked list.

Parallel Letter Frequency

Count the frequency of letters in texts using parallel computation.

Piecing It Together

Fill in missing jigsaw puzzle details from partial data

Queen Attack

Given the position of two queens on a chess board, indicate whether or not they are positioned so that they can attack each other.

Rail Fence Cipher

Implement encoding and decoding for the rail fence cipher.

REST API

Implement a RESTful API for tracking IOUs.

Robot Simulator

Write a robot simulator.

Roman Numerals

Convert modern Arabic numbers into Roman numerals.

Spiral Matrix

Given the size, return a square matrix of numbers in spiral order.

Tournament

Tally the results of a small football competition.

Transpose

Take input text and output it transposed.

Wordy

Parse and evaluate simple math word problems returning the answer as an integer.

Anagram

Given a word and a list of possible anagrams, select the correct sublist.

Binary Search Tree

Insert and search for numbers in a binary tree.

Clock

Implement a clock that handles times without dates.

Crypto Square

Implement the classic method for composing secret messages called a square code.

Dominoes

Make a chain of dominoes.

Go Counting

Count the scored points on a Go board.

Markdown

Refactor a Markdown parser.

Meetup

Calculate the date of meetups.

Poker

Pick the best hand(s) from a list of poker hands.

SGF Parsing

Parsing a Smart Game Format string.

Simple Linked List

Write a simple linked list implementation that uses Elements and a List.

Sublist

Write a function to determine if a list is a sublist of another list.

Tree Building

Refactor a tree building algorithm.

Two Bucket

Given two buckets of different size, demonstrate how to measure an exact number of liters.

Word Search

Create a program to solve a word search puzzle.

Zebra Puzzle

Solve the zebra puzzle.

Zipper

Creating a zipper for a binary tree.

Book Store

To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts of multiple-book purchases.

Change

Correctly determine change to be given using the least number of coins.

Circular Buffer

A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.

Complex Numbers

Implement complex numbers.

Connect

Compute the result for a game of Hex / Polygon.

Hangman

Implement the logic of the hangman game using functional reactive programming.

List Ops

Implement basic list operations.

Mazy Mice

Meet Mickey and Minerva, two clever mice who love to navigate their way through a maze to find cheese. They enjoy a good challenge, but with only their tiny mouse brains, they prefer if there is only one correct path to the cheese.