lesson00

Intro to Java

In order to use JUnit & Selenium, we are going to introduce ourselves to some basic Java concepts.

Requirements

You need to have:

• Java
• Some Java IDE (For example - Eclipse)

Materials

The slides can be found here:

• Intro to Java - Types, Data Structurs & Basic Object Model
• Intro to Java - Polymorphism - Object Equality & Interfaces
• Intro to Java - Inheritance, Abstract Classes & Polymorphism
• Intro to Java - Exceptions & JUnit

How To Export Jar

You can follow the steps from here for export yourself a .jar.

There's no need to set advanced options & manifest file.

Problem 0 - A + B

This one is for you to test the grader.

In a com.hackbulgaria.qa.week1 package, create a class called ABSumImpl, that implements the following interface, called ABSum:

public interface ABSum {
  public int sum(int a, int b);
}

sum should return a + b

Problem 1 - Zero Insertion

In a com.hackbulgaria.qa.week1 package, create a class called ZeroInsertionImpl which implements the following interface:

public interface ZeroInsertion {
  public String zeroInsertion(int n);
}

The method should return a new String, that is constructed following that rules:

• If two neighboring digits are the same (like 55), insert a 0 between them (505)
• Also, if we add two neighboring digits and take their module by 10 (% 10) and the result is 0 - add 0 between them.

For example, if we have the number 116457, result will be: 10160457:

• 1 and 1 are the same, so we insert 0 between them
• 6 + 4 % 10 = 0, so we insert 0 between them.

Examples

zeroInsertion(116457) == "10160457"
zeroInsertion(55555555) == "505050505050505"
zeroInsertion(1) == "1"
zeroInsertion(6446) == "6040406"

Problem 2 - Hack Numbers

In a com.hackbulgaria.qa.week1 package, create a class called HackNumbersImpl which implements the following interface:

public interface HackNumbers {
  // checks if n is a hack number
  public boolean isHack(int n);
  // returns the next hack number, that is bigger than n
  public int nextHack(int n);
}

A hack number is an integer, that matches the following criteria:

• The number, represented in binary, is a palindrome
• The number, represented in binary, has an odd number of 1's in it

Example of hack numbers:

• 1 is 1 in binary
• 7 is 111 in binary
• 7919 is 1111011101111 in binary

Examples

isHack(1) == True
nextHack(0) == 1

isHack(21) == True
nextHack(10) == 21

isHack(8191) == True
nextHack(8031) == 8191

Problem 3 - 100 SMS

In a com.hackbulgaria.qa.week1 package, create a class called OneHundredSmsImpl which implements the following interface:

public interface OneHundredSms {
  public String numbersToMessage(int[] numbers);
  public int[] messageToNumbers(String message);
}

Before the smartphones, when you had to write some message, the keypads looked like that:

For example, on such keypad, if you want to write Java, you had to press the following sequence of numbers:

528882

Each key contains some letters from the alphabet. And by pressing that key, you rotate the letters until you get to your desired one.

It's time to implement some encode / decode functions for the old keypads!

String numbersToMessage(int[] numbers)

First, implement the function that takes a array of integers - the sequence of numbers that have been pressed. The function should return the corresponding string of the message.

There are a few special rules:

• If you press 1, the next letter is going to be capitalized
• If you press 0, this will insert a single white-space
• If you press a number and wait for a few seconds, the special breaking number -1 enters the sequence. This is the way to write different letters from only one keypad!

Few examples:

* numbersToMessage([2, -1, 2, 2, -1, 2, 2, 2]) == "abc"
* numbersToMessage([2, 2, 2, 2]) == "a"
* numbersToMessage([1, 4, 4, 4, 8, 8, 8, 6, 6, 6, 0, 3, 3, 0, 1, 7, 7, 7, 7, 7, 2, 6, 6, 3, 2])
==
"Ivo e Panda"

int[] messageToNumbers(String message)

This function takes a string - the message and returns the minimal keystrokes that you need to write that message

Few examples:

messageToNumbers("abc") == [2, -1, 2, 2, -1, 2, 2, 2]
messageToNumbers("a") == [2]
messageToNumbers("Ivo e Panda")
==
[1, 4, 4, 4, 8, 8, 6, 6, 0, 3, 3, 0, 1, 7, 2, 6, 6, 3, 2]
messageToNumbers("aabbcc") == [2, -1, 2, -1, 2, 2, -1, 2, 2, -1, 2, 2, 2, -1, 2, 2, 2]

For more information about Java, see: https://github.com/HackBulgaria/Programming101-Java

Problem 4 - Cache

You have the following interface:

public interface Cache {
    public void add(String key, Object value);
    public Object get(String key);
    public boolean hasValue(String key);
}

Make two implementations:

• MemoryCache - store the cache in variables (in-memory)
• FileCache - store the cache in a file on the file-system. The format of the file is up to you (but you can make it JSON)

Problem 5 - String Joiner

Create a class called StringJoiner which behaves like that:

Integer[] arr = {1, 2, 3};

StringJoiner j = new StringJoiner(", ", arr);
System.out.println(j.toString()); //"[1, 2, 3]"