Challenges

Uppercase a String

Create a String variable inside your application and initialize it with "The quick brown fox jumps over the lazy dog". Now output this String to the terminal together with an uppercase version of the String. Check the API of the String class. String objects have a method to do just this.

Normal version: The quick brown fox jumps over the lazy dog
Uppercase version: THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG

Character Range

A character (char datatype in Java) in most programming languages is nothing but a number. The first 128 character representations are called the ASCII values (ASCII stands for American Standard Code for Information Interchange). So an ASCII code is the numerical representation of a character such as 'a' or '@'. Below is a list of these values.

ASCII Codes, source: http://www.lookuptables.com 2010

The code below requests a single character from the user. It checks if the inputted character is a lowercase alphabet letter. Expand the code so it also states if the character is a capital letter or a number. Characters can be compared just as numbers.

Take a good look at how the comparison is applied to a character datatype. Also note the difference between 1 which is the number and '1' which is the character.

Scanner console = new Scanner(System.in);

System.out.print("Please input a single character: ");
char character = console.next().charAt(0);

System.out.print("\nThe character " + character + " is a ");
if (character >= 'a' && character <= 'z') {
  System.out.println("lowercase letter");
}

Example output:

Please input a single character: 1
The character 1 is a number

Reading the Users Name

Ask the user of your application for his/her name and store this data inside a String variable. Output a personalized message.

For example:

Please supply your full name: Nico De Witte

Oh hello there Nico De Witte. Did you know that the DeLorean DMC-12, the car used in Back to the Future is a sports car manufactured by John DeLorean's DeLorean Motor Company for the American market in 1981–83?

Well I did ...

Reversing a String

Request a single word from the user and reverse it. Make sure to lowercase it first, otherwise it might look weird.

Use a basic for loop for the reversing process. Make use of the length() method to get the number of characters in the String.

For example:

Please enter a word to reverse: Banana

The word "banana" reversed is "ananab".

Palindrome

Request a single word from the user and check if it is a palindrome.

INFO - Palindrome

A palindrome is a word, number, sentence, or verse that reads the same backward or forward. It derives from the Greek palin dromo, which means "running back again"

Example output:

Please enter a word to check for palindrome: Banana

The word "banana" reversed is "ananab". This is not a palindrome.

Another example:

Please enter a word to check for palindrome: Radar

The word "radar" reversed is "radar". This is a palindrome.

Check for Character

Request a single word from the user. This can be accomplished using the next() method of Scanner.

Now creating the following String variable inside your application:

String vowels = "aeiou";

Next select a random vowel from the String. Search the word that was provided by the user and display an appropriate message to the user if the vowel was found inside the string provided by the user.

Example:

Please enter a word to search for random vowel: Banana

I picked the random vowel 'u' and did not find it in "banana".

Another example:

Please enter a word to search for random vowel: asparagus

Eureka!! I picked the random vowel 'a' and found it in "asparagus".

Search in a String

Create an application that requests a sentence from the user. Save the sentence in a String variable. Next check if the sentence contains a specific word. You can choose this word yourself. Check the String API for a method that allows you to search in a String.

For example:

Please enter sentence: The quick brown fox jumps over the lazy dog
Searching for the word "cat"
No "cat" found in "The quick brown fox jumps over the lazy dog".

Another example:

Please enter sentence: The quick brown cat jumps over the lazy dog
Searching for the word "cat"
Found the word "cat"!

Splitting a String

Create an application that requests a sentence from the user. Now split the sentence into words and print each word on a separate line. There are several ways to do this. Pick one you understand.

Example:

Please enter sentence: The quick brown fox jumps over the lazy dog

Cutting the sentence into words:
The
quick
brown
fox
jumps
over
the
lazy
dog

Secrets

Create a variable called secret of type String an initialize it with a single word (choose it yourself). Display the secret to the user but do not show the actual letters. Show some symbol instead of each letter which you can pick for yourself. Show as much symbols as that there are letters.

Now let the user guess for letters of the secret word. If the user finds a letter, display the secret again but this time with the guessed letter revealed.

You are basically creating the core of a Hangman game here.

Example:

Hello and welcome to the Secret Word game.
I have a word in mind of 5 letters. Can u guess it letter by letter?

Secret: #####

Guess a letter: y
Sorry no match.
Guess a letter: h
Nice guess!
Secret: h####
Guess a letter: p
Sorry no match.
Guess a letter: e
Nice guess!
Secret: he###
Guess a letter: l
Nice guess!
Secret: hell#
Guess a letter: o
Nice guess!
Secret: hello

Eureka!! You found my secret word.

Decimal to Hex convertor

Create a Java program that converts a decimal number (0 till 255) to hexadecimal number (0x00 to 0xFF). Only a single byte is required.

Java has no native support for hexadecimal notation so you will need to create a String for the hexadecimal number. The easiest solution lies in the usage of the the division operator / and the modulo operator %.

Example:

This program can convert decimal numbers from 0 to 255 to a hexadecimal notation.

Please input your decimal number (0 to 255): 288
Sorry, cannot convert negative numbers or numbers greater than 255.
Please input your decimal number (0 to 255): 16

The number 16 in decimal notation is represented as 0x10 in hexadecimal notation.

Thank you for using our software.

Characters can also be used in simple calculations as shown below:

char a = 'a';

System.out.println("The character after " + a + " is " + (char)(a+1) + ".");