Java Console Input and Output: System.out, Console and IO
Java console input and output with System.out, System.err, printf, Scanner, Java 25 IO, the Console class, hidden passwords and the null console case.
Average of N Numbers in Java: Loop, Array, List and Streams
Calculate the average of N numbers in Java from user input, arrays and lists, and avoid integer division, overflow and empty input bugs.
Count Vowels and Consonants in a String in Java
Count vowels and consonants in Java with a loop, switch, streams and regex, plus y, digits, accents and locale pitfalls, with tested examples.
Reverse Words in a String in Java (6 Ways with Code)
Reverse words in a string in Java with split() and join, List.reversed(), a loop, streams, two pointers and StringUtils, with extra spaces and punctuation.
Sort a String Array Alphabetically in Java
Sort a String array alphabetically in Java with Arrays.sort, ignore case, reverse it, use Collator for accents, and handle null elements.
Swap Two Numbers in Java With and Without a Temp Variable
Swap two numbers in Java with a temp variable, arithmetic, XOR or one line, and learn where each trick fails and why a swap method cannot work.
Prime Numbers From 2 to N in Java (Sieve of Eratosthenes)
Find prime numbers from 2 to N in Java with the Sieve of Eratosthenes, check one number fast, get the first N primes and test big numbers.
Deficient Number in Java: Check, Deficiency and Examples
Check a deficient number in Java with a loop or the faster square-root method, compute the deficiency, and classify perfect and abundant numbers.
Pronic Number in Java: Check n(n+1) With or Without a Loop
Check a pronic number in Java with a loop, the square root or the 4x+1 test, handle long values safely, and generate the n(n+1) sequence.
Harshad Number in Java: Niven Number Check With Examples
Check a Harshad number in Java with a digit-sum loop that never divides by zero, try other bases, count Harshad numbers and build a lucky-draw rule.
Happy Number in Java: HashSet and Floyd Cycle Detection
Check a happy number in Java with a HashSet, Floyd cycle detection or the stop-at-4 shortcut, and see why every unhappy number reaches the same cycle.
Disarium Number in Java: Program, Examples and Full List
Check a disarium number in Java with exact integer math, see why 89, 135 and 518 qualify, list all 20 of them and compare them with Armstrong numbers.