Factorial Program in Java: Loop, Recursion, Streams and BigInteger
Factorial in Java with a loop, recursion, streams and BigInteger, showing exactly where int (13!) and long (21!) overflow and computing 100! with BigInteger.
Fibonacci Series in Java: Loop, Recursion, Memoization, Streams and BigInteger
Five Fibonacci implementations in Java with measured call counts, a recursion-tree diagram showing why naive recursion is exponential, memoization, the long overflow at fib(93) and BigInteger.
Number Programs in Java: Reverse, Palindrome, Armstrong, Perfect and Strong Numbers
Reverse a number, palindrome, Armstrong, perfect and strong numbers in Java, each with a dry-run table, real output and the int-overflow trap in reversing.
Java Program to Check Prime Number: 5 Methods from Brute Force to Sieve
Five ways to check a prime number in Java: naive, square root, 6k+-1, Sieve of Eratosthenes and BigInteger.isProbablePrime, with measured timings and a program to print primes in a range.
Wrapper Classes in Java: Autoboxing, the Integer Cache and the Traps to Avoid
Wrapper classes in Java explained with real output: the eight wrappers, autoboxing and unboxing, the Integer cache (127 vs 128), NullPointerException on unboxing, equals traps, NaN and negative zero.
Enum in Java: Methods, Fields, EnumMap, Switch and Singleton Explained
Enum in Java explained with a runnable program: generated methods, fields and constructors, constant-specific bodies, switch and pattern matching, EnumMap and EnumSet, and the enum singleton.
Lambda Expressions in Java: Syntax, Method References, Capture and How They Compile
Lambda expressions in Java explained with a runnable program: syntax forms, target typing, the four method-reference kinds, variable capture, this, and what javac actually generates.
HashMap Internal Working in Java: Hashing, Buckets, Resize and Treeification
How java.util.HashMap works inside: hash spreading, bucket index, load factor and resize, collision handling and treeification, with a runnable program that peeks into the table and prints real output.
Java 21 Features with Examples: Virtual Threads, Record Patterns, Sequenced Collections
All 15 JEPs in JDK 21: which became final (virtual threads, record patterns, pattern matching for switch, sequenced collections, Generational ZGC, the KEM API) and which are still preview or incubator, each with a short example and real output from JDK 21, plus interview questions.
Java 17 Features with Examples: Records, Sealed Classes, Text Blocks, Switch Expressions
Everything that became final between Java 12 and Java 17, with examples and real output from JDK 17: records, sealed classes, text blocks, switch expressions, pattern matching for instanceof, helpful NullPointerException messages, the RandomGenerator API and strong encapsulation of JDK internals, plus interview questions.