A curated collection of Core Java programs and practical examples designed to strengthen Java fundamentals, improve problem-solving skills, and support technical interview preparation.

This repository demonstrates real-world Java concepts including:

• Collections Framework
• Java 8 Stream API
• Multithreading
• Functional Interfaces
• Comparator & Comparable
• Generics
• Reflection API
• Recursion
• Data Structures
• Common coding patterns

Many developers understand Java syntax but struggle with applying concepts in practical scenarios.

This repository helps by providing:

✅ Small focused examples
✅ Interview-oriented coding problems
✅ Clean Java implementations
✅ Topic-wise organization
✅ Easy-to-understand logic

It can be used as a:

• Java revision guide
• Interview preparation resource
• Learning reference
• Mentoring support repository

DemoProgramsJava/
│── collections/
│── streams/
│── multithreading/
│── recursion/
│── generics/
│── comparator/
│── reflection/
│── datastructures/
└── README.md

In this repository all Core Java related programs are added, which are mostly tricky one.
Topics: Core java, Collection, Multi threading, Data Structure, Generics, Java8 features, Streams, Functional Interfaces, Reflection, Recursion, Comparator related interview programs. Here all related codes are places in respective packages listed below.

• API call
  • Rest API consumer
  • Whitelist api endpoints
• ci (Coding Interview)
  • Maximum Profit
  • Roman to Integer
  • Shift to Zeros to left or right in array
• Combination
  • Array of Combination (Number)
  • String Combination
• Comparator
  • Comparator Demo
  • Comparator on Multiple Fields (Java 7)
  • Comparator on Multiple Fields (Java 8)
  • HashMap Sorting
  • TreeMap reverse operations
• Conversions
• Copy
  • Deep Copy
  • Deep Copy using CLone method
  • Shallow Copy
• Data Structure
  • Searching
    • BFS (Breath First Search) Graph
    • BFS (Breath First Search) Shortest Path Graph
    • DFS (Depth First Search) Graph
  • Sorting
    • Bubble Sort
    • Insertion Sort
    • Selection Sort
  • Binary Tree Depth
  • Detect Loop in Linked List
  • Detect and Remove Loop in Linked List
  • LRU (Last Recently Used) Cache
  • Find Value in Binary Tree
  • Traverse through Weighted Graph
• Elevator program
• File
  • Remove matching files in java8
  • Rename files from directory in java8
• Finally Block
• Generics
  • Lower Bounded Wildcards
  • Unbounded Wildcards
  • Upper Bounded Wildcards
• Hash and Equals
• Image Compression
• Immutable
• Interface - Functional Interface
• Java 8 Features
  • Design pattern using java8
    • Builder Design pattern using java8
  • Advanced Optional Demo
  • Advanced Stream operations on Department
  • Functional Interfaces
  • BiConsumer
  • BiFunction
  • BiPredicate
  • Collectors utility class
  • Comparator
  • Consumer
  • Custom Collector class
  • Custom Functional Interface with default & static methods
  • Functions
  • Map Reduce
  • Method Reference
  • Optionals
  • Predicates
  • Sequential and Parallel Streams
  • Streams
  • Suppliers
• Leet code
  • Array operations
    • Average salary excluding min and max salary
    • Find duplicate elements in array
    • Find the pair of K difference
    • Find missing element from array
    • Jump by value
    • Merge 2 sorted arrays
    • Move all Zeros at end
    • Number of sub arrays multiplication less than K
    • Number of Sequential digits between given range of numbers
    • Number of paise which sum of pairs equals to K
  • Number operations
    • Number Palindrome
    • X power of N
  • String operations
    • Anagram string
    • Reverse string
• List Operations
  • Find Missing Elements from Duplicate List
  • Remove Duplicate Elements from List
• Map Operations
  • Count Chars and Print in Order as per Count
  • Iterate Maps using Java 7 and Java 8
  • Max Repetitive Letter from String
• Method Calls
  • Method Calls on Overloaded Classes with Extending
  • Integer wrapper and primitive method calls
  • Static method calls by Extending
• Numbers Operations
  • N Prime Numbers
  • Sum of Numbers
• Overriding
  • Overriding methods
  • Overriding Rules while Extending Classes
• Palindrome
  • Array of Numbers Palindrome
  • String Palindrome with Multiple Techniques
• Pattern programs
  • Christmas Tree using Stars (*)
• Permutation
  • Permutation using Recursion and Swapping
  • Permutation using Substring
• Recursion
  • Biggest in Array
  • Factorial
  • Fibonacci Series
  • Reverse String
• Reflection
  • Get Class's Public and Private Fields
  • Get Class Information
  • Get Class's Public and Private Methods
• Runtime Package
  • Garbage Collection
  • Log Monitor
  • Run Commands using Java
• Singleton Prevention
  • Restrict Singleton from Cloning
  • Restrict Singleton from Reflection
  • Restrict Singleton from Serialization
• Store SQL
  • Run SQL Script on Oracle DB
• Multi-threading
  • Blocking Queue
  • Completable Future
  • Countdown Latch
  • Cyclic Barrier
  • Hello World Printing(100 times) from 2 Different Threads
  • Java Atomic Integer
  • Join in Thread
  • Hello World Printing from 2 Different Threads
  • Producer and Consumer using Synchronized Blocks
  • Producer and Consumer using Locks
  • Return/Get Value from Thread
  • Return/Get Value from Thread using Callable Interface
  • Sum of Numbers Range using Executor Framework
  • Synchronized method test
  • Thread Groups
  • Wait and Notify