Java Code Examples

This site lists a comprehensive collection of Java code examples categorized according to various programming concepts.

The programming concepts covered in the code examples include basic concepts, control structures, methods, arrays, classes, objects, inheritance, polymorphism, threads, file operations, data structures, sorting algorithms, mathematical functions, mathematical sequences, hashset, hashmap, exception handling, and system functions. The article provides a brief overview of the Java basics, control structures, methods, arrays, classes, objects, inheritance, polymorphism, file operations, data structures, sorting algorithms, and error handling.

In addition, it provides Java code examples with explanations and syntax for various functions such as generating random numbers, arithmetic operators, conversion programs, input/output, multidimensional arrays, dynamic and static polymorphism, and file operations like reading and writing files.

It also includes code examples for common exceptions such as ArithmeticException, ClassCastException, IndexOutOfBoundsException, and NullPointerException, and how to handle them using try-catch and throws.

Java Basics

Arithmetic operators
Bitoperators
Comments in Java
Conversion Programs
Data types in Java
Datatype String
Declaration and initialization
Escape sequences – special characters
Generate random numbers using Math.random
Generate random numbers using Random class
Generate random numbers using ThreadLocalRandom class
Hello world
Input / output
Java Code Example: check password strength
Java Code Example: convert celsius to fahrenheit
Java Code Example: convert decimal to binary number
Java Code Example: convert decimal to hexadecimal number
Java Code Example: convert decimal to octal number
Java Code Example: convert specific datatype to int
Operators in Java
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Control Structures in Java

If-else syntax
Java Code Example: advanced switch-case statement
Java Code Example: check if a number is positive or negative
Java Code Example: check leap year in if else statement
Java Code Example: christmas tree pattern
Java Code Example: double nested for-loop
Java Code Example: floyd’s triangle
Java Code Example: for loop to store even and odd items in lists
Java Code Example: hourglass pattern
Java Code Example: if else statement on boolean expressions
Java Code Example: left arrow pattern
Java Code Example: multi-branches
Java Code Example: nested for loop
Java Code Example: nested if-else statement
Java Code Example: pattern reverse
Java Code Example: right arrow pattern
Java Code Example: simple calculator
Java Code Example: simple if-else statement
Java Code Example: simple pattern
Java Code Example: triangle pattern
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Methods in Java

Call methods
Definition and declaration
Java Code Example: calculate cross sum (iterative and recursive)
Java Code Example: greatest common divisor (recursion)
Java Code Example: least common multiple
Java Code Example: passing array to method
Java Code Example: simple login
Java Code Example: tower of hanoi (recursive)
Java Code Example: volume and surface area of a ball
Java Code Example: volume and surface of a cube
Method overloading
Method parameters
Passing objects to methods
Recursion

Arrays in Java

Array syntax
Arrays.equals() – check two arrays for equality
Arrays.hashCode() – hash code of an array
binarySearch() – search array
Example 1: multidimensional array
Example 2: multidimensional array
fill() – fill array
Java Code Example: array in reverse order
Java Code Example: average of an array
Java Code Example: convert array to LinkedList
Java Code Example: Edit/compare multiple arrays
Java Code Example: even numbers in an array
Java Code Example: find pairs with target sum
Java Code Example: join two arrays
Java Code Example: largest number in an array
Java Code Example: odd numbers in an array
Java Code Example: prints out indices of all pairs of numbers
Java Code Example: searchs an array for a number
Java Code Example: smallest number in an array
Java Code Example: sum up all numbers from an array
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Classes and Objects in Java

Array of objects
Classes and objects basics
Destructor
Encapsulation via get and set methods
Java Code Example: area of ​​a rectangle
Java Code Example: create a small user management with customers and employees
Java Code Example: create items with counter
Java Code Example: data abstraction – public, private, protected
Java Code Example: volume of a cube
Static attributes and methods
The final keyword

Inheritance and Polymorphism in Java

Code Example 1: dynamic polymorphism
Code Example 1: static polymorphism
Code Example 2: dynamic polymorphism
Code Example 2: static polymorphism
Dynamic polymorphism
Hierarchical inheritance
Inheritance basics
Java Code Example: single inheritance
Java Code Example: static polymorphism (method overloading)
Multilevel inheritance
Single inheritance
Static polymorphism
The super keyword

Fileoperations in Java

Java Fileoperations: check if two files have the same content
Java Fileoperations: copy the file name and content of 10 files in another
Java Fileoperations: read the file size and type of an image
Java InputStreamReader Class
Java OutputStreamWriter Class
Line-by-line loading of a text file into a string list or string stream
Loading a binary file into an array using readAllBytes()
Loading a text file into a string using readString()
Read from file using BufferedReader
Read from file using FileReader
Write to file using BufferedWriter
Write to file using FileWriter

Data Structures in Java

Binary search tree
Linked list data structure
Queue data structure
Singly Linked List Code Example 1
Singly Linked List Code Example 2
Singly Linked List Code Example 3
Stack data structure

Sorting Algorithms in Java

Bubble sort algorithm
Counting sort algorithm
Heap sort algorithm
Insertion sort algorithm
Merge sort algorithm
Quick sort algorithm
Radix sort algorithm
Selection sort algorithm
Shell sort algorithm

Errors and Exception Handling in Java

Example: ArithmeticException (division by zero
Example: ClassCastException
Example: exception forwarding
Example: IndexOutOfBoundsException
Example: NullPointerException
Example: NumberFormatException
Example: throw new exception
Overview checked exceptions
Overview unchecked exceptions
Return exception to caller (throws keyword)
Throw new exceptions (throw keyword)
Try-catch

Lambdas in Java

Basic lambda expression
Java Code Example: consumer
Java Code Example: function
Java Code Example: predicate
Lambda Expression Use Cases
Lambda Expressions in Java: filtering even numbers
Lambda Expressions in Java: iteration, filtering, and transformation
Lambda Expressions in Java: summing numbers and finding max
Lambda Expressions in Java: transforming names to uppercase

Mathematical Functions in Java

Arithmetic sequence
Basic mathematical functions
Exponential and logarithmic math functions
Fibonacci sequence
Geometric number sequence
Incremental sequence
Mathematical rounding
Prime number sequence
Square number sequence
Triangular number sequence
Trigonometric math functions

Threads in Java

Creating threads
Java Code Example: create threads from different classes
Java Code Example: create threads via for-loop
Java Code Example: two threads communicate via shared variable
Java Code Example: waiting for thread to terminate (join)
Running threads
Thread default methods

Set / Map in Java

HashMap basics
HashSet basics
Java Code Example: advanced HashMap example
Java Code Example: advanced HashSet example
Java Code Example: advanced TreeMap example
Java Code Example: advanced TreeSet example
Java Code Example: combine HashSets
Java Code Example: convert HashSet to Array
Java Code Example: HashMap alphabet
Java Code Example: simple HashMap example
Java Code Example: simple HashSet Example
Java Code Example: simple TreeMap example
Java Code Example: simple TreeSet example
TreeMap basics
TreeSet basics

System Functions in Java

Access to properties and environment variables
Copy array via system class
Create new directory
Get system date
Show all system properties
Shutdown / restart computer