Java, made clear.

Tutorials, fixes for common errors, and interactive tools for every level. 300 articles available.

11 free tools Java Online Compiler JSON → POJO UUID Generator

HelloJava.java

public class HelloJava {
    public static void main(String[] args) {
        var greeting = "Hello, Java!";
        System.out.println(greeting);

        // Streams, lambdas, records — covered.
        List.of("clarity", "examples", "fixes")
            .forEach(System.out::println);
    }
}

Most popular articles

ArrayList in Java: Complete Guide with Examples

en

ArrayList in Java: how to create, add, remove, iterate, convert to array, and common pitfalls. Complete guide with working code examples.

OR Operator in Java: Bitwise | vs Logical ||

en

Java OR operators explained: | (bitwise) vs || (logical short-circuit). Truth tables, short-circuit behavior, operator precedence and examples.

Java Array Length: Finding the Size of an Array

en

Get the length of a Java array with the .length property. Works for any type, multi-dimensional arrays, and comparison with String.length() and…

String Length in Java: length() Explained

en

Get the length of a String in Java with length(). UTF-16 code units, emoji handling, surrogate pairs, null safety and comparison with…

Convert String to int in Java (Integer.parseInt)

en

Convert String to int in Java with Integer.parseInt() and Integer.valueOf(). Handle NumberFormatException, whitespace, radix, null, and safer parsing patterns.

Constructors in Java: Complete Guide

en

Java constructors explained: default, no-arg, parameterized, copy, this() chaining, super(), private constructors and common pitfalls.

Convert int to String in Java

en

Convert int to String in Java with String.valueOf(), Integer.toString(), concatenation, formatted output and the difference between them.

Methods in Java: Declaration, Parameters, Return Types

en

How methods work in Java: declaration, parameters, return values, static vs instance, overloading, access modifiers and best practices.

Random Number Generator in Java (Math.random, Random, ThreadLocalRandom)

en

Generate random numbers in Java: Math.random(), Random, ThreadLocalRandom and SecureRandom. Ranges, seeding, streams, thread-safety and gotchas.

Java substring: Extract Parts of a String

en

Extract substrings in Java with String.substring(). Index rules, common pitfalls with surrogate pairs, StringIndexOutOfBoundsException, and modern alternatives.

compareTo() in Java: Ordering and Sorting

en

compareTo() in Java: contract, Comparable interface, implementing ordering on your classes, sorting, pitfalls with equals and hashCode.

Java split() Method: How to Split a String

en

Split a String in Java with String.split(regex). Escape special characters, limit parameter, performance tips and alternatives like Splitter.

The switch Statement and switch Expression in Java

en

Java switch explained: classic statement, modern switch expression, arrow syntax, yield, pattern matching, and when to pick switch over if-else.

Read a File in Java: The Modern Way

en

Read files in Java: Files.readString, Files.readAllLines, Files.lines stream, BufferedReader, encoding, large files and try-with-resources.

Java for Loop: Classic, Enhanced, and Stream Alternatives

en

Java for loop explained: classic for(int i;...), enhanced for-each, infinite loops, break/continue, and when to use streams instead.

Using Ellipsis to Accept a Variable Number of Arguments in Java

en

Java varargs (the ellipsis ...) let methods accept any number of arguments. Syntax, overloading rules, @SafeVarargs and common pitfalls explained.

Two-Dimensional Arrays in a Recursive Java Class

en

Learn how to use 2D arrays with recursive methods in Java. Classic problems like flood fill, matrix traversal, and maze solving with…

Java HTTPS Requests with Client Certificates (Two-Way Authentication)

en

Perform mutual TLS in Java using HttpClient: load a client certificate from a PKCS12 keystore, configure SSLContext, and send authenticated HTTPS requests.