Java

What's inside

Lessons go from the basics to advanced topics. Read them in order, or jump to what you need.

1. 01

   Chapter 1

   Getting Started

   • 1Java IntroductionDiscover what Java is, where it is used, and how the same Java program runs on any device thanks to the JVM.
   • 2Java Get StartedInstall the JDK, write your first program in Main.java, then compile it with javac and run it with java.
   • 3Java SyntaxUnderstand the structure of a Java program line by line: the class, the main method, statements, semicolons and curly braces.
   • 4Java OutputPrint text and numbers with println() and print(), and format your output neatly with printf().
   • 5Java CommentsUse single-line, multi-line and documentation comments to explain your code and make it easier to read.
2. 02

   Chapter 2

   Variables & Data Types

   • 6Java VariablesLearn how to create variables to store data, change their values, make constants with final, and name your variables correctly.
   • 7Java Data TypesExplore Java's 8 primitive data types, their sizes and ranges, and how reference types like String are different.
   • 8Java Type CastingConvert values between primitive types: automatic widening casting, and manual narrowing casting with (type).
   • 9Java OperatorsUse arithmetic, assignment, comparison and logical operators, and avoid the classic integer division and % pitfalls.
   • 10Java StringsWork with text in Java: length, letter case, indexOf, charAt, substring, concatenation, comparing with equals(), and special characters.
   • 11Java MathUse the built-in Math class to find maximum and minimum values, square roots, powers, absolute values, rounding and random numbers.
   • 12Java BooleansStore true/false values with boolean, build boolean expressions with comparisons, and combine conditions with &&, || and !.
   • 13Java User Input (Scanner)Read text and numbers from the keyboard with the Scanner class, and avoid the classic nextInt() + nextLine() pitfall.
3. 03

   Chapter 3

   Control Flow

   • 14Java If ... ElseMake decisions in your programs with if, else and else if, logical operators, and the short-hand ternary operator.
   • 15Java SwitchChoose one of many code blocks with switch: the classic form with case and break, and the modern arrow form (Java 14+).
   • 16Java While LoopRepeat code while a condition is true with the while loop, and run it at least once with do/while.
   • 17Java For LoopRepeat code a known number of times with the for loop, nest loops inside each other, and go through arrays with for-each.
   • 18Java Break and ContinueStop a loop early with break, skip the current iteration with continue, and exit nested loops with labels.
4. 04

   Chapter 4

   Arrays & Methods

   • 19Java ArraysStore many values in one variable with arrays: create them, read and change elements, loop through them, and use Arrays.toString() and Arrays.sort().
   • 20Java Multi-Dimensional ArraysStore data in rows and columns with two-dimensional arrays, access elements with [row][column], and loop through them with nested loops.
   • 21Java MethodsCreate your own methods to organize code into reusable blocks, call them from main, and understand what static and void mean.
   • 22Java Method ParametersPass information into methods with parameters, use several parameters, and send results back with return.
   • 23Java Method OverloadingDefine several methods with the same name but different parameters, and let Java choose the right one based on the arguments.
   • 24Java ScopeUnderstand where a variable can be used: method scope, block scope, loop scope, and why each method has its own variables.
   • 25Java RecursionLearn how a method can call itself, why every recursive method needs a base case, and solve sum and factorial problems with recursion.
5. 05

   Chapter 5

   Object-Oriented Programming

   • 26Java OOPDiscover what Object-Oriented Programming is, why Java is built around it, how classes relate to objects, and the four pillars you will master in this chapter.
   • 27Java Classes and ObjectsCreate your first class, build objects from it with the new keyword, work with multiple objects, and organize your code across multiple classes.
   • 28Java Class AttributesLearn how to declare class attributes (fields), read and modify them through objects, understand their default values, and protect them with final.
   • 29Java Class MethodsDefine methods inside a class, understand the difference between static and instance methods, and call methods on objects to work with their data.
   • 30Java ConstructorsUse constructors to initialize objects: the default constructor, constructors with parameters, the this keyword, constructor overloading, and chaining with this(...).
   • 31Java ModifiersControl who can access your classes, attributes, and methods with access modifiers, and add special behavior with non-access modifiers such as static, final, and abstract.
   • 32Java EncapsulationProtect your data by making attributes private and exposing safe public getters and setters that can validate every change.
   • 33Java InheritanceReuse code by letting one class inherit attributes and methods from another with extends, call the parent with super, override methods, and block inheritance with final.
   • 34Java PolymorphismSee how one method call can behave in many ways: method overriding, upcasting, dynamic dispatch at runtime, and arrays that hold different subclasses under one supertype.
   • 35Java AbstractionHide implementation details and show only what matters, using abstract classes and abstract methods that subclasses must complete.
   • 36Java InterfacesDefine contracts with interfaces, implement them with implements, combine multiple interfaces in one class, and add default methods.
   • 37Java EnumsRepresent a fixed set of constants with enum, use enums in switch statements, loop over them with values(), and give them attributes of their own.
6. 06

   Chapter 6

   Data Structures & Advanced Java

   • 38Java ExceptionsHandle runtime errors gracefully with try, catch, and finally, catch several exception types, raise your own errors with throw, and create custom exceptions.
   • 39Java Wrapper ClassesUse primitive values as objects with wrapper classes such as Integer and Double, understand autoboxing and unboxing, and convert text to numbers with parse methods.
   • 40Java ArrayListStore a flexible number of items with ArrayList: add, access, change, and remove elements, check the size, loop through the list, and sort it.
   • 41Java LinkedListLearn how LinkedList differs from ArrayList, when to choose each one, and how to use addFirst(), addLast(), removeFirst(), and related methods.
   • 42Java HashMapStore data as key/value pairs with HashMap: add, read, update, and remove entries, check for keys, loop with keySet(), values(), and entrySet(), and count with getOrDefault().
   • 43Java HashSetKeep a collection of unique items with HashSet: add, check, and remove elements, and get rid of duplicates in your data in one step.
   • 44Java IteratorLoop through any collection with an Iterator using hasNext() and next(), and remove items safely while looping.
   • 45Java GenericsWrite flexible, type-safe code with generics: create a generic class like Box<T>, write generic methods, and restrict the allowed types with bounded type parameters.
   • 46Java Lambda ExpressionsWrite short, nameless functions with lambda expressions, use them with forEach(), removeIf(), and sort(), and store them in functional interfaces.