Przegląd Języka Java

Java Language Overview

• Java is a high-level, object-oriented programming language.
• Designed to have "write once, run anywhere" (WORA) portability.
• Compiled into bytecode (.class files).
• Bytecode is executed by the Java Virtual Machine (JVM) and is platform independent.
• Java is widely used in web applications, mobile apps (Android), enterprise applications, and more.
• Key features include:
  • Object-oriented programming principles (encapsulation, inheritance, polymorphism)
  • Strong typing system
  • Automatic garbage collection
  • Exception handling mechanisms
  • Rich standard library

Java Data Types

• Java uses primitive data types to represent fundamental values:
  • int: 32-bit integer
  • long: 64-bit integer
  • float: 32-bit single-precision floating-point number
  • double: 64-bit double-precision floating-point number
  • char: 16-bit Unicode character
  • boolean: true or false logical value
  • byte: 8-bit integer
  • short: 16-bit integer
• Java also has reference data types (objects).
• Objects can store complex data and methods in their respective class definitions.

Java Object-Oriented Concepts

• Classes: Blueprints for creating objects.
• Objects: Instances of classes.
• Methods: Functions associated with classes or objects.
• Variables: Data associated with classes or objects.

Variables and Data Types

• Variables store data values.
• Variable declaration syntax: dataType variableName;
  • Example: int age;
• Variable initialization: dataType variableName = value;
  • Example: int age = 30;
• Data types define the type of data a variable can hold.
• Primitive data types (e.g. int, float, boolean) directly store values.
• Reference data types (e.g. objects) store references to objects.

Control Structures

• if-else statements: Conditional execution of code.
• switch statements: Selection between multiple cases.
• for loops: Iterating over a range of values.
• while loops: Repeating a block of code as long as a condition is true.
• do-while loops: Repeating a block of code at least once, then continuing as long as a condition is true.

Java Operators

• Arithmetic operators: +, -, *, /, %.
• Comparison operators: ==, !=, >, <, >=, <=.
• Logical operators: && (AND), || (OR), ! (NOT).
• Assignment operators: =, +=, -=, *=, /=, %=

Java Input/Output (I/O)

• Java provides classes for reading input from the console and writing output to the console.
• Scanner class reads input from the user.
• System.out.println() prints output to the console.
• System.in is the standard input stream.

Exception Handling

• Java uses exceptions to handle errors that may occur during program execution.
• try-catch blocks are used to handle exceptions.
• throws keyword declares that a method might throw an exception.
• finally block is executed regardless of whether an exception occurs.

Arrays in Java

• Arrays are used to store collections of values of the same data type in a contiguous memory location.
• Declaration: dataType[] arrayName = new dataType[size]; or dataType arrayName[] = new dataType[size];
• Access elements of an array using their index.

Classes and Objects

• Creating classes:
  • Define data members (attributes/variables) and methods (behaviors).
  • Example: a Dog class with attributes like name and breed and method to bark().
• Creating objects:
  • Using the class name to create an instance of that class.
• Accessing class members (methods, attributes): using dot notation.
• Constructors: initializing objects upon their creation.

Methods

• Methods are operations that objects can perform.
• Return types (e.g., int, String) determine the data type of the value returned.
• Methods can take arguments.
• void methods don't return any value.

Inheritance and Polymorphism

• Inheritance allows classes to inherit properties and methods from other classes.
  • Enables code reusability and establishes relationships between classes.
• Polymorphism allows methods to have different behaviors depending on the object they are called upon.

Packages

• Organize Java classes into logical units and prevent naming conflicts.

Libraries and Frameworks

• Libraries provide ready-made functions and components for specific tasks.
• Frameworks offer infrastructure for building certain types of applications, like web applications.

Commonly used libraries in Java

• The Java Standard Library (e.g., java.util, java.lang) provides core functionalities.
• External libraries like Apache libraries are extensively used for projects ranging from data handling to HTTP programming.

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