Java Fundamentals

Objects

• In Java, an object represents an instance of a class.
• Objects have state (data) and behavior (methods).
• Objects can be created using the new keyword.
• Objects can be manipulated using methods.

Inheritance

• Inheritance is a mechanism in which one class can inherit the properties of another class.
• The child class inherits the properties of the parent class.
• Uses the extends keyword.
• Example: class Dog extends Animal

Polymorphism

• Polymorphism is the ability of an object to take on multiple forms.
• Method overriding: when a subclass provides a different implementation of a method already defined in its superclass.
• Method overloading: when multiple methods with the same name can be defined, differing in parameters.

Collections

• A collection is a group of objects.
• Java provides several types of collections:
  • List: an ordered collection of elements (e.g., ArrayList).
  • Set: an unordered collection of unique elements (e.g., HashSet).
  • Map: a collection of key-value pairs (e.g., HashMap).

Threads

• A thread is a separate flow of execution within a program.
• Threads can run concurrently, improving program responsiveness and performance.
• Java provides two ways to create threads:
  • Extending the Thread class.
  • Implementing the Runnable interface.

Java Environment

• The Java Virtual Machine (JVM) is the runtime environment for Java.
• The JVM provides platform independence, allowing Java code to run on any platform supporting a JVM.
• The JDK (Java Development Kit) provides tools for developing, testing, and running Java programs.

History

• Java was first released in 1995 by Sun Microsystems (now owned by Oracle Corporation).
• Java was originally designed for interactive television, but it became popular for web development.
• Java has evolved through several versions, with new features and improvements.

Applets

• An applet is a small program that runs in a web browser.
• Applets are used to add interactive content to web pages.
• Applets are deprecated since Java 9, replaced by JavaFX for rich client applications.

Exception Handling

• An exception is an event that occurs during the execution of a program, disrupting the normal flow.
• Java provides try-catch blocks to handle exceptions:
  • Try block: code that might throw an exception.
  • Catch block: code that handles the exception.
  • Finally block: code that is always executed, regardless of whether an exception was thrown.