- OOP
- Inheritance
- Encapsulation
- Polymorphism
- Abstraction
- Constructor
- Object
- Interface и class
- Access modifiers such as private, default, protected and public
- Abstract class and method
- Exception and Error
OOP
OOPs in Java organizes a program around the various objects and well-defined interfaces. The OOPs Concepts in Java are abstraction, encapsulation, inheritance, and polymorphism
Inheritance
- it is possible to inherit attributes and methods from one class to another - is a mechanism in which one object acquires all the properties and behaviors of a parent object - Java does not support Multiple inheritance
Encapsulation
- By encapsulating a class's variables, other classes cannot access them, and only the methods of the class can access them - hiding the implementation of the class and separating its internal representation from the external class or interface
Polymorphism
- is the ability to apply the same methods with the same or different sets of parameters in the same class or in a group of classes connected by an inheritance relation -
Abstraction
- is the process of hiding implementation details from the user, giving the user only the functionality - the user will own the information about what the object does, not how it does it
Constructor
- All classes have constructors, whether you define them or not, because Java automatically provides a default constructor - The constructor is a method that creates a kind of "framework" for the class. Every new object of the class must conform to it
Object
- is an individual member of a class that has a particular state and behavior that is completely determined by the class - Variables are used to store the state of the object - The object is an instance of the class - Any object can have two main characteristics: state - some data that the object stores, and behavior - actions that the object can perform
Class
- A class is a template structure that allows you to describe an object, its properties (class attributes or fields) and behavior (class methods) in a program - Class can consist methods, objects and constructors. Class is a template of an object, he has a body with fields and methods
Interface
- An interface is a reference type, it is similar to a class. It is a collection of abstract methods. - A class implements an interface, thus inherits the abstract methods of the interface - There is no implementation inside the interface The interface only describes the behavior of some object - Only immutable final fields can be in the interface
Abstract class and method
- Abstract class describes some general state and behavior that future classes - descendants of the abstract class - will have. - Similar to interfaces, abstract classes can have abstract methods, an abstract method is a method without a body (without implementation), but unlike interfaces, abstract methods in abstract classes must be explicitly declared as abstract.
Access modifiers
- public, protected, default, and private. - Protected - declarations are visible within the package or all subclasses - Default - declarations are visible only within the package (package private)
This
- Keyword this is a link to the current class instance, we can use this word to call constructors, variables and object method’s
Static
- Static methods and variables are related to the class - Static methods belong to a class, not an object. You can call them without creating an instance of the class - From a static method you can access only static variables or methods
