Class: Class is a blueprint for creating objects that contain data members and member functions defined by the user.
Example: A car blueprint is created, and based on that blueprint different models of cars are made.
Object: An object is an instance of a class. It represents a person, place, or any item.
Encapsulation: Encapsulation is the method of bundling everything required to perform a task into a capsule and presenting that capsule to the user. It hides unwanted information and only shows the necessary details.
Polymorphism: Polymorphism means having many forms. There are two types: compile-time polymorphism and runtime polymorphism.
- Compile-time polymorphism: Also known as static polymorphism where the binding of the call and its code is done at compile time.
- Method Overloading: A technique that allows more than one function with the same name but different functionalities.
- Runtime polymorphism: Also called dynamic Polymorphism, where the actual implementation of the function is done during runtime.
- Method Overriding: When a child class has the same function as the parent class.
Inheritance: A class is derived from another class, using its data and implementation. The derived class is called the child class, and the child class it is the derived parent class. The main purpose of inheritance is code reusability.
- Single Inheritance: A child class is derived from the base class (A<—-B).
- Multiversal Inheritance: A child class is derived from a class that is also derived from another base class (A<—B<—C).
- Hierarchical Inheritance: When two or more classes inherit from a single class (B—>A<—C).
- Multiple Inheritance: A child class is derived from multiple base classes (A<—C—>B).Note: Multiple Inheritance is not supported in Java to prevent ambiguity.
Abstraction: Abstraction involves showing only the necessary information and hiding irrelevant details from the user.
Example: You need to know how to drive a car, not how the wires are connected inside it.A
A class does not consume any memory. It is merely a blueprint based on which objects are created.
is it always necessary to create objects from class?
Creating objects from a class is necessary if you need to use non-static methods or access non-static data members. Non-static methods and variables belong to the instance of the class, so you need to create an object to use them.
However, if a class only contains static methods or static variables, you do not need to create an object to access these members. Static methods and variables belong to the class itself, not to any specific instance.
Constructors: A constructor is a special method used to initialize objects of a class. it is called automatically when the object is created and its name is the same as the class name.
- Default constructors: A constructor that does not take any argument.
- Parameterized Constructors: Constructors that take arguments are known as parameterized constructors.
- Copy constructor: A constructor that Initializes an object using another object of the same class.
Destructor: A destructor frees up the memory pad occupied by an object. It is automatically called when an object is destroyed.
Inheritance Real-time Examples: A car, truck, and bus are different in their behavior. But share common elements like steering wheel, brakes, etc. They inherit these features.
Interface: An interface is a special type of class that contains methods wihotnot their definition. Only the declaration of methods is allowed inside the interface.
Abstract Class: An abstract class contains abstract methods, Abstract methods which are not implemented but only declared. When a subclass inherits the abstract class it needs to implement these methods.
Difference between Abstract Class and Interface:
- An abstract class have some methods can be implemented and others are left abstract.
- All methods in an interface are by abstract and must be implemented by any class that implements the interface.
Access Specifiers: Acess Specifiers are a keywords that define the accessiblility of entities like classes, and methods.
- Private: Accessible within the class in which they are declared private.
- Protected: Accessible within the same package or subclasses in different packages.
- Public: Accessible from everywhere.
Exception: An exception is an event that disrupts the normal flow of the program such as user input error or hardware failure.
Exception handling: The exceptions can be handled in the program and prevent the execution from Stopping.
- Try Block: Try block contains code that might throw an exception
- Catch Block: Catch block is used to handle the exception that occurs in the try block.
- Finally Block: The block contains that will run regardless of whether thrown or an exception was thrown.
Garbage collection: Refer to the mechanism of automatically handling the memory in a program by removing objects that are no longer needed.
Difference between Class and Structure:
- Stucture is saved in stack memory, whereas a class is saves in heap memory.
- Data abstraction cannot be achieved with a structure but can be with a class.
Abstract Class:
- When an abstract class is inherited the subclass is not required to supply the definition of the abstract method until the subclass actually uses it.
- Can have both abstract and hon-abstract methods.
- Can have final, non-final, static, and non-static variables.
Interface:
- When an interface is implemented the subclass is required to specify and implement the interface’s methods.
- Has only abstract methods.
- Has only static and final variables.
