Java Classes and Objects

Classes and Objects

• A class is a blueprint or a template that defines the properties and behavior of an object.
• An object is an instance of a class, and it has its own set of attributes (data) and methods (functions).
• In Java, a class is defined using the class keyword, and an object is created using the new keyword.

Inheritance

• Inheritance is a mechanism in which one class can inherit the properties and behavior of another class.
• In Java, inheritance is achieved using the extends keyword.
• The child class inherits all the fields and methods of the parent class and can also add new fields and methods or override the ones inherited from the parent class.

Polymorphism

• Polymorphism is the ability of an object to take on multiple forms.
• In Java, polymorphism is achieved through method overriding and method overloading.
• Method overriding: when a subclass provides a different implementation of a method that is already defined in its superclass.
• Method overloading: when multiple methods with the same name can be defined with different parameter lists.

Encapsulation

• Encapsulation is the concept of bundling data and methods that operate on that data within a single unit (class).
• In Java, encapsulation is achieved using access modifiers (public, private, protected) to control access to the data and methods of a class.

Abstraction

• Abstraction is the concept of showing only the necessary information to the outside world while hiding the internal details.
• In Java, abstraction is achieved using abstract classes and interfaces.
• Abstract classes: cannot be instantiated and are used to provide a common base class for a group of related classes.
• Interfaces: define a contract that must be implemented by any class that implements it.

Composition

• Composition is the concept of creating objects from other objects or collections of objects.
• In Java, composition is achieved using container classes such as ArrayList, HashMap, etc.

Interface

• An interface is a abstract class that contains only constants and method signatures.
• A class that implements an interface must provide an implementation for all the methods defined in the interface.
• Interfaces are used to define a contract that must be implemented by any class that implements it.

Abstract Class

• An abstract class is a class that cannot be instantiated and is used to provide a common base class for a group of related classes.
• An abstract class can contain both abstract and non-abstract methods.
• A class that extends an abstract class must provide an implementation for all the abstract methods defined in the abstract class.

Constructor

• A constructor is a special method that is used to initialize objects when they are created.
• A constructor has the same name as the class and does not have a return type.
• In Java, a default constructor is provided by the compiler if no constructor is defined in the class.

Classes and Objects

• A class defines the properties and behavior of an object, and an object is an instance of a class with its own attributes and methods.
• In Java, a class is defined using the class keyword, and an object is created using the new keyword.

Inheritance

• Inheritance allows a class to inherit the properties and behavior of another class.
• In Java, inheritance is achieved using the extends keyword.
• The child class inherits all the fields and methods of the parent class and can also add new fields and methods or override the ones inherited from the parent class.

Polymorphism

• Polymorphism is the ability of an object to take on multiple forms.
• In Java, polymorphism is achieved through method overriding and method overloading.
• Method overriding is when a subclass provides a different implementation of a method that is already defined in its superclass.
• Method overloading is when multiple methods with the same name can be defined with different parameter lists.

Encapsulation

• Encapsulation is the concept of bundling data and methods that operate on that data within a single unit (class).
• In Java, encapsulation is achieved using access modifiers (public, private, protected) to control access to the data and methods of a class.

Abstraction

• Abstraction is the concept of showing only the necessary information to the outside world while hiding the internal details.
• In Java, abstraction is achieved using abstract classes and interfaces.
• Abstract classes cannot be instantiated and are used to provide a common base class for a group of related classes.
• Interfaces define a contract that must be implemented by any class that implements it.

Composition

• Composition is the concept of creating objects from other objects or collections of objects.
• In Java, composition is achieved using container classes such as ArrayList, HashMap, etc.

Interface

• An interface is an abstract class that contains only constants and method signatures.
• A class that implements an interface must provide an implementation for all the methods defined in the interface.
• Interfaces are used to define a contract that must be implemented by any class that implements it.

Abstract Class

• An abstract class is a class that cannot be instantiated and is used to provide a common base class for a group of related classes.
• An abstract class can contain both abstract and non-abstract methods.
• A class that extends an abstract class must provide an implementation for all the abstract methods defined in the abstract class.

Constructor

• A constructor is a special method that is used to initialize objects when they are created.
• A constructor has the same name as the class and does not have a return type.
• In Java, a default constructor is provided by the compiler if no constructor is defined in the class.