Inheritance and Polymorphism Concepts

Inheritance

• Definition: Mechanism where a new class (subclass) derives properties and behaviors from an existing class (superclass).
• Benefits:
  • Code reusability: Reduces redundancy by allowing classes to share code.
  • Hierarchical classification: Organizes classes in a logical structure.
• Use of extends Keyword:
  • Syntax: class SubClass extends SuperClass
• Types:
  • Single Inheritance: One subclass extends one superclass.
  • Multilevel Inheritance: Chain of inheritance (A -> B -> C).
  • Hierarchical Inheritance: Multiple subclasses extend one superclass.
• Method Overriding: A subclass can provide a specific implementation for a method already defined in its superclass.

Polymorphism

• Definition: Ability of objects to take on multiple forms or behaviors.
• Types:
  • Compile-time (Method Overloading): Same method name with different parameter lists.
  • Runtime (Method Overriding): Subclass provides a specific implementation of a method declared in its superclass.
• Benefits:
  • Flexibility: Code can be written to interact with objects of different classes uniformly.
  • Extensibility: New classes can be added without altering existing code.

Encapsulation

• Definition: Bundles data (attributes) and methods (functions) that manipulate the data into a single unit (class).
• Access Modifiers:
  • private: Accessible only within the same class.
  • public: Accessible from any other class.
  • protected: Accessible within the same package or subclasses.
• Getters and Setters:
  • Getters retrieve the value of a private field.
  • Setters modify the value of a private field.

Abstraction

• Definition: Process of hiding complex implementation details and showing only essential features of an object.
• Implementation:
  • Abstract Classes: Cannot be instantiated; can include abstract (no body) and concrete methods.
  • Interfaces: A contract that defines methods to be implemented by classes.

Interfaces

• Definition: A reference type in Java that can contain only constants, method signatures, default methods, static methods, and nested types.
• Usage:
  • Declared using the interface keyword.
  • Classes implement an interface using the implements keyword.
• Multiple Inheritance: Java allows a class to implement multiple interfaces.
• Default Methods: Interfaces can have default methods with a body, providing default functionality.

String Methods

• Commonly used methods for string manipulation in Java:
  • length(): Returns the length of the string.
  • charAt(int index): Returns the character at the specified index.
  • substring(int beginIndex, int endIndex): Extracts a part of the string.
  • toUpperCase(): Converts the string to uppercase.
  • toLowerCase(): Converts the string to lowercase.
  • indexOf(String str): Returns the index of the first occurrence of the specified substring.
  • trim(): Removes leading and trailing whitespace.
  • replace(char oldChar, char newChar): Replaces occurrences of a specified character with a new character.
  • split(String regex): Splits the string into an array based on a specified delimiter.

Inheritance

• Inheritance allows creating new classes (subclasses) based on existing classes (superclasses), inheriting their properties and behaviors.
• Key benefits:
  • Code reusability: Reduces redundancy by sharing code between classes.
  • Hierarchical classification: Organizes classes in a logical structure.
• Inheritance is implemented using the extends keyword: class SubClass extends SuperClass.
• Types of Inheritance:
  • Single Inheritance: One subclass inherits from one superclass.
  • Multilevel Inheritance: A chain of inheritance, where a class inherits from another class, which inherits from another class.
  • Hierarchical Inheritance: Multiple subclasses inherit from a single superclass.
• Method Overriding: A subclass can provide its own implementation for a method already defined in its superclass.

Polymorphism

• Polymorphism allows objects to take on multiple forms or behaviors.
• Types of Polymorphism:
  • Compile-time (Method Overloading): Same method name with different parameter lists.
  • Runtime (Method Overriding): Subclass provides a specific implementation for a method declared in its superclass.
• Benefits:
  • Flexibility: Code can interact with objects of different classes uniformly.
  • Extensibility: New classes can easily integrate without significant changes to existing code.

Encapsulation

• Encapsulation bundles data (attributes) and methods (functions) that manipulate the data into a single unit (class).
• Access Modifiers:
  • private: Accessible only within the same class.
  • public: Accessible from any other class.
  • protected: Accessible within the same package or subclasses.
• Getters and Setters:
  • Getters retrieve the value of a private field.
  • Setters modify the value of a private field.

Abstraction

• Abstraction focuses on hiding complex implementation details and showing only essential features of an object.
• Implementation:
  • Abstract Classes: Cannot be instantiated directly, can include both abstract (no body) and concrete (with body) methods.
  • Interfaces: A contract that defines methods to be implemented by classes.

Interfaces

• Interfaces in Java are reference types that can contain only constants, method signatures, default methods, static methods, and nested types.
• Interface declaration: interface InterfaceName.
• Implementing an interface: class ClassName implements InterfaceName.
• Multiple Inheritance: Java allows classes to implement multiple interfaces.
• Default Methods: Interfaces can have default methods with a body, providing default functionality.

String Methods

• Commonly used methods for string manipulation in Java:
  • length(): Returns the length of the string.
  • charAt(int index): Returns the character at the specified index.
  • substring(int beginIndex, int endIndex): Extracts a part of the string.
  • toUpperCase(): Converts the string to uppercase.
  • toLowerCase(): Converts the string to lowercase.
  • indexOf(String str): Returns the index of the first occurrence of the specified substring.
  • trim(): Removes leading and trailing whitespace.
  • replace(char oldChar, char newChar): Replaces occurrences of a specified character with a new character.
  • split(String regex): Splits the string into an array based on a specified delimiter.