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Programming Languages and Techniques II

1.1 Classes, Objects, and Encapsulation

3 min readLast Updated on August 9, 2024

Object-oriented programming forms the backbone of modern software development. Classes and objects are fundamental concepts, allowing developers to create structured, reusable code that models real-world entities and their interactions.

This section explores the core principles of classes, objects, and encapsulation. We'll learn how to define classes, create objects, and use access modifiers to control data visibility, setting the stage for building robust, maintainable software systems.

Class Definition and Objects

Understanding Classes and Objects

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  • Classes serve as blueprints for creating objects, defining their structure and behavior
  • Objects represent specific instances of a class, embodying its attributes and functionalities
  • Instance variables store the unique data for each object, representing its state
  • Constructors initialize new objects, setting initial values for instance variables
  • Classes encapsulate related data and methods into a single unit, promoting organization
  • Objects interact with each other through method calls, facilitating complex program behavior

Creating and Using Objects

  • Objects are instantiated using the
    new
    keyword followed by a constructor call
  • Multiple objects can be created from the same class, each with its own set of instance variables
  • Objects maintain their own state independently of other objects of the same class
  • Instance variables are accessed and modified through object references
  • Objects can be passed as arguments to methods, allowing for flexible program design
  • The
    this
    keyword refers to the current object instance within a class

Class Components and Structure

  • Classes typically contain fields (instance variables), methods, and constructors
  • Instance variables define the attributes or properties of objects created from the class
  • Methods define the behavior or actions that objects of the class can perform
  • Constructors initialize new objects, often accepting parameters to set initial values
  • Classes can include static members shared across all instances of the class
  • Inner classes can be defined within other classes, providing encapsulation and organization

Encapsulation and Data Access

Principles of Encapsulation

  • Encapsulation bundles data and methods that operate on that data within a single unit
  • Protects internal implementation details from external interference or misuse
  • Promotes data hiding, restricting direct access to an object's internal state
  • Enhances code maintainability by localizing changes to a specific class
  • Allows for better control over data access and modification
  • Facilitates abstraction by presenting a simplified interface to interact with objects

Access Control and Modifiers

  • Access modifiers control the visibility and accessibility of class members
  • Public members (
    public
    ) are accessible from any other class
  • Private members (
    private
    ) are only accessible within the same class
  • Protected members (
    protected
    ) are accessible within the same package and subclasses
  • Default (package-private) members are accessible within the same package
  • Access modifiers apply to instance variables, methods, and classes
  • Proper use of access modifiers helps enforce encapsulation and information hiding

Implementing Getters and Setters

  • Getter methods retrieve the values of private instance variables
  • Setter methods modify the values of private instance variables
  • Getters and setters provide controlled access to encapsulated data
  • Allow for validation of input data before setting values
  • Enable the implementation of read-only or write-only properties
  • Facilitate future changes to internal data representation without affecting client code
  • Naming conventions: getters start with "get", setters start with "set" (getBankBalance(), setAccountName())

Method Design and Implementation

  • Methods define the behavior and operations of objects
  • Can accept parameters to receive input data
  • May return values to provide results of their operations
  • Can be overloaded, allowing multiple methods with the same name but different parameter lists
  • Static methods belong to the class rather than instances and can be called without creating objects
  • Instance methods operate on object-specific data and are called on object references
  • Methods can invoke other methods within the same class or from other objects
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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.