Mastering Object-Oriented Design in Java

Class

A programmer-defined blueprint from which objects are created, defining state and behavior.

Object

A specific instance of a class representing a real entity with a specific state.

Instance

Another term for object; involves creating an object by instantiating a class.

Encapsulation

Bundling data and methods within a class and restricting access to its inner workings.

Visibility Modifier

Keywords in Java that define how accessible a component is.

Private

Modifier that makes a variable or method visible only within its own class.

Public

Modifier that allows visibility of a class member to all other classes.

Instance Variables

Fields that store the state of an object, declared within a class but outside any method.

Default Values

Automatic values assigned by Java if instance variables are not explicitly initialized.

Constructor

A special method used to initialize a newly created object.

No-Argument Constructor

Constructor that sets fields to generic default values.

Parameterized Constructor

Constructor that accepts arguments to set instance variables to specific values.

Constructor Overloading

Having multiple constructors in a class with the same name but different parameter lists.

Accessor Method (Getter)

Public method that retrieves the value of a private instance variable.

Mutator Method (Setter)

Public method that modifies the value of a private instance variable.

Variable Scope

The region of code where a variable is accessible.

Instance Scope

Scope of variables declared in a class and accessible by all methods in that class.

Local Scope

Scope of variables declared inside a method, accessible only within that method.

this Keyword

Reference to the current object, used to resolve naming conflicts.

Variable Shadowing

When a local variable has the same name as an instance variable, overshadowing it.

Precondition

Condition that must be true before a method is called for it to operate correctly.

Postcondition

Condition that holds true after a method has completed execution.

toString Method

A method that provides a readable string representation of an object.

Static Variable

Variable belonging to the class that is shared among all instances.

Instance Variable vs. Static Variable

Instance variables have their own copy per object; static variables are shared.

Void Constructor Error

Mistake of adding 'void' to a constructor, making it a regular method instead.

Public Fields Mistake

The error of having public fields that violate encapsulation principles.

Shadowing Logic Error

Error caused by confusion due to parameter and instance variable name clashing.

Uninitialized Variables Mistake

Error from using a local variable without initializing it.

Return Type Mismatch Error

Mistake of having a method return type that does not match the returned variable type.

Mnemonic P.I.E.

A way to remember aspects of Object-Oriented design: Polymorphism, Inheritance, Encapsulation.

Class Anatomy Structure

Structure includes instance variables, constructors, and methods.

Constructor Naming Rule

The constructor name must match the class name exactly.

Constructor Return Type Rule

Constructors do not have a return type, not even 'void'.

Method Decomposition

Breaking down methods into manageable parts following pre and post conditions.

GPA Validation Logic

Make sure the new GPA is within the range of 0.0 to 4.0 before assigning.

Accessing Private Variables

Use public accessor methods to interact with private variables.

Understanding Constructors

Constructors are invoked automatically when 'new' keyword is used.

Object Instantiation

The process of creating an object based on a class.

Multiple Constructors

Using different parameter types or counts to define multiple constructors in one class.

Instance Variables Scope

Always accessible by all methods of the class in which they are declared.

Default Values for Non-Initiated Variables

Default assignment happens: int=0, double=0.0, boolean=false, objects=null.

Java's Object Class

Every class in Java is derived from the generic Object class.

Mutable Object

An object whose state can be changed after it is created.

Immutable Object

An object whose state cannot be modified after it is created.

Abstract Class

A class that cannot be instantiated and often contains abstract methods.

Interface

A contract that defines methods which implementing classes must provide.

Inheritance

A mechanism to derive a new class from an existing class, inheriting fields and methods.

Polymorphism

Allowing methods to do different things based on the object it is acting upon.