Unit 3 Mastery: Class Creation Essentials

Constructor

A special block of code in OOP that initializes the instance variables of an object.

Instance Variables

Attributes that hold the state of an object.

Name Match

Rule stating that a constructor's name must match the class name.

No Return Type

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

Automatic Call

Constructors are called automatically when using the new keyword.

No-Argument Constructor

A constructor that takes no parameters and sets instance variables to default values.

Parameterized Constructor

A constructor that accepts parameters to set instance variables to specific values.

Constructor Overloading

Having more than one constructor in a class with different parameter lists.

Default Constructor Trap

If a class has any constructor, the default no-argument constructor is no longer provided by Java.

Method Header

Defines how code interacts with the method consisting of the access specifier, return type, method name, and parameter list.

Access Specifier

Determines the visibility of a method, usually public or private.

Return Type

Indicates the type of data returned by a method.

Method Name

Follows camelCase convention and describes the action of the method.

Parameter List

Variables listed in parentheses that act as local variables within the method.

Method Signature

Consists of the method name and parameter list only, excluding return type.

return Statement

Used in methods with a return type to return a value and halt method execution.

Accessor Methods

Public methods that allow controlled access to private instance variables.

Encapsulation

The principle of keeping instance variables private and exposing them via public methods.

Pass-by-Value

When parameters are passed to a method, a copy of the value is passed.

Primitives

Basic data types like int, double, etc., where a copy of the value is passed.

Objects

References to objects are passed by value, allowing modifications to the object's state.

Common Pitfall: void Constructor

Adding void to a constructor declaration makes it a method instead.

Shadowing Variables

Naming a parameter the same as an instance variable without using 'this' to differentiate.

Unreachable Code

Code placed after a return statement which can never be executed.

Header vs. Call Confusion

Confusing method header with method call syntax.

Method Call Example

Correctly calling a method without type declarations like myObject.add(5, 10).