Object-Oriented Programming Basics

Objects

• An object has a unique identity, state, and behaviors.
• The state of an object consists of a set of data fields (also known as properties) with their current values.
• The behavior of an object is defined by a set of methods.

Classes and Objects

• A class is a template that defines the properties and behavior of an object.
• Multiple objects can be created from a single class.
• Each object has its own state (data fields with values) but shares the same behavior (methods) as other objects of the same class.

Example: Person Class

• A Person class has a data field called name and a method called getName.
• Multiple objects can be created from the Person class, each with its own name value (e.g., O1 with name "Ahmad", O2 with name "Zaki", etc.).

Characteristics of Objects

• An object represents a real-world entity that can be distinctly identified (e.g., a student, a desk, a circle, a button, a loan).
• An object has both a state (data fields with values) and behavior (methods).

Garbage Collection

• When an object is no longer referenced, it is considered garbage.
• The JVM automatically collects garbage.

Assigning null to a Reference Variable

• If an object is no longer needed, you can explicitly assign null to a reference variable for the object.
• This helps in garbage collection.

Variables of Primitive Data Types and Object Types

• Primitive type variables hold values (e.g., int i = 1).
• Object type variables hold references to objects (e.g., Circle c = new Circle()).
• Reference variables hold the memory address of an object.

Copying Variables of Primitive Data Types and Object Types

• Primitive type assignment (e.g., i = j) copies the value.
• Object type assignment (e.g., c1 = c2) copies the reference, not the object.
• After object type assignment, both variables point to the same object.

Garbage Collection Example

• After the assignment statement c1 = c2, the object previously referenced by c1 is no longer referenced and becomes garbage.

Garbage Collection

• When an object is no longer referenced, it is considered garbage.
• The JVM automatically collects garbage.

Assigning null to a Reference Variable

• If an object is no longer needed, you can explicitly assign null to a reference variable for the object.
• This helps in garbage collection.

Variables of Primitive Data Types and Object Types

• Primitive type variables hold values (e.g., int i = 1).
• Object type variables hold references to objects (e.g., Circle c = new Circle()).
• Reference variables hold the memory address of an object.

Copying Variables of Primitive Data Types and Object Types

• Primitive type assignment (e.g., i = j) copies the value.
• Object type assignment (e.g., c1 = c2) copies the reference, not the object.
• After object type assignment, both variables point to the same object.

Garbage Collection Example

• After the assignment statement c1 = c2, the object previously referenced by c1 is no longer referenced and becomes garbage.

Learn about the fundamentals of object-oriented programming, including objects, classes, state, and behavior. Understand how classes define properties and behavior, and how multiple objects can be created from a single class.