2.1 Classes & Objects

Learning Objectives

•Distinguish a class (blueprint) from an object (instance).
•Identify the fields and methods that make up a class definition.
•Explain why multiple objects of the same class can hold different data.

Introduction

A class is a blueprint that defines the data (fields) and behavior (methods) that its objects will have. An object is a concrete instance of a class, created at runtime, with its own copy of the class's instance data. If `Student` is the class, then `ama` and `kwame` are two distinct `Student` objects, each with their own name and grade.

Key Concepts

A class groups related fields (state) and methods (behavior) under one type name.

An object is a runtime instance of a class, created with `new`.

Each object has its own copy of instance fields — changing one object's field doesn't affect another's.

Java Syntax

Code Examples

`ama` and `kwame` are two separate `Student` objects. Each has its own `name` and `grade`, independent of the other.

Common Mistakes

⚠Treating a class and an object as the same thing — a class is a type/blueprint; an object is a specific instance of it.
⚠Expecting two objects of the same class to automatically share field values — they don't unless the field is `static`.

Practice

Practice 1

True / Falseeasy

A class is created at runtime; an object is defined at compile time.

Summary

A class defines structure and behavior; an object is a specific instance of that class with its own independent state.

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