2.6 Instance Variables

Learning Objectives

•Declare instance variables within a class.
•Explain how instance variables differ per object.
•Apply appropriate access modifiers to instance variables.

Introduction

Instance variables (also called fields) are declared inside a class but outside any method, and each object gets its own independent copy. They represent the state that differs from one object to another — like each Student's own `name` and `grade`.

Key Concepts

Instance variables are declared at class level, without `static`.

Each object created from the class gets its own copy of every instance variable.

Unlike local variables, instance variables get automatic default values (0, false, null, etc.) if not explicitly initialized.

Java Syntax

Common Mistakes

⚠Declaring a field `static` by mistake, which makes it shared across all objects instead of per-object.
⚠Leaving instance variables `public`, bypassing encapsulation.

Summary

Instance variables hold per-object state, declared without `static` at class level, and default automatically if not explicitly initialized.

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