2.9 Instance Methods

Learning Objectives

•Write instance methods that operate on an object's fields.
•Call instance methods on a specific object.
•Explain why instance methods need an object to be called.

Introduction

Instance methods define the behavior of individual objects and can read or modify that object's instance variables. Calling an instance method requires an object to call it on (`ama.display()`), since the method operates on that specific object's data.

Key Concepts

Instance methods are declared without `static` and can freely access instance variables.

Calling `object.method()` implicitly passes the object itself so the method knows which instance's data to use.

Instance methods can call other instance methods on the same object without qualification.

Java Syntax

Common Mistakes

⚠Trying to call an instance method without an object, e.g. `Student.display()` — that only works for static methods.
⚠Forgetting that each object's instance method call operates on that object's own fields, not some shared global state.

Summary

Instance methods define per-object behavior and must be called on a specific object, which they can read and modify.

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