2.15 Code Examples & Exercises

Learning Objectives

•Design a class combining encapsulation, constructors, and both instance and class members.
•Apply method overloading to support flexible object creation.
•Trace object creation and method calls across multiple objects.

Introduction

This closing topic consolidates Chapter 2: designing a class with encapsulated fields, instance and class variables, overloaded constructors, and instance/class methods working together as a complete, well-designed object.

Key Concepts

A well-designed class keeps fields private, exposes behavior through methods, and uses static members only where state is genuinely shared.

Overloaded constructors give callers flexibility without duplicating logic (chain with `this(...)`).

Code Examples

This class combines a static counter, two overloaded constructors chained with `this(...)`, private fields with validating getters/setters, and a static accessor for the shared count.

Common Mistakes

⚠Mixing instance and static members without a clear reason — decide deliberately which state belongs to the object vs. the class.
⚠Skipping encapsulation "just for this one class" — inconsistency undermines the benefits chapter-wide.

Practice

Practice 1

Programming Exercisehard

Add a `resetGrade()` instance method to Student that sets grade back to 0, and a static method `averageMaxGrade()`... actually, simpler: add an instance method `isPassing()` that returns true if grade >= 70.

Summary

Chapter 2's ideas — classes, objects, encapsulation, constructors, instance/class members, and overloading — combine into complete, well-designed classes, as shown below.

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