1Z0-830 Java 21 Inheritance and Polymorphism Guide

Study 1Z0-830 Java 21 Inheritance and Polymorphism: key concepts, common traps, and exam decision cues.

This chapter is where Java design decisions become runtime dispatch and type-safety questions. The exam expects you to know what the declared type allows, what the runtime type does, and when narrowing is legal.

Work this chapter in order

Lesson	Focus
5.1 Sealed and Overrides	Learn how the exam tests abstract types, sealed hierarchies, overriding, casting, and safe narrowing.

Fast routing inside this chapter

If the question is really about…	Go first to…
abstract classes, final members, or overriding	5.1 Sealed and Overrides
sealed types and permitted subclasses	5.1 Sealed and Overrides
`instanceof`, casts, or pattern narrowing	5.1 Sealed and Overrides

What strong answers usually do

separate declared-type access from runtime-type dispatch
use sealed hierarchies as a clue for exhaustiveness and safe modeling
treat casts as legality questions first and runtime-risk questions second

In this section

1Z0-830 Java 21 Sealed Types and Overrides Guide
Study 1Z0-830 Java 21 Sealed Types and Overrides: key concepts, common traps, and exam decision cues.

Revised on Sunday, May 10, 2026

4. Objects

6. Interfaces