Java Inheritance and Recursion Cheat Sheet

The core ideas of Java Inheritance and Recursion distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Inheritance (extends)

A mechanism where a subclass inherits fields and methods from a superclass using the extends keyword, establishing an is-a relationship and promoting code reuse.

Method Overriding

A subclass provides its own implementation of a method inherited from the superclass. The overriding method must have the same signature (name, parameters, return type).

super Keyword

A reference to the superclass used to call the parent constructor (super()), access overridden methods (super.method()), or reference parent fields.

Polymorphism

The ability of a superclass reference variable to hold a subclass object. Method calls are resolved at runtime based on the actual object type (dynamic dispatch).

Abstract Class

A class declared with the abstract keyword that cannot be instantiated. It may contain abstract methods (no body) that subclasses must implement.

Interface

A reference type that defines a contract of method signatures that implementing classes must provide. A class can implement multiple interfaces.

Recursion

A programming technique where a method calls itself to solve a problem by breaking it into smaller instances of the same problem.

Base Case

The stopping condition in a recursive method that prevents infinite recursion. It returns a value directly without making another recursive call.

Dynamic Dispatch

The mechanism by which Java determines which overridden method to call at runtime based on the actual object type, not the reference type.

Key Terms at a Glance

Inheritance:A mechanism where a subclass acquires fields and methods from a superclass using the extends keyword.

Superclass:The parent class in an inheritance relationship. Also called the base class.

Subclass:The child class that extends a superclass, inheriting its members and optionally overriding methods.

Polymorphism:The ability to treat objects of different subclasses through a common superclass reference, with method behavior determined at runtime.

Method Overriding:A subclass providing its own implementation of a method with the same signature as one in the superclass.

Abstract Class:A class that cannot be instantiated and may contain abstract methods that subclasses must implement.

Interface:A reference type defining method signatures that implementing classes must provide. Supports multiple implementation.

Dynamic Dispatch:Runtime resolution of which overridden method to call based on the actual object type.

Recursion:A technique where a method calls itself to solve a problem by breaking it into smaller subproblems.

Base Case:The stopping condition in a recursive method that returns a value without making another recursive call.

StackOverflowError:A runtime error thrown when the call stack exceeds its size limit, typically caused by infinite recursion.

instanceof:An operator that tests whether an object is an instance of a specific class or interface.

Upcasting:Treating a subclass object as a superclass type. Always safe and implicit in Java.

Downcasting:Treating a superclass reference as a subclass type. Requires explicit cast and risks ClassCastException if the object is not actually that subclass.

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