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Inheritance

extends - child class inherits from parent

Inheritance

Inheritance lets you reuse code. A subclass inherits non-private parent members and can override methods.

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Deep dive

The Big Picture

Inheritance lets a class acquire fields and methods from another using extends. It models "is-a" relationships.

Subclass inherits all non-private members
Common: HttpServlet, JPanel, Exception
Java allows single inheritance only (one superclass)

Enables code reuse and polymorphic behavior.

How It Works

Creating a subclass instance runs superclass constructor first (via super()), then subclass constructor.

@Override replaces inherited method behavior
super.method() calls parent version
Method calls check runtime type (dynamic dispatch)
Fields are not polymorphic - resolved at compile time

In the Java Landscape

One of the four OOP pillars, closely tied to polymorphism.

Abstract classes provide partial implementations
final classes (String, Integer) block inheritance
Sealed classes (Java 17+) permit specific subclasses
Modern Java favors composition and interfaces
Interfaces provide multiple-inheritance of behavior

Pitfalls and Best Practices

Don't inherit just to reuse code - use composition
Liskov: subclass must work wherever parent does
Mark methods final if subclasses shouldn't override
Avoid deep hierarchies (>3 levels gets brittle)
Document protected methods - they're part of your API

#java#oop#inheritance