01.04 · Cheat sheet

OOP

The four pillars, overloading vs overriding, abstract class vs interface, access modifiers, constructors, key keywords, relationships and SOLID on one page.

3 min Cheat sheet Pro

Object-oriented programming in Java and C++, the way interviewers ask it.

The four pillars

Encapsulation: hide the data, expose methods (private fields + getters and setters).
Abstraction: show what it does, hide how (abstract classes, interfaces).
Inheritance: reuse code through an is-a link (extends).
Polymorphism: one name, many forms (overloading and overriding).

Overloading vs overriding

	Overloading	Overriding
Where	Same class	Subclass
Signature	Different parameters	Same signature
Decided at	Compile time	Run time
Return type	Can differ	Same (or a subtype)

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Inside: 9 sections.

The four pillars
Overloading vs overriding
Abstract class vs interface (Java)
Access modifiers (Java)
Constructors
Keywords
+3 more

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Item 4 of 12 · updated 2026-10-13