Using Objects

Ethan Taylor
4 min read
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Study Guide Overview
This study guide covers Unit 2: Using Objects in AP Computer Science A, focusing on object-oriented programming (OOP) concepts. Key topics include: creating and initializing objects using constructors, writing and calling methods, using the String and Math classes, and understanding reference types. This unit introduces fundamental OOP principles like abstraction and lays the groundwork for later units covering encapsulation, inheritance, and polymorphism.
#AP Computer Science A: Objects - The Night Before 🚀
Hey there! Let's get you feeling super confident for tomorrow's AP Computer Science A exam. This guide is designed to be your quick, high-impact review, focusing on the most important stuff about objects. Let's dive in!
#Unit 2: Using Objects - Overview
#Exam Weighting
- This unit is worth 5-7.5% of the exam. Expect around 2-3 multiple-choice questions.
#Enduring Understanding
Java is an object-oriented programming (OOP) language. Objects are the core of OOP, and this unit introduces them. Key OOP principles include:
- Abstraction (partly here, more in Unit 5)
- Encapsulation (Unit 5)
- Inheritance and Polymorphism (Unit 9)
#Building Computational Thinking
- You'll learn to write your first methods (like functions), which perform specific tasks.
- You'll use methods from the Math and String classes.
- You'll understand objects as reference types that represent real-world items and situations.
#Main Ideas
- Creating/Initializing Objects
- Writing/Calling Methods
- String Class & Methods
- Wrapper Classes
- Math Class
These are the building blocks for future units! 🧱
#2.1: Objects: Instances of Classes
- Objects are reference types, meaning they store a memory location rather than the actual value.
- A class is a blueprint or template for creating objects. Think of a class as a cookie cutter and an object as the cookie.
- An object is a specific instance of a class.
- Classes define the characteristics (data) and behaviors (methods) that objects of that class will have.
#2.2: Creating and Storing Objects (Initialization)
- To create an object, you use the constructor of the class.
- The constructor is called using the
new
keyword. - Parameters passed to the constructor initialize the object's attributes.
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