Writing Classes: every key term you need

Classes & Objects

Class: blueprint defining fields (data) and methods (functions). Object: instance of class with specific values.

Encapsulation

Hide internal details (private fields), provide controlled access (public methods). Protects data, simplifies interface.

Access Modifiers

public: accessible everywhere. private: accessible only within class. default (no modifier): accessible in package. protected: subclasses can access.

Instance Variables (Fields)

Belong to object; each instance has own copy. Declared in class; initialized in constructor or at declaration.

Class Variables (static)

Shared by all instances. Declared static. Access via ClassName.variable. Example: counter tracking total objects created.

Instance Methods

Act on object; access this (current object). Example: getName() returns object's name.

Class Methods (static)

Act on class, not instance. No access to 'this' or instance variables. Example: Math.sqrt(), Integer.parseInt().

Constructors

Initialize object; same name as class. Can have parameters. Default no-arg constructor provided if none written.

this Keyword

Refers to current object. Used to distinguish instance variables from parameters: this.name = name;

Getters & Setters

Getter: public method returning field (getName()). Setter: public method modifying field (setName(String)). Control access/validation.

Method Overloading

Multiple methods same name, different parameter types/number. Example: int add(int, int) and double add(double, double).

Unit 5 Summary

Classes combine data (fields) and behavior (methods). Encapsulation controls access. Constructors initialize; getters/setters manage data.

More AP Computer Science A guides

• Primitives
• Using Objects
• Boolean Expressions
• Loops
• Arrays