1.6 Class and Object Definitions

Anatomy of a class

A class is a blueprint for objects. It typically contains instance variables (fields storing state/data), a constructor (initializes a new object), and methods (define behavior). Instance variables should usually be declared private to enforce encapsulation, while constructors and methods used outside the class are usually public.

Constructors

A constructor has the same name as the class, no return type, and runs when an object is created with `new`. It initializes instance variables, often using parameters. If parameter names match field names, use `this.fieldName = fieldName;` to distinguish them from local parameters.

Accessors and mutators

Accessor methods (getters) return the value of an instance variable without changing it, e.g., `public int getAge()`. Mutator methods (setters) change an instance variable's value, e.g., `public void setAge(int age)`. These methods let outside code interact with private data safely, preserving encapsulation.

Key terms

Class

A blueprint for creating objects, defining instance variables, constructors, and methods.

Constructor

A special method with the same name as the class and no return type; initializes a new object's instance variables.

Accessor method

A method (getter) that returns the value of an instance variable without changing it.

Mutator method

A method (setter) that changes the value of an instance variable.

this keyword

Refers to the current object; used to distinguish instance variables from parameters with the same name.

Try an AP-style question

What is the relationship between a class and an object?

1. They are the same thing
2. A class is a type of variable
3. An object is a blueprint; a class is an instance
4. A class is a blueprint; an object is an instance