Anatomy of a class: fields and methods

☕ Java 17 · Your First Java Class · 1/3

A class is a blueprint

An architect's plan isn't a house, but it describes everything about the house. A class works the same way: it describes what an object looks like and what it can do.

public class Movie {

    String title;
    int releaseYear;

    public String getTitle() {
        return title;
    }
}

Part	In the example	Role
class + name	class Movie	declares the blueprint; class names start with an uppercase letter
Fields	title, releaseYear	the object's data (its state)
Methods	getTitle()	the object's behavior: what it can do

Fields: the data

A field is a variable that lives inside a class. It answers the question what do we need to know about a movie? Every field has a type and a name:

public class Movie {
    String title;          // text
    String genre;
    int releaseYear;       // whole number
    double rating;         // decimal number
    boolean isAvailable;   // true or false
}

Type	Holds	Example value
String	text	"Inception", "Action"
int	whole numbers	2010
double	decimal numbers	8.5
boolean	true or false	is the movie available to stream?

These four types cover most of the data you'll store at first. More types come later in the course.

Methods: the behavior

A method is something the object can do. It has a return type, a name, optional parameters and a body:

public class Movie {
    String title;

    public String getTitle() {               // returns a String
        return title;
    }

    public int countWatchers(int month) {    // takes an int parameter
        return 10;
    }

    public void markUnavailable() {          // returns nothing
        // no value returned
    }
}

Part	Example	Meaning
Return type	String, int, void	what the method gives back; void means nothing
Name	getTitle, markUnavailable	a verb describing the action
Parameters	(int month)	input values; empty () means none
Body	{ ... }	the code that runs when the method is called

public means the method can be called from anywhere. Access modifiers get their own section later.

A class with fields and methods is a good start, but it can't run on its own yet. Next: comments, how classes map to files, and the main method.

💻 Code: Java17_Part_1_Fundamentals_Core_Syntax on GitHub

Next: comments, files and the main method →