Classes and Objects

A class groups related fields together under one named type, and a constructor is a special method, named after the class, that runs automatically whenever you create a new instance with new. this.name = name inside the constructor assigns the parameter to the object's own field, disambiguating the two when they share a name.

Main.java

Try it yourself →

public class Main {
    static class Person {
        String name;
        int age;

        Person(String name, int age) {
            this.name = name;
            this.age = age;
        }
    }

    public static void main(String[] args) {
        Person alice = new Person("Alice", 30);
        System.out.println(alice.name + " is " + alice.age + " years old");
    }
}

Output

Alice is 30 years old

Next: encapsulation — private fields, getters, and why Java code almost always hides its fields behind methods.

Practice exercise

Define a class Book with fields title (String) and pages (int). Create a Book with title "Dune" and pages 412, then print title and pages using System.out.println(book.title + " " + book.pages).

← Strings Encapsulation →