class
- Java course
- Intermediate
- Lesson 1/116
- 5 min
Learn to define classes with class.
Defining a class
A class is a template used to create objects. In Java a class starts with the class keyword, followed by the class name and a body in curly braces.
Example: class User {}. Here User is the class name; the space between the braces is the body. The class name should start with an uppercase letter; for example User, Book, Order. Defining a class does not run it; it only prepares the template.
Body and fields
The class body is the area between the curly braces. You add fields and methods here. A field holds the class data; a method defines behavior.
Example: class Book { String title; }. Here title is a field of type String. Each field is declared with a type and a name, followed by a semicolon. The body can be empty but usually holds at least one field or method.
Practice Define the User class
Define a class named User. Add a String name field inside it. Write a main method; inside it create a User instance, assign a value to name and print it with System.out.println.
Starter code
// Define the User class
// Add a String name field
// Instantiate and print in mainSample solution
class User {
String name;
public static void main(String[] args) {
User u = new User();
u.name = "Alex";
System.out.println(u.name);
}
}Expected output
Alex
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is a valid Java class definition?
- def User: pass
- function User() { }
- User class { }
- class User { } Correct answer
Explanation: The class keyword, the class name and curly braces form the body.
2 Complete the class definition
class User____
String name;
}class User{
String name;
}Explanation: The curly brace starts the body.
3 Match the parts of a class
| Term | Meaning |
|---|---|
class |
Keyword |
User |
Class name |
{ } |
Body |