In this challenge, you will practice creating your own **class** and using it in a Java program. Your goal is to define a class named `Book` with two fields:

- A `String` called `title`;
- An `int` called `pages`.

Add a method called `printDetails` that prints the book's title and number of pages. Then, in the `main` method, create a `Book` object, set its fields, and call the `printDetails` method to display the information.

package com.example;

import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.util.regex.Pattern;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

public class MainTest {
    @Test
    @DisplayName("main() prints correct Book details")
    void testPrintsBookDetailsFlexible() {
        ByteArrayOutputStream outContent = new ByteArrayOutputStream();
        PrintStream originalOut = System.out;
        System.setOut(new PrintStream(outContent));

        com.example.Main.main(new String[]{});

        System.setOut(originalOut);

        String output = outContent.toString().trim();
        Pattern pattern = Pattern.compile("title\s*:\s*java\s*basics\s*,\s*pages\s*:\s*200", Pattern.CASE_INSENSITIVE);
        assertTrue(pattern.matcher(output).find(), "Output should contain: Title: Java Basics, Pages: 200. Actual output: " + output);
    }

    @Test
    @DisplayName("Book class exists and has required fields and method")
    void testBookStructure() throws Exception {
        Class<?> bookClass = Class.forName("com.example.Book");
        assertTrue(bookClass.getDeclaredField("title").getType().equals(String.class), "Field 'title' should be of type String");
        assertTrue(bookClass.getDeclaredField("pages").getType().equals(int.class), "Field 'pages' should be of type int");
        assertTrue(bookClass.getDeclaredMethod("printDetails").getReturnType().equals(void.class), "Method 'printDetails' should return void");
    }
}

MainTest.java

A beginner-friendly course introducing the essentials of Java programming, including syntax, data types, control flow, and foundational object-oriented concepts. Each section builds on the previous, with practical challenges to reinforce learning.

Learn the basics of Java syntax, structure, and how to write your first program.

Dive into Java's primitive data types and learn how to declare and use variables.

Master the basics of decision making and repetition in Java programs.

Discover how to write reusable code using methods in Java.

Get started with object-oriented programming by defining and using simple classes.

Challenge: Basic Class Usage

Løsning