Creating packages in Java - Try It Yourself

Creating packages

📖 Scenario: You are organizing a small Java project for a bookstore. You want to keep your code neat by using packages.

🎯 Goal: Create a package named bookstore and place a class Book inside it. Then create another class Store in the default package that uses the Book class.

📋 What You'll Learn

Create a package named bookstore

Create a class Book inside the bookstore package

Add a String field title and a constructor to Book

Create a class Store in the default package

In Store, create a main method that creates a Book object

Print the book's title in the main method

💡 Why This Matters

🌍 Real World

Packages help keep Java projects organized, especially when many classes are involved. This is common in real software projects.

💼 Career

Understanding packages is essential for Java developers to write clean, maintainable, and scalable code.

1

Create the Book class inside the bookstore package

Create a package named bookstore. Inside it, create a public class called Book with a public String field named title and a constructor that takes a String parameter called title and assigns it to the field.

Java

package bookstore;

// Your code here

Hint

Start with package bookstore; at the top. Then define the class and constructor.

2

Create the Store class with a main method

Create a public class called Store in the default package. Inside it, create a public static void main(String[] args) method.

Java

// Your code here

Hint

Define the Store class and add the main method inside it.

3

Import the Book class and create a Book object

In the Store class, add an import statement for bookstore.Book. Inside the main method, create a Book object named myBook with the title "Java Basics".

Java

import bookstore.Book;

public class Store {
    public static void main(String[] args) {
        // Your code here
    }
}

Hint

Use import bookstore.Book; at the top of Store. Then create the object inside main.

4

Print the book's title

In the main method of Store, add a line to print the title of the myBook object using System.out.println.

Java

import bookstore.Book;

public class Store {
    public static void main(String[] args) {
        Book myBook = new Book("Java Basics");
        // Your code here
    }
}

Hint

Use System.out.println(myBook.title); to print the title.

Practice

1. What is the main purpose of using packages in Java?

easy

A. To group related classes and organize code

B. To execute Java programs faster

C. To create graphical user interfaces

D. To store variables globally

Solution

1. Step 1: Understand what packages do

   Packages help organize classes by grouping related ones together.

2. Step 2: Identify the correct purpose

   Grouping related classes improves code organization and readability.

3. Final Answer:

   To group related classes and organize code -> Option A

4. Quick Check:

   Packages organize code = D [OK]

Hint: Packages group classes logically for better organization [OK]

Common Mistakes:

• Thinking packages speed up program execution
• Confusing packages with GUI creation
• Assuming packages store variables globally

2. Which of the following is the correct way to declare a package named com.example.app in a Java file?

easy

A. package com_example_app;

B. Package com.example.app;

C. package com.example.app;

D. import com.example.app;

Solution

1. Step 1: Check package declaration syntax

   The package statement must be lowercase and end with a semicolon.

2. Step 2: Match the correct syntax

   package com.example.app; uses correct lowercase 'package' keyword and dot notation with semicolon.

3. Final Answer:

   package com.example.app; -> Option C

4. Quick Check:

   Correct package syntax = C [OK]

Hint: Use lowercase 'package' and end with semicolon [OK]

Common Mistakes:

• Capitalizing 'Package' keyword
• Using underscores instead of dots
• Using 'import' instead of 'package'

3. Given the following Java file content, what will be the package of the class MyClass?

package org.test.project;

public class MyClass {
    public void display() {
        System.out.println("Hello from MyClass");
    }
}

medium

A. org.test.project

B. org.test

C. project

D. default package

Solution

1. Step 1: Read the package declaration

   The first line declares the package as 'org.test.project'.

2. Step 2: Identify the package of MyClass

   Since MyClass is declared after the package statement, it belongs to 'org.test.project'.

3. Final Answer:

   org.test.project -> Option A

4. Quick Check:

   Package line matches class package = B [OK]

Hint: Class package matches the declared package line [OK]

Common Mistakes:

• Assuming partial package names
• Thinking class is in default package without declaration
• Confusing package with folder names

4. Identify the error in the following Java file related to package declaration:

package MyApp.Utilities;

public class Helper {
    // class code
}

medium

A. Missing semicolon after package statement

B. Package name should be lowercase

C. Class name should be lowercase

D. Package keyword should be capitalized

Solution

1. Step 1: Check package naming conventions

   Package names should be all lowercase letters separated by dots.

2. Step 2: Identify the error

   'MyApp.Utilities' uses uppercase letters, which is against convention.

3. Final Answer:

   Package name should be lowercase -> Option B

4. Quick Check:

   Package names lowercase = A [OK]

Hint: Package names must be lowercase letters only [OK]

Common Mistakes:

• Using uppercase letters in package names
• Forgetting semicolon after package
• Capitalizing 'package' keyword

5. You want to create a package structure for a company named "TechCorp" with a project "Inventory" and a module "Reports". Which is the best package declaration for a Java class in the Reports module?

hard

A. package techcorp_inventory_reports;

B. package TechCorp.Inventory.Reports;

C. package tech_corp.inventory.reports;

D. package techcorp.inventory.reports;

Solution

1. Step 1: Follow Java package naming conventions

   Package names should be lowercase and use dots to separate levels.

2. Step 2: Evaluate options

   package techcorp.inventory.reports; uses all lowercase and dot notation correctly. Others use uppercase or underscores incorrectly.

3. Final Answer:

   package techcorp.inventory.reports; -> Option D

4. Quick Check:

   Lowercase with dots = A [OK]

Hint: Use lowercase names separated by dots for packages [OK]

Common Mistakes:

• Using uppercase letters in package names
• Using underscores instead of dots
• Combining all names without dots