Packages

1 Learn

A package is a folder-like group of related classes, e.g. college.library. It avoids name clashes and keeps projects tidy.

The package statement is the first line of a file. Use import to use a class from another package. java.lang (String, System) is imported automatically.

Want more detail? Open the full lesson

2 See the Code

Java

// File: college/library/Book.java
package college.library;

public class Book {
    public String title;
    public Book(String title) { this.title = title; }
}

// File: college/App.java
package college;

import college.library.Book;
import java.util.ArrayList;

public class App {
    public static void main(String[] args) {
        ArrayList<Book> list = new ArrayList<>();
        list.add(new Book("Code Garden"));
        System.out.println(list.get(0).title);
    }
}

Book lives in package college.library.
import college.library.Book lets App use Book by its short name.
ArrayList comes from the built-in package java.util.

Output

Code Garden

3 Practice

Plan a package structure for a college app: which packages would you create for students, fees and exams?

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. Where does the package statement go?
2. Which package is imported automatically?

Step 5

Answer and check the Quick Check above to unlock this.

Day 26