Garbage collection overview in Java - Mini Project: Build & Apply

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Garbage Collection Overview in Java

📖 Scenario: You are managing a simple Java program that creates objects representing books in a library system. Over time, some books are no longer needed and should be cleaned up by Java's garbage collector to free memory.

🎯 Goal: Build a small Java program that creates a dictionary (HashMap) of books with their IDs, then removes some entries, and finally prints the remaining books to observe how unused objects can be discarded.

📋 What You'll Learn

Create a HashMap called books with these exact entries: 1: "Java Basics", 2: "Data Structures", 3: "Algorithms"

Create an integer variable called removeId and set it to 2

Remove the book with the key removeId from the books HashMap

Print the books HashMap to show the remaining entries

💡 Why This Matters

🌍 Real World

Managing collections of objects like books, users, or products in software applications often requires adding, removing, and cleaning up data efficiently.

💼 Career

Understanding how to manage data collections and how garbage collection works is essential for Java developers to write efficient and memory-safe applications.

1

Create the initial books HashMap

Create a HashMap called books with these exact entries: 1: "Java Basics", 2: "Data Structures", 3: "Algorithms"

Java

// Your code here

💡 Need a hint?

Use HashMap books = new HashMap<>(); and books.put(key, value); to add entries.

2

Add a variable to select which book to remove

Create an integer variable called removeId and set it to 2

Java

import java.util.HashMap;

public class GarbageCollectionDemo {
    public static void main(String[] args) {
        HashMap books = new HashMap();
        books.put(1, "Java Basics");
        books.put(2, "Data Structures");
        books.put(3, "Algorithms");
        // Your code here
    }
}

💡 Need a hint?

Use int removeId = 2; to create the variable.

3

Remove the selected book from the HashMap

Use the removeId variable to remove the corresponding entry from the books HashMap using books.remove(removeId);

Java

import java.util.HashMap;

public class GarbageCollectionDemo {
    public static void main(String[] args) {
        HashMap books = new HashMap();
        books.put(1, "Java Basics");
        books.put(2, "Data Structures");
        books.put(3, "Algorithms");
        int removeId = 2;
        // Remove the book with key removeId
        // Your code here
    }
}

💡 Need a hint?

Use books.remove(removeId); to remove the entry.

4

Print the remaining books

Print the books HashMap using System.out.println(books); to show the remaining entries

Java

import java.util.HashMap;

public class GarbageCollectionDemo {
    public static void main(String[] args) {
        HashMap books = new HashMap();
        books.put(1, "Java Basics");
        books.put(2, "Data Structures");
        books.put(3, "Algorithms");
        int removeId = 2;
        books.remove(removeId);
        // Print the books HashMap
        // Your code here
    }
}

💡 Need a hint?

Use System.out.println(books); to print the HashMap.