Garbage collection in Java automatically frees up memory by removing objects that are no longer needed by your program. When you create new objects, Java stores them in a special area of memory called the heap. As your program runs, some objects become unreachable because there are no references pointing to them. The garbage collector finds these unused objects and deletes them, which helps prevent memory leaks and keeps your program running smoothly. You do not need to manually manage memory, making your code safer and easier to maintain.

Importance of Memory Management and Garbage Collection

Imagine you are building a web server that handles thousands of user requests per minute. Each request creates new objects to process user data. If you do not manage memory well, your server can run out of memory and crash, causing downtime and a poor user experience.

Java's garbage collector automatically reclaims memory from objects that are no longer in use, so you do not have to manually free memory. However, if you hold references to objects you no longer need (for example, by storing them in a global list), the garbage collector cannot reclaim that memory. This leads to a memory leak.

Example: Memory Leak in a Web Server

Suppose you have a SessionManager that keeps track of user sessions. If you forget to remove sessions that are no longer active, memory usage grows over time and eventually exhausts the heap.

package com.example;

import java.util.HashMap;
import java.util.Map;

public class SessionManager {
    private final Map<String, UserSession> sessions = new HashMap<>();

    public void createSession(String userId) {
        sessions.put(userId, new UserSession(userId));
    }

    public void endSession(String userId) {
        sessions.remove(userId);
    }

    public int getActiveSessionCount() {
        return sessions.size();
    }

    public static void main(String[] args) {
        SessionManager manager = new SessionManager();
        // Simulate user sessions
        for (int i = 0; i < 1_000_000; i++) {
            String userId = "user" + i;
            manager.createSession(userId);
            // Forgetting to call manager.endSession(userId) causes memory leak
        }
        System.out.println("Active sessions: " + manager.getActiveSessionCount());
    }
}

class UserSession {
    private final String userId;
    public UserSession(String userId) {
        this.userId = userId;
    }
}

Key takeaway:

• Always remove references to unused objects so the garbage collector can reclaim memory;
• Monitor memory usage and watch for growing collections that may cause memory leaks;
• Rely on Java's garbage collection, but understand how your code structure can prevent it from working effectively.