Lære Heap Memory: Where Objects Live

Heap memory in Java

Heap memory is a special area of memory in Java where all objects are stored while your program runs. When you create a new object using the new keyword, Java automatically places it in the heap. This part of memory is managed by the Java Virtual Machine (JVM), which takes care of allocating space for new objects and cleaning up objects that are no longer needed.

You do not need to manage heap memory directly—Java's garbage collector automatically frees up memory by removing objects that are no longer in use. This makes it easier for you to focus on writing your code, without worrying about memory leaks or manual memory management.

Heap memory is shared across all threads in your program, so any object stored here can be accessed from different parts of your code. Understanding how heap memory works is important for writing efficient, reliable Java programs.

Practical Example: User Profile Objects in Heap Memory

Suppose you are building a social media application where you need to store user profiles during a session. Each profile is represented by a UserProfile object. These objects are created at runtime and stored in the heap memory, allowing you to access, modify, or remove them as needed.

Here is a runnable example that demonstrates how objects are created on the heap, referenced, and eventually become eligible for garbage collection when no longer needed:

Main.java


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package com.example;

public class HeapMemoryDemo {
    static class UserProfile {
        String username;
        int age;

        UserProfile(String username, int age) {
            this.username = username;
            this.age = age;
        }

        @Override
        public String toString() {
            return "UserProfile{" +
                    "username='" + username + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

    public static void main(String[] args) {
        // Creating user profile objects; these live on the heap
        UserProfile user1 = new UserProfile("alice", 30);
        UserProfile user2 = new UserProfile("bob", 25);

        // Accessing objects
        System.out.println("User 1: " + user1);
        System.out.println("User 2: " + user2);

        // Removing reference to user2 object
        user2 = null;
        // At this point, user2's object becomes eligible for garbage collection

        // Creating another user
        UserProfile user3 = new UserProfile("carol", 28);
        System.out.println("User 3: " + user3);
    }
}

Key points:

Objects like UserProfile are created on the heap memory at runtime;
References (such as user1, user2, user3) point to these objects in the heap;
When a reference is set to null, the object becomes eligible for garbage collection;
Heap memory enables dynamic object creation, sharing, and management throughout your application's lifecycle.

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