What is the difference between Stack and Heap?

Stack and Heap are two memory areas used by the Java Virtual Machine (JVM) to store data.

Main differences:

Characteristic	Stack	Heap
Purpose	Storage of primitive data types and object references	Storage of objects
Size	Fixed for each thread	Dynamic, shared among all threads
Management	LIFO (Last-In, First-Out), managed by JVM	Garbage Collector
Speed	Faster	Slower
Thread	Belongs to a specific thread	Shared among all threads
Lifecycle	Tied to the method’s lifecycle	Determined by Reachability

Example usage:

// Primitive data type stored in Stack
int count = 10;

// Object stored in Heap
String name = new String("Java");

// Reference to the object name stored in Stack
String anotherName = name;

Stack:

• Variables of primitive types (int, boolean, float, etc.) store their values directly in the Stack.
• References to objects (e.g., name and anotherName in the example) store in the Stack the address where the object itself is located in the Heap.
• The size of the Stack is fixed for each thread. StackOverflowError occurs in case of too deep recursion or creating a large number of local variables.
• Access to data in the Stack is organized on a LIFO basis. When a method finishes execution, its data is automatically removed from the Stack.

Heap:

• All objects created with the new operator are located in the Heap.
• The Heap is a shared memory area for all threads within a JVM.
• The size of the Heap can change dynamically.
• Memory management in the Heap is automatic, handled by the garbage collector. Unused objects (those with no active references) are removed from the Heap, freeing memory. OutOfMemoryError occurs when there is not enough memory in the Heap to create new objects.