Stack memory and heap memory (Stack Vs Heap) are two crucial parts of programming that help us to ensure that our application makes efficient use of memory. We’ll talk about which information stack stores and which information heap stores and We’ll go through the difference between stack and heap also in depth in this section.
Memory management is a crucial part of every programming language. local variables, global variables, method execution orders, runtime objects, and so on can all be stored in memory.
JVM is a Java virtual machine that splits memory into two types. These two types of memory are stack memory and heap memory.
The memory allocated of the heap remains until the program finishes or the memory is freed, whereas the memory allocated of the stack remains until the function returns.
Table of Contents
Memory allocation section in Java
We all know that java contains units like bytecode, method, variable, object, static data, and static method that we use every time. Java memory allocation is divided into the four primary sections based on these units.
- Stack Section: For methods, local variables, reference variables.
- Heap Section: Objects
- Code Section: Java byte code
- Static Section: For static data and static method
What is Stack Memory in Java?
The stack is a linear data structure that follows the LIFO (Last-In-First-Out) principle. Physical memory includes the stack (RAM). The local variable, object references, and method execution order are all stored on the stack.
When we call a new method, a new block is created at the top of the stack that includes data that are specific to that method. The values might be simple variables or object references. When the execution of the method is complete, the associated block of the stack is emptied.
When we call a new method, the stack memory grows, and when that method returns anything, stack memory shrinks.
What is Heap Memory in Java?
Heap space in Java is used for dynamic memory allocation for Java objects and JRE classes at the runtime. A new object is stored in heap memory when it is created. It contains the objects that we created, as well as JRE classes.
When we create an object, object occupies memory in the heap, and a reference to that object is created in the stack. As we know garbage collection is applicable to objects that do not have a reference. As a result, garbage collection operates heap memory to free up space. When an object is generated in the heap, it becomes globally accessible and may be referenced from anywhere in the application.
When heap space is totally occupied, JVM sends the related error message (which is an error), java.lang.OutOfMemoryError.
Difference between Stack and Heap in Java
Every object we create, the heap area contains all the objects but the reference of those objects is held by the stack memory. All of the key difference between stack and heap memory (Stack Vs Heap) are listed in the table below.
| Stack Memory | Heap Memory |
|---|---|
| Stack memory stores methods calls, local variables, and reference variables of the objects. All of these objects have a short lifespan. | Heap memory stores JRE classes and objects. |
| The stack is always follow last-in-first-out (LIFO) order. | For heap memory, there is no specific pattern. |
| The size of a stack is limited by the operating system, and it is generally less than a heap. | Heap has no size restrictions. |
| Using a JVM parameter -XSS, we may raise the stack memory size. | Using the JVM parameters -Xms and -Xmx, we may raise or decrease heap memory size. |
| JVM will throw java.lang.StackOverFlowError if there isn’t enough memory on the stack to store a function call or a local variable. | JVM will throw java.lang.OutOfMemoryError: Java Heap Space, if there isn’t enough memory space to create an object. |
| In a stack, memory allocation is done in a continuous order. | In a heap, memory allocation is done in a random order. |
| Because each thread runs on its own stack, stack memory is thread safe. | Because the heap is not thread-safe, proper code synchronization is required. |
| Stack area is temporary. | As long as the application is running, heap space exists. |
When to use the Heap or Stack?
If you know exactly how much data has to be allocated before compilation, stack is the way to go. If you don’t know how much data to allocate at runtime, heap is the way to go.
When a large amount of memory is required, heap is the way to go. If you’re working with little variables, though, they’ll only be needed for the duration of the function that utilizes them. Then you should use Stack, which is more straightforward and efficient.
Is Stack faster than Heap?
Which is faster heap or stack? Yes, stack is comparatively faster than heap because the data on a stack can only be accessed by the currently running thread, and synchronization is not necessary because each thread has its own stack, which is why stack memory is faster than heap memory.
Why stack is faster than heap? As compared to heap memory, stack memory is particularly fast due to the simplicity of memory allocation (LIFO).
In conclusion, Hope you liked the article “Stack Vs Heap in Java“. If you have any doubts and queries feel free to contact us at geekcer.code@gmail.com.
FAQ
No, The heap is not thread safe and must be dealt with by properly synchronizing the code.
The stack is more safe than the heap due to the stack’s thread safety.
Allocating heaps can be expensive. It is sometimes more expensive to free than it is to allocate.
RAM memory includes all stack and heap memory. That means Heap memory is a part of RAM.
Static memory allocation is done using the stack, while dynamic memory allocation is done with the heap.
