In order to run on the Java Virtual Machine (JVM), every Java application requires a certain amount of memory. This memory is taken from the available RAM (Random Access Memory) of the system where the application is running.
In my previous posts, I have mentioned about two memory space which can be accessible from the links below. Before starting this post please read my posts about Heap Memory and Stack Memory to understand them more detailed.
In this post we will examine the differences between them and compare these two memory spaces.
Heap memory is dynamic memory that is allocated at runtime. It is typically used to store data that needs to be available for the lifetime of the program, such as objects and other variables that are created and destroyed dynamically. The heap is also used to allocate memory for data structures that may change size during the execution of the program, such as arrays and linked lists.
Stack memory, on the other hand, is static memory that is allocated at compile time. It is used to store local variables and function arguments. The stack is organized in a Last-In, First-Out (LIFO) fashion, with the most recently added data being the first to be removed.
Basically, by default anything with a size known at compile-time is by default stored on the stack. The heap is generally for things which can grow, shrink, or otherwise have a size unknowable at compile-time.
There are key differences between Stack memory and Heap memory.
Heap memory is slower to access than stack memory
One key difference between heap memory and stack memory is that heap memory is (not always) slower to access than stack memory. This is because the heap is not organized in a contiguous block of memory, so it takes longer to locate a specific piece of data. Stack memory, on the other hand, is organized in a contiguous block and can be accessed much more quickly.
The other thing to make Stack faster is that Stack Memory is managed and optimized by the CPU quite closely. Hence reading from and writing to stack variables is very fast.
Unlike Stack memory, Heap memory is not as tightly managed by the CPU.
Memory Size
Heap memory is generally much larger than stack memory. This is because the stack is limited by the size of the program’s call stack, while the heap can be dynamically expanded as needed . However, this also means that heap memory is more prone to fragmentation, which can lead to performance issues.
- The stack size is determined at compile time by the compiler.
- The heap size varies during runtime.
If heap space is full, Java throws “java.lang.OutOfMemoryError”. If the stack memory is filled completely, JVM throws “Java.lang.StackOverFlowError” error.
Security
Stack memory allocation is considered safer as compared to heap memory allocation because the data stored can only be accessed by the owner thread. This means that data stored on the stack is only accessible to the function that created it, and it is automatically deleted when the function returns.
Data stored in Heap Memory is available or visible to all threads, heap memory allocation is not as safe as stack memory allocation. This makes heap memory more prone to security vulnerabilities, as it can be more difficult to track and control access to the data stored there.
Overall, stack memory is generally considered to be more secure than heap memory, but both types of memory can be made more secure through careful design and implementation.
Summary
Stack memory is a linear data structure that stores items in a last-in, first-out (LIFO) manner and is managed automatically by the operating system. It is fast but has a fixed size. Heap memory is a more flexible data structure that allows for dynamic allocation and deallocation of memory and is managed by the program. It is slower but can store a larger amount of data. Stack memory is typically used for small amounts of data that are required temporarily while a program is running, while heap memory is used for larger amounts of data that are needed for longer periods of time.
Thanks for reading!