Difference Between Stack and Heap

Java or Japan Anti-Vivisection Association is a high-level object-oriented used for general purpose and cross-platform programming language. In Java, a vital role is played by memory management. It is mainly applied to computer memory and works as a form of resource management.  

In Java, memory management is managed automatically. It divides its memory into stack memory and heap memory. From the point of view of Java, they both are beneficial for different purposes and are important memory areas. 

Stack vs Heap 

The main difference between stack memory and heap memory is that the data structure of the stack is linear while the data structure of the heap is hierarchical. Allocation of stack memory is in a contiguous block. On the other hand, the allocation of heap memory is in random order. Variables of the stack cannot be resized, whereas variables of the heap can be resized. 

Stack vs Heap

The stack memory allocation takes place in the contiguous memory block. Programmers do not worry about memory to allocate stack variables and relocating them. It is called a stack memory assignment because in function call stack assignment takes place. Compiling is known when memory is to be assigned whereas the feature is called when variables assigned memory to stack.  

For global variables heap works as a buffer in which programming languages are saved. By default, in heap memory space, all globe variables are stored. This is beneficial for the allocation of dynamic memory. Only when programmers execute instructions the memory is reserved. The heap name has no relation with heap data’s structure. 

Comparison Table Between Stack and Heap 

Parameters of ComparisonStackHeap
InterpretationIn memory, it is a linear structure wherein sequentially the information is stored.In memory, there is dynamic allocation where all the data is randomly stored.
Memory allocationIn continuous blockIn random order
Speed FasterSlower
Data structureLinearNonlinear (hierarchical)
SizeFixedPossible to resize

What is Stack? 

In contemporary era computers, every thread has a region of memory that is reserved and called its stack. When the function executes, some of its local state data may add up to the top of the stack. When the function exits responsibility to reserve that data from the stacks go to it.  

The stack is often beneficial to store variables local to the functions that are currently active. Programmers prefer a stack to store variable-length local data. If a memory’s region lies on a stack of threads, then the memory is said to be the allocation on the stack, such as stack-based memory allocation.  

Stack memory mechanisms allow the memory of the system to work as temporary data storage and behave like a first-in-last-out buffer. A stack pointer is a register that is one of the vital elements of stack memory operation. The stack pointer indicates the location of current stack memory and can be adjusted automatically whenever a stack operation is carried out.  

Some of the advantages of the stack are automatic cleanup of the object, memory cannot be easily corrupted, and a big hand in allocation and deallocation of memory. While few disadvantages of the stack are minimal memory, random access is not possible, and stack overflow while creating too many objects. 

What is Heap? 

When programmers execute the instructions, then only heap memory is allocated. This kind of memory is called heap due to its availability of memory space in pile to allocate and de-allocate. This memory allocation is not safe due to its accessibility or visibility of stored data to all threads. The accessing time or processing time is quite slow in comparison to stack memory.  

Heap memory allocation can be divided into:  

  1. Young generation- In this region of memory, all new objects or data allocate the space. In case, memory is filled Garbage collection helps to store the rest of the data.  
  2. Old or tenured generation- In this region older data objects are stored which are not often use or not at all.  
  3. Permanent generation- This region consists of JVM’s metadata for the application methods and runtime classes.  

There are several pros or benefits of using heap memory, such as variables can be accessed globally, no limit on memory size, the method used in the priority queue, and it runs garbage collection. Cons or drawbacks of usage of heap memory are more time-consuming in execution, memory management is complicated, and more time-consuming to compute. 

Main Differences Between Stack and Heap 

  1. Stack is useful for static memory allocation, which means that before the program executes memory is allocated at compile time. Whereas heap is beneficial for dynamic memory allocation, which means that memory can be freed and allocated in random order.
  2. In terms of the arrangement, the order of stack is last-in-first-out, and variables on the computer memory are directly stored. While in heap memory is not managed automatically but manually.  
  3. When it comes to thread safety, stack thread has its stack, and that’s why they are thread-safe. On the flip side, the heap is not threading safe due to its requirement of proper synchronization code.  
  4. Stack memory is helpful to store function calls and local variables. But heap memory is beneficial to store objects in Java. It does not matter in code where the object is created it will always be created inside of space heap in Java.  
  5. In stacks, stored variables are visible to the owner thread, or in Java, it is a kind of private memory. On the flip side, in heap objects which is created visible to all threads or among all threads the heap memory is shared. 


So, it can be concluded that both stack and heap are memory management platform which plays a vital role in Java. They both are chief memory areas but, they have different purposes. Allocation of stack memory is in the contiguous block. But the allocation of heap memory is in random order.  

Stack memory has the accessibility of high speed but only to local variables. On the flip side, heap memory accessibility speed has slower as compared to stack but allows access to variables globally. Allocation and deallocation are done automatically in stack memory while in heap memory it is manually done by programmers. 


  1. https://arxiv.org/abs/1505.08075
  2. https://dl.acm.org/doi/abs/10.1145/1375634.1375655
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