Memory Allocation in Java: Everything You Need To Know in 2020

Memory allocation in java refers to the process where the computer programs and services are allocated dedicated to virtual memory spaces. The Java Virtual Machine divides the memory into Stack and Heap Memory. For Java Virtual Machine, executing an application in its maximum potential can happen from stack and heap memory. Every time a new variable or object is declared, the memory allocates memory dedicated to such operations. 

Stack Memory

The Stock Memory allocation in java is used for static memory and thread execution. The values contained in this memory are temporary and limited to specific methods as they keep getting referenced in Last-In-First-Out fashion.

As soon as the memory is called and a new block gets created in the stack memory, the stack memory then holds primitive values and references until the method lasts. After its ending, the block is flushed and is available for a new process to take place. In general, the overall size of the stack memory is insignificant to that of the heap memory. 

Characteristics of Stack Memory

Based on the different sections of the memory allocation in Java Virtual Machine (JVM), here are some of the discrete features of the stack memory:

  • The stack memory can grow or contract as any new methods get called and returned accordingly.
  • Any variable in the stack can run as long as the scope of the method exists.
  • It gets auto-allocation and deallocation as and when a method undergoes execution. 
  • In the case of full memory, the java.lang.StackOverFlowError sets off.
  • It is faster in access when compared to the heap memory.

Read: Full-Stack vs. Software Engineer: Which One Should You Choose?

Methods used in the stack memory allocation in java

  • Object push(Object element): Here, an item gets pushed to the top of the stack.
  • Object pop(): Any element located at the top of the stack gets flushed and returned. In case of a stack being vacant as the pop() gets invoked, the exception – EmptyStackException occurs. 
  • Object peek(): Here, the top element gets returned but doesn’t undergo flushing.
  • Boolean empty(): If the loop doesn’t have any top value in its stack, the function returns 1 (true), otherwise 0 (false).
  • In search(Object element): This is used to understand if an object is present in the stack. In case the value is found, the function returns the location of the element from the top of the stack, otherwise returns -1.

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Java Heap Space

Mainly used by java runtime, Java Heap Space comes into play every time an object is created and allocated in it. The discrete function, like Garbage Collection, keeps flushing the memory used by the previous objects that hold no reference. For an object created in the Heap Space can have free access across the application. 

The Memory allocation in java is divided into parts, namely Heap, Stack, Code, and Static.

Characteristics of the Java Heap Memory

  • Accessible from the complicated memory management technique, including the Young Generation, Old or Tenured Generation, and Permanent Generation.
  • In heap memory, when it gets full, it returns java.lang.OutOfMemoryError.
  • The access in this memory is comparatively slower than that of the stack memory.
  • It doesn’t undergo automatic deallocation and requires a similar function like Garbage Collector to remove foreign objects for the memory to work in its optimal stage.

An example of the stack and heap memory allocation in java is: 

Source

Heap Space and Stack Memory: Fundamental Differences

Heap Space Memory Stack Memory
All parts of the application invoke the heap memory. The stack memory execution is limited to a single thread.
Anytime an object gets created, it is stored in the heap space.    The stack memory only comprises its reference and local primitive variables. 
Objects here are accessible globally across the application.  Other threads cannot access stack memory objects.
Here, memory is defined according to young and old generations. Memory management occurs on a Last-In-First-Out basis.
The memory remains as per the scope of the application. Memory is temporary.
The methods like – XMX and XMS JVM are used to define the optimal size of the heap memory.  For stack memory, it gets determined by the -XSS method.
Here, the exception of java.lang.OutOfMemoryError occurs in the case of full memory. Here, the error java.lang.StackOverFlowError happens in case the memory is full.
The size is more but takes time to process compared to the stack memory.                   The size is lesser but faster in execution for its smooth LIFO operation.

Also read: Java Developer Salary in India

Conclusion

Memory allocation in java occurs in two ways, mainly, stack and heap space. We hope it helped you in understanding the process of it all.

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