What are the Memory Allocations available in Java?

Bernard Aybout (Virii8)

2 years ago

Table of Contents

4 Minutes Read

Heap Memory: This is the runtime data area from which memory for all class instances and arrays is allocated. The heap is created on virtual machine start-up and may dynamically grow or shrink in size. Garbage Collection primarily occurs in this area, freeing memory by destroying objects that are no longer in use or reachable.
Stack Memory: This is where Java methods are executed. Each thread has its own stack that holds local variables and partial results, and plays a part in method invocation and return. Each method call creates a new block on the stack known as a stack frame which contains method-specific values like local variables and the return address.
Method Area: This memory area is shared among all threads and stores class-level information such as class structures, method code, and constant pools. It’s a part of the heap memory but has its own management and GC techniques.
Native Method Stack: This area is not written in Java and is reserved for native methods of the application, typically written in other languages like C or C++.
Program Counter (PC) Register: This is a small memory space that stores the address of the JVM instruction currently being executed. Each thread in Java has its own PC register.
Direct Memory (Non-Heap Memory): This is memory allocated outside of the managed heap, usually by the Java Native Interface (JNI) or by creating a direct ByteBuffer. It’s useful for large memory operations like those used in NIO channels.

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