JVM has divided memory space between two parts one is Stack and another one is Heap space. Stack space is mainly used for storing order of method execution and local variables.
Stack always stored blocks in LIFO order whereas heap memory used dynamic allocation for allocating and deallocating memory blocks.
Memory allocated to the heap lives until one of the following events occurs :
- Program terminated
- Memory free
In contrast, the memory allocated to stack lives until the function returns. Below are the differences.
| Sr. No. | Key | Stack | Heap Memory |
|---|---|---|---|
| 1 | Basic | Stack memory is used to store items which have a very short life like local variables, a reference variable of objects | Heap memory is allocated to store objects and JRE classes. |
| 2 | Ordering | The stack is always reserved in a LIFO (last in first out) order | Heap memory is dynamic allocation there is no fixed pattern for allocating and deallocating blocks in memory |
| 3 | Size | We can increase stack memory size by using JVM parameter -XSS | We can increase or decrease heap memory size by using JVM option -Xms and -Xmx |
| 4 | Visibility | Variables are visible to only to owner thread | It is visible to all threads |
| 5 | Exception | JVM will throw java.lang.StackOverFlowError | JVM will throw java.lang.OutOfMemoryError |