What's the difference between StackOverflowError and OutOfMemoryError

Short answer:

• OutOfMemoryError is related to Heap.
• StackOverflowError is related to stack

Long answer:

When you start JVM you define how much RAM it can use for processing. JVM divides this into certain memory locations for its processing purpose, two of those are Stack & Heap

If you have large objects (or) referenced objects in memory, then you will see OutofMemoryError. If you have strong references to objects, then GC can't clean the memory space allocated for that object. When JVM tries to allocate memory for new object and not enough space available it throws OutofMemoryError because it can't allocate the required amount of memory.

How to avoid: Make sure un-necessary objects are available for GC

All your local variables and methods calls related data will be on the stack. For every method call, one stack frame will be created and local as well as method call related data will be placed inside the stack frame. Once method execution is completed, the stack frame will be removed. ONE WAY to reproduce this is, have an infinite loop for method call, you will see stackoverflow error, because stack frame will be populated with method data for every call but it won't be freed (removed).

How to avoid: Make sure method calls are ending (not in an infinite loop)

Imagine you have a function like the following

public void f(int x) {
    return f(x + 1);
}

When you'll call it the call will call f again and again and again. At each call a bit of information is stored on the stack. Since the stack is limited in size you will get a StackOverflowError.

Now imagine the following code:

for (int i = 1; i > 0; i++)
    vector.add(new BigObject());

where BigObject is a normal Java object. As you see, the loop never terminates. Each allocation is done on the heap thus it will be filled with BigObjects and you will get an OutOfMemoryError.

To recap:

• OutOfMemoryError is thrown when you are creating objects
• StackOverflowError is thrown when you are calling functions

StackOverflowError happens when you execute too many methods one inside another (for example with an infinite recursion), which is limited by the size of the stack.

OutOfMemoryError happens when the JVM runs out of space to allocate new objects, which are allocated on the heap.