If Java has garbage collection, then why does OutOfMemoryError occur? [duplicate]

Question

This is a theoretical question. I am just curios that if Java has a mechanism for garbage collection to free the memory, then why does still OutOfMemoryError occur?

I searched SO for this but could get these links

Is the garbage collector guaranteed to run before Out of Memory Error?

Garbage collection before OutOfMemoryError

These do not answer my question specifically. If Java allows memory so well by using garbage collection, then why does OutOfMemoryError occur?

Answer 1

An OutOfMemoryError can occur if none of the objects in memory is eligible for garbage collection. For example:

List<MyClass> hellos = new ArrayList<>();
for (;;) {
   hellos.add(new MyClass());
}

This creates a list and keeps adding MyClass objects to it until memory runs out. None of the objects is eligible for garbage collection because there are references to all of them.