Where are reference types stored and what happens to them during application runtime?

Reference types are stored in the heap.

During the application's runtime, the following occurs:

1. Creation: When creating an object of a reference type (for example, new MyClass()), memory for this object is allocated on the heap. The variable that holds it contains a reference to this memory location.
2. Access: Access to the object's fields and methods is through this reference.
3. Garbage Collection: When the object is no longer accessible from any active part of the program (no references to it), the garbage collector can free the memory it occupies on the heap. This process happens automatically "in the background" and does not require explicit developer intervention. The garbage collector periodically scans the heap, finds unreachable objects, and returns their memory to the system.
4. Modification: The contents of an object in the heap can be changed. If multiple reference variables point to the same object, changing its state through one variable will be visible through others.
5. Reassignment of reference: A reference type variable can be reassigned to point to another object or to null.

Example:

// Creating a String object (strings are reference types) in the heap
String myString = "Hello";

// The variable myString_2 references the same object
String myString_2 = myString;

// Creating a new String object in the heap and reassigning the reference
myString = "World";

// Now myString points to a different object, and myString_2 still points to the original