Question

Can anybody explain to me how objects are stored and removed from heap memory of Java. I’m looking for more information than simply:

an Object will removed when there is no reference

For example:

class Heap
{
    void add(int a, int b)
    {
        System.out.println(a+b);
    }

    public static void main(String ar[])
    {
        Heap obj=new Heap();
        obj.add(4,3);
        obj.add(5,5);
    }
}

Here how is obj and a, `bJ allocated in java memory. When will it be removed from memory by the JVM?

Answer 1

Put simply:

1. obj is allocated on the heap when new Heap() is invoked.
2. a and b both are allocated on the stack (primitive types, method arguments), the memory will be released upon returning from add.
3. obj will be removed from the heap whenever the garbage collector runs after the execution is out of main (the specification does not guarantee the GC will at any given time, it’ll figure out when’s the right time on its own, although almost-full-heap is probably a very common trigger) – in this case though, since the program would terminate, it would be immediately after returning from main.