问题
Please help to understand why does the following code
public class HeapQn1 {
/**
* @param args
*/
public HeapQn1() {
new HeapQn1();
}
static HeapQn1 n = new HeapQn1();
public static void main(String[] args) {
}
}
results in
java.lang.StackOverflowError
at com.rg.test.interview.HeapQn1.<init>(HeapQn1.java:8)
at com.rg.test.interview.HeapQn1.<init>(HeapQn1.java:9)
...
As per my understanding the memory allocation for an object happens in the heap memory and I was expecting an OutOfMemoryError as at some point the heap memory will be full because of repetitive object creation.
On research , I came across that a java constructor is considered a method and that explained the StackOverflowError , until I read the following thread.
When does the Constructor gets called in java?
which says
3. The object is fully constructed/created when the constructor returns.
From what I could gather , the constructor is a method and since the heap memory is much larger than stack memory , the recursive constructor call resulted in StackOverflowError . Is this correct ?
Since no object in the give code will get completely created , will stack frame allocation for constructor actually happen ?
--edit-- For the duplicates pointed out , I do understand what StackoverflowError is . I have mentioned in the question "On research , I came across that a java constructor is considered a method and that explained the StackOverflowError". My question is to understand if a constructor gets a stack frame allocated just like other methods as the object creation is not complete until the constructor returns. Hope this clarifies.
回答1:
Whenever the constructor is called, its return address is pushed onto the stack. As the stack is finite and smaller than the heap memory, you are getting error like StackOverflowError rather than OutOfMemoryError.
The constructor is a method and since the heap memory is much larger than the stack memory, the recursive constructor call resulted in StackOverflowError. Is this correct ?
Yeah, your wild guess is completely correct. Cheers!
回答2:
The constructor is a method, a.k.a. a function. Every time you call it a chunk of memory is allocated to the stack, to store the variables of the function.
Your code creates calls to the constructor function indefenitely, allocating memory to the stack until the memory finishes.
You are obtaining a StackOverflowError and not an OutOfMemoryError, because the quantity of memory dedicated to the stack is smaller than the quantity of memory dedicated to the heap.
EDIT: I have done some test using your code. I've specified a heap memory space of 8M (-Xms8M -Xmx8M) and a stack memory space of 100M (-Xss100M). The computation result is always the error StackOverflowError.
Then, this could mean that no memory is allocated to the heap in this case. As you stated in your question:
The object is fully constructed/created when the constructor returns.
回答3:
Basically what you said is correct, the stack space runs out before the heap space does.
回答4:
You are right: the stack is much smaller than the heap, and no object will be fully created.
回答5:
As per the java all the reference variables are stored in the stack memory space and stack memory space is smaller than heap space that's what we get stackOverFlowException.
来源：https://stackoverflow.com/questions/30911823/java-recursive-constructor-call-and-stackoverflow-error