Maximum size of array and arraylist..?

[santhosh.R gowda]

Dear all
what is the maximum size of array and ArrayList is it depends on the size of heap pleaes just go through the code

  
public class size
{

  public static void main(String args[])
  {
     System.out.println(Runtime.getRuntime().getMemory()); // the value is 2031615
     int arr[] = new int[2031617];
  }
}

In this code the i had added plus 2 to the size of total memory int int array but my code is not giving outofmemory error
Please help me

[Sagar Rohankar]

Runtime.getRuntime().getMemory()
There is no method like "getMemory()" in Runtime class.
What you need is max memory allocated to JVM and find it using "maxMemory()" method, and then assign this max memory to array, you'll get OutOfMemory exception.

[santhosh.R gowda]

Sorry for ht ewrong method entry i had given totalMemory() only but its not giving error

[Sagar Rohankar]

  
public class Foo
{

  public static void main(String args[])
  {
     System.out.println(Runtime.getRuntime().maxMemory()) ; 
     int arr[] = new int[66650102]; 
  }
}

I tried this code, ant it successfully throwing an exception !! Which code your trying ? Can you use "maxMemory()" ?

[santhosh.R gowda]

Ya its throwing error but when we use size less than maxMemory() ie 666501109 also its throwing error we are not getting the exact value of the size limit please give me the exact number(maximum size) that the array will not throw error up to that value

[Adam Michalik]

Arrays are non-negative integer indexed , so maximum array size you can access would be Integer.MAX_VALUE/2. The other thing is how big array you can create. It depends on the maximum memory available to your VM and the content type of the array. Each array element has its size, eg. byte = 1 byte, int = 4 bytes, Object reference = 4 bytes (on a 32 bit system). So if you have 1 MB memory available on your machine, you could allocate an array of byte[1024 * 1024] or Object[256 * 1024]. Answering your question - you can allocate an array of size (maximum available memory / size of array item).

[Campbell Ritchie]

Adam Michalik wrote:Arrays are non-negative integer indexed , so maximum array size you can access would be Integer.MAX_VALUE/2.

Integer.MAX_VALUE, surely? Not divided by 2.

[Adam Michalik]

Yes, of course (I had in mind that the maximum value is half of the total possible integer numbers)

[santhosh.R gowda]

" Adam Michalik wrote
Object reference = 4 bytes (on a 32 bit system)

I think its 8 bytes right for 32 bit system and 16 bytes for 64 bit system

[Adam Michalik]

santhosh.R gowda wrote:

Adam Michalik wrote:
Object reference = 4 bytes (on a 32 bit system)

I think its 8 bytes right for 32 bit system and 16 bytes for 64 bit system

After some research, I'm not so sure it is explicitly determined. See the other thread.
On the other hand, on a 32 bit system, a memory pointer takes 4 bytes, so I don't know if it was reasonable to have 8 byte references... What's more, an 8-byte reference would not fit into a 32-bit processor register, which in turn would be slowing down object reference resolution. Do you have any more info on usage of 8-byte references on a 32-bit system?