Thread: Maximum size of Collections

Hi every one!
I am just not sure of some theory in collections, I'm just a less than a year java programmer.

Most people in the internet said, ArrayList and LinkedList maximum capacity depends on the memory allocated to the JVM. But according to few people those list has a maximum capacity of Integer.MAX_VALUE.
According to my experiment, those list has a maximum capacity of Integer.MAX_VALUE since the get method of List accept a parameter of int primitive type (index of element), therefore we can conclude that the maximum capacity of List is equal to Integer.MAX_VALUE.

But what about the Map? get() method of map accepts object(the key of the map). So does it mean that the maximum capacity of Map depends on the memory allocated to our JVM? Or its maximum size is Integer.MAX_VALUE also just like Lists and Arrays? Is there a way to prove it? Is Map designed to hold infinite number of data (disregarding the heap memory space exception)?

And also about Stack, Deque? is it also the same as Map (in terms of maximum capacity)?

Thanks

The maximum size of every collection is different.
Yes, the ArrayList probably has a maximum size of (Integer.MAX_VALUE - c), but the LinkedList might very well have infinite size.
You are correct, that the get(int index) method takes an integer and thus you are capped by Integer.MAX_VALUE, but that does not mean that the list itself might not contain more objects then what you can get.
You could iterate over all elements in the LinkedList and maybe get more then Integer.MAX_VALUE.

Same is true for maps. Some maps might have a maximum size depending on Integer.MAX_VALUE while others dont. To know for sure you could look at the source code and / or the documentation.
The interface itself does not make any restrictions, the implementations can deal with this as they please.

This is a very good question. I'd say the maximum practical capacity of the data structures is less than or equal to the maximum value of the data type accepted or returned by their size-related methods (int size(), E get(int index), etc.). I say "practical" because even if the underlying implementation can store more elements than max-int, once these methods stop working as documented, the data structure ceases to be reliable (ignoring performance considerations in this context.)

Note that the API docs do give clues on the maximum practical capacity. See:

• Collection (Java Platform SE 7 ) : "If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE."
• List (Java Platform SE 7 ) : "IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())"
• Map (Java Platform SE 7 ) : If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

See also the following for further discussions on this topic:

• java - What happens when HashMap or HashSet maximum capacity is reached? - Stack Overflow
• java - Maximum size of HashSet, Vector, LinkedList - Stack Overflow

Originally Posted by dicdic

According to my experiment, those list has a maximum capacity of Integer.MAX_VALUE since the get method of List accept a parameter of int primitive type (index of element), therefore we can conclude that the maximum capacity of List is equal to Integer.MAX_VALUE.

Using get is not the only way to access members of a collection

for (String str : list)
// Iterates through each String element of the list

Using get is not the only way to access members of a collection

I am not saying that the only way to access the element is the get() method. Of course there is Iterator interface that can iterate the element . What I'm pointing out is that the size might be equal to Integer.MAX_VALUE since get() method accepts only integer type.

I am still in further study of what cornix and jashburn suggested to read before I post the response of another question.