Array or List in Java. Which is faster?

Question

I have to keep thousands of strings in memory to be accessed serially in Java. Should I store them in an array or should I use some kind of List ?

Since arrays keep

Answer 1

Don't get into the trap of optimizing without proper benchmarking. As others have suggested use a profiler before making any assumption.

The different data structures that you have enumerated have different purposes. A list is very efficient at inserting elements in the beginning and at the end but suffers a lot when accessing random elements. An array has fixed storage but provides fast random access. Finally an ArrayList improves the interface to an array by allowing it to grow. Normally the data structure to be used should be dictated by how the data stored will be access or added.

About memory consumption. You seem to be mixing some things. An array will only give you a continuous chunk of memory for the type of data that you have. Don't forget that java has a fixed data types: boolean, char, int, long, float and Object (this include all objects, even an array is an Object). It means that if you declare an array of String strings [1000] or MyObject myObjects [1000] you only get a 1000 memory boxes big enough to store the location (references or pointers) of the objects. You don't get a 1000 memory boxes big enough to fit the size of the objects. Don't forget that your objects are first created with "new". This is when the memory allocation is done and later a reference (their memory address) is stored in the array. The object doesn't get copied into the array only it's reference.