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

I'm guessing the original poster is coming from a C++/STL background which is causing some confusion. In C++ std::list is a doubly linked list.

In Java [java.util.]List is an implementation-free interface (pure abstract class in C++ terms). List can be a doubly linked list - java.util.LinkedList is provided. However, 99 times out of 100 when you want a make a new List, you want to use java.util.ArrayList instead, which is the rough equivalent of C++ std::vector. There are other standard implementations, such as those returned by java.util.Collections.emptyList() and java.util.Arrays.asList().

From a performance standpoint there is a very small hit from having to go through an interface and an extra object, however runtime inlining means this rarely has any significance. Also remember that String are typically an object plus array. So for each entry, you probably have two other objects. In C++ std::vector, although copying by value without a pointer as such, the character arrays will form an object for string (and these will not usually be shared).

If this particular code is really performance-sensitive, you could create a single char[] array (or even byte[]) for all the characters of all the strings, and then an array of offsets. IIRC, this is how javac is implemented.