Java offers two types of constructs where you can store multiple values or objects of the same type: arrays and collections (for System Dynamics models AnyLogic also offers HyperArray, also known as “subscripts”, — a special type of collection for dynamic variables).
Array or collection? Arrays are simple constructs with linear storage of fixed size and therefore they can only store a given number of elements. Arrays are built into the core of Java language and the array-related Java syntax is very easy and straightforward, for example the nth element of the array can be obtained as array[n-1]. Collections are more sophisticated and flexible. First of all, they are resizable: you can add any number of elements to a collection. A collection will automatically handle deletion of an element from any position. There are several types of collections with different internal storage structure (linear, list, hash set, tree, etc.) and you can choose a collection type best matching your problem so that your most frequent operations will be convenient and efficient. Collections are Java classes and syntax for obtaining, e.g., the nth element of a collection of type ArrayList is collection.get(n).
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