It depends on what you are doing. Arrays and lists have unique characteristics, as do hashmaps and all sub-categories of arrays/lists.
arrays are simple data types. They are mutable, however their length is not int[] array = new int[4]; creates a new empty array of ints . To set an int its as simple as: array[0] = 5 System.out.println(array[0]); will obviously be 5 thats pretty much all there is to it edit: heres a more in depth description:http://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html you might want to google the advantages of arrays over ArrayLists and vice versa
I don't think there is a data type that CANT do that. Just be aware that storing large amounts of entities repeatedly/for extended periods of time is bad habit. Example: ArrayList<Entity> or Entity[]
If you are looking for the types of Lists maps, etc in java look up "Data Structures in Java" or just check out http://www.informatics.susx.ac.uk/courses/dats/notes/html/notes.html
^ ^ | Tried That | Eclipse gave me errors... Type safety: The method add(Object) belongs to the raw type List. References to generic type List<E> should be parameterized: Code: successfullEntities.add(entity); - Type mismatch: cannot convert from element type Object to Entity: Code: for(Entity sE : successfullEntities) { EDIT: It has now stopped showing errors after save :? (<-- New smiley)