Question

My problem is to store details of people in Java. I looked up at the Oracle website topic How to Use Tables and found out that one can use object arrays(2 dimensional) to store details.

But my interest is to make a dynamic object array so I can store any amount of data and also take input to store those details from the user. For instance, at the beginning of the program I can specify an object array to hold 5 records, but I actually want an array that could add another available location if I need to add more records (dynamic).

Is there a way this is possible in java ? If so, do you happen to know any good places I could start, perhaps a link. Is storing using an Object array the best option?

Answer 1

An array holds homogenous data, i.e. usually the class of everything in every cell of an array is the same. You will likely not want to store a person’s name and his shoe size in fields of the same type, so… let’s drop one of the array’s dimensions. You should declare a class called something like Person and specify within it all the attributes you want to store for a person. Having done that, you will only be wanting to store a one dimensional array (or something) of Person.

Next, note that arrays are fixed in size. If you want to extend an array, you would need to allocate a new, bigger array, copy the contents of the old one into the new one and then go on working with the new one in place of the old one.

That’s a lot of work, and error prone. In the modified words of Apple, there’s a class for that! The older qualified class was Vector, a class where you could store objects and that would grow every time you add a new object to it. Nowadays, the class to use for this (it’s a bit more efficient) is ArrayList. Same thing: You do

ArrayList<Person> myList = new ArrayList<Person>();

and then you can repeatedly

newPerson = new Person("Bruce", "Wayne", 1972, "Gotham City");
myList.add(newPerson);

and you can access folks in the list by doing

int personNumber = 0;
Person retrievedPerson = myList.get(personNumber);

or even

for (Person someone : myList) {
   System.out.println(someone);
}

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EDIT

OK, to store people with an ID and access them by that ID assuming the person ID is an integer, some appropriate code would be:

TreeMap<Integer, Person> myMap = new TreeMap<Integer, Person>();

newPerson = ...
myMap.put(newPerson.getId(), newPerson);

then you can retrieve it with

Person p = myMap.get(id);