Java Object Oriented Programming Object Scope

Question

Okay, so far I know a lot about java. Databases, URL, SQL, etc. But so far my books and I have only dealt with single class programs. I was wondering something about OOP.

If I have a class that defines an example object and each example object has it's own array.

Ex.

public class Example {
Array exampleArray;
}

does that mean that every 'example' object has it's own unique 'exampleArray' Array object that can be referenced by "insert objectname here".exampleArray ?

Ex.

Example dataBase = new Example();
int length = dataBase.exampleArray.length();

will this work?

sorry, for some reason the line feed isn't working with my example code

Why don't you try? How could you test your assumptions?

user unknown
– user unknown

2012-12-19 20:35:47 +00:00
Commented Dec 19, 2012 at 20:35 — user unknown
– user unknown, Commented Dec 19, 2012 at 20:35

Bill the Lizard · Accepted Answer · 2012-12-19 20:37:18Z

1

Yes, each Example object will have its own unique exampleArray array object. Typically you would make it a private member variable and access it through methods, though, instead of allowing clients to access the array directly.

answered Dec 19, 2012 at 20:37

Bill the Lizard

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2 Comments

The Militant Hobo Over a year ago

whew, this makes things so much easier. Java books really only focus on one class programs, not large scale data management :/

Bill the Lizard Over a year ago

@user1827733 If you're using an introductory book on Java, most of the examples probably are going to use a single class to illustrate a point. A good book on data structures with Java examples will give you a taste of OOP and larger-scale data management. For example: algs4.cs.princeton.edu/home

Woot4Moo · Accepted Answer · 2012-12-19 20:35:27Z

0

Each object that is generated will have it's own set of attributes. So the following code produces two unique objects:

Example first = new Example();  
Example second = new Example();

with unique attributes for each of these objects.

answered Dec 19, 2012 at 20:35

Woot4Moo

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Comments

Thorn G · Accepted Answer · 2012-12-19 20:35:37Z

0

In this particular example, you will get a NullPointerException because you never assigned a value to exampleArray in your class. But in general, yes, each instance of Example has its own unique array.

answered Dec 19, 2012 at 20:35

Thorn G

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2 Comments

The Militant Hobo Over a year ago

Thank you, I know I would get a Null Pointer, but I put the bare minimum code to get my point across.

Philip Whitehouse Over a year ago

If you say something doesn't work without providing details and claim to know 'a lot' about a language without understanding object's properties, it's understandable we start at the high level, no?

Community · Accepted Answer · 2017-05-23 10:24:45Z

0

This is a bit off topic but I feel worth mentioning. If you intend to make a copy of a Object, you need to be careful that you make a deep copy. Doing so will cause each to act as though they were instantiated normally. If you don't, they will "share" the attribute.

edited May 23, 2017 at 10:24

CommunityBot

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answered Dec 19, 2012 at 20:41

Daniel

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1 Comment

Philip Whitehouse Over a year ago

You mean copy of an object not class.

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