Java private variables in Ruby

rubyonrails-talk
1

Hi

How would I achieve in Ruby what the following line does in Java?:

private BufferedImage buf;

I need a new BufferedImage, but I don't want to initialize it yet.

Thanks. Jennifer

2

You don't need to declare things in advance in ruby, and typing is done dynamically so the ruby equivalent of that statement is basically an empty line :slight_smile:

Fred

3

Hi Fred

Thanks for answering my question again. I wanted to make it a method variable because I wanted to initialize it within the scope of a conditional loop as well as use it later on in the action method. So ,that's why I thought I should declare it in the scope of the method. Is there something else I should be doing?

JB

4

Attributes of a class are private by default. You have to use attr
acessor ang getter to get access to them.

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5

You don't need to declare variables in advance in ruby like you do in java (1 exception: if you create a variable inside a block it won't be visible outside the block unless it already existed). If you really must buf = nil is all you need.

Fred

6

Yea one of the great parts about ruby is how its dynamically typed. If you want to declare a private variable accessible throughout the class use an instance variable:

@buf = BufferedImage.new

or in a local scope (not accessible outside the class):

buf = ...

if you use an instance variable and want to access it outside the class (public interface):

attr_accessor :buf

that automatically creates "getter" and "setter" for @buf which look like:

def buf   @buf end

def buf=(value)    @buf=value end

7

Hi --

Attributes of a class are private by default. You have to use attr acessor ang getter to get access to them.

Or, to put it slightly differently: An object's instance variables are only visible to that object (i.e., only visible when 'self' is that object). If you expose an instance variable through getter and/or setter methods, then you've given your object an "attribute", though there's no real distinction between getter/setter methods that are implemented as simple wrappers around instance variables and those that aren't.

So instance variables are not, themselves, attributes; they're just instance variables, and they can (but do not have to) participate in the creation of attributes. And there's no language-level difference between an "attribute" and a getter and/or setter method in general (whether it uses instance variables or not).

David