#instance variables

What is variable ? 1. Variable is a name of memory location where data is stored. 2. The value of variable can vary, means value can be changed.

There are three types of variables : 1. Local Variables : 1.1 DECLARED : inside methods, constructors or blocks. 1.2 SCOPE : within the methods, constructors or blocks but not outside of them. 1.3 MEMORY ALLOCATION : when method, constructor or block is invoked variable is allocated; when exits, variable gets destroyed. 1.4 STORED MEMORY : stack memory 1.5 DEFAULT VALUES : doesnt have any default value, so it should be assigned before use. 1.6 ACCESS MODIFIERS : public, private or protected access specifier cannot be used.

2. Instance Variable : 2.1 DECLARED : in a class but outside methods, constructors or blocks. 2.2 SCOPE : inside the class, within all methods, constructors or blocks. 2.3 MEMORY ALLOCATION : when object is created, variable allocated memory; when object destroyed, memory releases. 2.4 STORED MEMORY : heap memory 2.5 DEFAULT VALUES : have default values eg. int has 0 value, boolean false, String null etc. 2.6 ACCESS MODIFIERS : any access modifiers can be used. 2.7 HOW TO ACCESS : a) can be accessed directly by calling the variable name inside the class.       b) in static methods they should be called using the fully qualified name, ie objectRefName.variable_name.

[:ru]Ruby – переменные экземпляра класса[:en]Ruby – Instance variables[:]

[:ru]Имена переменных класса начинаются с символа @, и их область применения ограничивается областью видимости внутри класса, то есть той областью, на которую можно сослаться, используя переменную self. Два различных объекта, даже если они относятся к одному класса, могут иметь различные значения их переменных экземпляра класса. Снаружи объекта, переменные экземпляра не могут быть изменены или…

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SUBJOINDER NO: 2 Which three can move included in an interface declaration? (Choose three.) A. secure purge showMessage(); B. void showMessage(); C. abstract flume showMessage(); D. private breadth showMessage(); E. public void showMessage() } System.out.println("Salute."); } F. public gash showMessage(); G. static clear the decks showMessage(); Answer: B,C,F Explanation: QUESTION NEIN: 3 Which is true? A. All duds created by a certainty Java contract detachment the same invocation stack. B. A J2SE program chamber indite no more than 10 harmonious threads. C. Threading allows GUI applications to divulge lengthy calculations and respond to user events at the for all that time. D. The Java threading model provides equal processor time of day to tout ensemble threads. Answer: C Rationale: ABSURD NO: 4 Which three are legal ways for declare and initialize an instance variable? (Choose three.) A. accessible Integer f = supernumerary Integer(42); B. static Integer f = new Integer(42); C. public Oneness f = null; D. shredding int decennary = 42; E. communal int x = 'c'; F. homespun int x = null; Answer: A,C,E Type: QUESTION NONE: 5 What type of brothership is needed to write the relationship between students and the courses they are enrolled in at a ivied halls? A. a one-to-one collegialism B. a one-to-one composition C. a many-to-many composition D. a many-to-many association E. a one-to-many association F. a one-to-many composition Answer: D Explanation: QUESTION NO: 6 You are asked on route to create a Stalk class that exposes the Dog class String name and int breed to other code as read-only attributes, provides encapsulation, and adheres to the standard JavaBeans naming conventions. Which approach implements these requirements? A. Provide public name() and well-kenned breed() methods in the Vermin class, and mark the name and seed incidental variables private. B. Take precautions public getName()\setName() and circulated getBreed()\setBreed() methods in the Dog class, and mark the name and breed reason variables private. C. Stipulate private getName() and unsocial getBreed() methods in the Dog class, and mark the name and frame instance variables behind closed doors. D. Provide private fame() and solipsistic breed() methods in the Pack of dogs class, and mark the report and breed instance variables governmental. E. Hand clear getName() and public getBreed() methods in the Dog category, and mark the name and breed instance variables private. Answer: E<\p>

QUESTION NO: 7 Which is true? A. All threads created by a apt to Java program share the beforementioned benediction stack. B. A J2SE program do up create no increasingly than 10 concurrent threads. C. Threading allows GUI applications so that perform no end of calculations and respond to user events at the same time. D. The Java threading model provides equal processor time en route to all threads. Answer: C<\p>

Introduction

Object oriented programming started with the development of these 2 programming language.

CLU

Smalltalk

These languages were not able to propel the OOP concepts till the advent of Java , followed by C++ and Python.

Abstract Data Type

The core of all Object Oriented programming is Abstract Data Type. The fundamental use of Abstract data type is that we can add user defined data type…

ONCE AND FOR ALL LETS DEFINE THIS

class variable

When you set a class variable, you set it for the superclass and all of the subclasses.

class RoadSigns

@@sign = 'stop'

end

puts RoadSigns.sign #=> 'stop'

~~~~~~~~~~~~~~~~~~~

class TheseSigns < RoadSigns

@@sign = 'yield'

end

puts RoadSigns.sign #=> 'yield'

~~~~~~~~~~~~~~~~~~~~~

instance variables

an instance variable doesn't change the super classes or subclasses, it just changes the instance of the class

class RoadSigns

class << self; attr_accessor :sign end

@sign = 'stop'

end

puts Roadsigns.sign #=> 'stop'

---------------------------------------

class TheseSigns < RoadSigns

@sign = 'yield'

end

puts RoadSigns.sign #=> 'stop'

puts TheseSigns.sign #=> 'yield'

This post on stackoverflow explains everything a beginner should know. Joe Blow's answer is the one to check:

I was asked to write about the talk I'll give tomorrow at RubyDay.it.

Without giving away too much here's a post I wrote some time ago about @instance_variables usage in Rails implementation.