A variable is used as a storage location that holds a value within a object. It is used to represent an attribute or property of an object - and can be used to store and retrieve data.

In OOD variables are typically defined as part of a class -which defines the attributes or properties of an object created from that class.

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These variables are also known as instance variables and member variables - they are declared within the class definition but outside of any method. 

Instance variables hold data that is specific to each object created from the class and their values can be accessed and modified through the objects methods.

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So if the class (object) were 'Car' - instance variables would be 'make, model, colour, year' - 

 

Each object created from the Car 'class' would have it's own values for these variables (eg: Mercedes, Ferrari, McClaren) . These values can be accessed and modified through the objects methods.

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Methods - //// 

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In OOD a method is a block of code that defines the behaviour of an object. It is a function that is associated with a particular object (class) and can be called to perform a specific action or to manipulate the objects state (the particular condition that someone or something is in at a specific time).

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METHODS are defined (precisely marked or stated) within the class and they can access and modify the objects attributes.

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Methods are also responsible for implementing *(put something into effect) the objects behaviour - which means they define how the object responds to different events and interactions (with other objects // or classes) - 

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For example - in the car class the 'accelerate method' might increase the cars speed, whilst the 'brake method' might decrease it. These methods would be defined (precisely marked or stated) within the class and could be called on in any instance of the class to modify the cars state (the particular condition that someone or something is in at a specific time). 

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Methods can also take parameters - 

1. a numerical or other measurable factor forming one of a set that defines a system or sets the conditions of its operation.

2. a limit or boundary which defines the scope of a particular process or activity.

which are passed to them when they are called and they can return values , which can be used by the calling code.

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Again for example: 

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In object-oriented design, a method is a block of code that defines the behavior of an object.

 

It is a function that is associated with a particular object and can be called to perform a specific action or to manipulate the object's state.

 

In the above instance the code we wrote and assigned to an object meant that the phrase 'Hello World' appeared when we hit the space bar. 

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That would be the 'Hello World' method. 

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