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What Is an Object?
Objects are key to understanding object-oriented technology. You can look around you now and see many examples of real-world objects: your dog, your desk, your television set, your bicycle.
Real-world objects share two characteristics: They all have state and behavior. For example, dogs have state (name, color, breed, hungry) and behavior (barking, fetching, wagging tail). Bicycles have state (current gear, current pedal cadence, two wheels, number of gears) and behavior (braking, accelerating, slowing down, changing gears).
Software objects are modeled after real-world objects in that they too have state and behavior. A software object maintains its state in one or more variables. A variable is an item of data named by an identifier. A software object implements its behavior with methods. A method is a function (subroutine) associated with an object.
Definition:?An object is a software bundle of variables and related methods.
You can represent real-world objects by using software objects. You might want to represent real-world dogs as software objects in an animation program or a real-world bicycle as a software object in the program that controls an electronic exercise bike. You can also use software objects to model abstract concepts. For example, an event is a common object used in window systems to represent the action of a user pressing a mouse button or a key on the keyboard. The following illustration is a common visual representation of a software object.
A software object.
Everything the software object knows (state) and can do (behavior) is expressed by the variables and the methods within that object. A software object that models your real-world bicycle would have variables that indicate the bicycle's current state: Its speed is 18 mph, its pedal cadence is 90 rpm, and its current gear is 5th. These variables are formally known as instance variables because they contain the state for a particular bicycle object; in object-orien
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