Instance Definition
Basic – Computing
What Is an Instance?
Definition in Programming and Cloud Computing
An instance is a single, concrete occurrence of a class, created while a program runs and holding its own data in memory. The class defines what something can be. The instance is one specific version of that thing, with real values filled in.
The same logic shows up in cloud computing, where an instance is one running copy of a virtual machine created from a template image. Different layer of the stack, identical idea: template on one side, working copy on the other.
What Is an Instance?
Start with the class. A class is program code that works as a template: it defines the properties an object will have and the things it can do. On its own, a class does nothing. No memory is allocated, no data exists, nothing runs.
An instance is what you get when the program actually uses that template. At runtime, the program allocates memory, fills in the properties with real values, and hands you back something you can work with. That act of creating an instance is called instantiation, and Oracle’s official Java documentation defines an object in exactly these terms: a runtime entity built from a class, bundling its own state and behavior.
One class, unlimited instances. Your program can create a single instance or ten thousand, and each one lives independently. Change a value inside one and the others don’t notice.
You’ll hear “object" and “instance" used almost interchangeably, and in casual conversation that’s fine. The precise distinction: “object" refers to the thing itself sitting in memory, while “instance" describes its relationship to the class it came from. Every object is an instance of some class.
Class vs. Object vs. Instance
The cleanest way to keep the three terms straight is the blueprint analogy.
| Concept | What it is | Analogy | Exists at |
|---|---|---|---|
| Class | Template code defining properties and behaviors | The architect’s blueprint | Design time (written in code) |
| Object | A concrete entity in memory built from the class | A built house | Runtime |
| Instance | That object, described by its relationship to its class | This house, built from thatblueprint | Runtime |
A blueprint isn’t a house. You can’t live in it. But from one blueprint, a builder can put up an entire street of houses, each with its own address, paint color, and owner. The blueprint is the class. Each house is an object. And each house is an instance of the blueprint that produced it.
What this means: class and instance are not two kinds of the same thing. One is a definition, the other is a live occurrence of it.
Instance Variables Explained
Data has to live somewhere, and in object-oriented programming it lives inside instances.
An instance variable is a variable whose value belongs to one specific instance. Every instance gets its own copy. If your program creates two instances from the same class and changes a variable in the first, the second keeps its original value. Nothing is shared.
Contrast that with a class variable (called a static variable in some languages), which belongs to the class itself. One copy exists, and every instance sees the same value. Class variables suit things like counters or shared configuration. Instance variables hold the state that makes each instance itself: this customer’s name, this order’s total, this car’s mileage.
A quick rule of thumb: if the answer to “whose value is this?" is “this particular one’s," you’re looking at an instance variable.
How Instances Work in Practice
Say you’re writing a program that deals with cars. You write a class called Car that defines the generic properties every car shares: manufacturer, model, color, mileage, top speed, transmission type. The class also defines behaviors, like accelerating or shifting gears.
Then you instantiate it. You create an instance called myCar and fill in the details:
- Manufacturer: Toyota
- Color: black
- Mileage: 10,000 km
- Transmission: automatic
myCar is now a unique occurrence of the Car class. It occupies its own space in memory, and your code can read or change its properties directly: update the mileage after a trip, repaint it by assigning a new color value, whatever the program needs.
Create a second instance called rentalCar with different values, and the two coexist without interfering. Both came from the same template. Neither shares data with the other. That separation is the entire point, and it’s what lets a program juggle thousands of customers, orders, or sessions with one set of class definitions.
Instances in Cloud Computing
The programming concept escaped into infrastructure vocabulary a long time ago, and it kept its meaning.
In cloud computing, an instance is a single virtual machine running on a provider’s infrastructure. AWS, Azure®, and Google Cloud all use the term for exactly this. The template in this case is a machine image: a saved snapshot of an operating system plus installed software and configuration.
Launch an instance and the provider creates one running copy of that image, with its own allocated CPU, memory, and storage.
Sounds familiar? Image is to instance what class is to object. One image, unlimited running copies, each with its own state.
The same template-to-copy model is what makes desktop virtualization practical for businesses. Instead of configuring machines one at a time, you define the environment once and spin up identical instances as your team grows.
That’s the mechanism underneath Desktop as a Service: we host the instances, and your team reaches a full desktop from a browser. Each user session runs against real, allocated resources rather than a machine sitting under a desk.
The vocabulary transfers cleanly because the problem is the same. Templates are cheap to define and expensive to duplicate by hand. Instances automate the duplication.
For related concepts, see our glossary entries on virtual machines and virtualization.
Instance Definition Frequently Asked Questions
Q: What’s the difference between an object and an instance?
In practice, almost nothing, and most developers use the terms interchangeably. Strictly speaking, “object" names the entity in memory, while “instance" describes its relationship to a class. Every object is an instance of the class that created it.
What is an instance variable?
An instance variable is a variable whose value belongs to one specific instance of a class. Each instance holds its own copy, so changing the value in one instance never affects another.
Q: What does “instantiate" mean?
To instantiate means to create an instance from a class. The program allocates memory for the new object and typically runs a constructor to set its starting values.
Can one class have multiple instances?
Yes, and that’s the normal case. A single class can produce any number of instances, each with its own independent data. A design that deliberately limits a class to one instance is called the singleton pattern.
What is an instance in cloud computing?
A cloud instance is one running virtual machine created from a machine image. The image is the template; the instance is the live copy with its own CPU, memory, and storage allocation.
Is a virtual machine the same as an instance?
Mostly. “Instance" is the term cloud providers use for a virtual machine running on their platform, so every cloud instance is a VM. People rarely call an on-premise VM an instance, though the underlying technology is the same.
