Class (programming) facts for kids

A class and an object are important ideas in object-oriented programming. Think of a class as a blueprint or a plan. It tells you how to build something. An object is the actual thing built from that blueprint.

For example, a blueprint for a car would be a class. It describes what all cars have, like a color, four tires, and the ability to drive. An actual car you see on the road, like your family's car, would be an object made from that car blueprint. You can make many different car objects from the same car class blueprint.

What are Classes?

A class is like a template that a computer programmer writes. It describes the features (called fields or properties) and actions (called methods) that all objects of that type will have.

• Fields are like the facts or data about an object. For a car class, fields could be its color, how many doors it has, or its current speed.
• Methods are like the actions an object can do. For a car class, methods could be `drive()`, `brake()`, or `turnLeft()`.

Let's use our car example again. We could have a class called "Car." This class would say that every car has a `color` (a field) and can `drive` (a method).

How Classes Work Together

Classes can also be related to each other. Imagine a "Vehicle" class. This class would describe things common to all vehicles, like having a `position` and being able to `drive`.

Then, you could have a "Car" class and a "Truck" class. Both "Car" and "Truck" would be types of "Vehicles." This means they automatically get all the fields and methods from the "Vehicle" class.

• The "Car" class could add its own unique features, like how many `persons` it can carry.
• The "Truck" class could add its own unique features, like what `load` it is carrying.

This way, programmers don't have to write the same code over and over. They can put common features in a main class (like "Vehicle") and then add special features in more specific classes (like "Car" or "Truck").

Creating Objects from Classes

Once you have a class (your blueprint), you can create many objects from it. Each object is a unique instance of that class.

For example, from the "Car" class, you could create:

• An object named `myRedCar` (a red car).
• An object named `blueSportsCar` (a blue sports car).

Each of these objects would have its own `color` and `speed`. They can also perform actions like `drive()`. If `myRedCar` drives, it doesn't make `blueSportsCar` drive. They are separate objects.

Using Methods and Fields

To make an object do something or to find out its information, you use its methods and fields.

For example, if you have an object called `myRedCar` from the "Car" class:

• You could ask for its color: `myRedCar.color`
• You could make it drive: `myRedCar.drive(10)` (meaning it drives 10 units of distance).

This way, classes and objects help programmers organize their code. They make it easier to build complex programs by breaking them down into smaller, reusable parts.

Images for kids

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  UML notation for classes