CODEWITHSUNDEEP
oopclass
Steven Matthews
Steven Matthews

Reputation: 11285

Difference between a child of a class and an instance of a class?

What's the difference between the child of a class and an instance of a class? Both seem to inherit code from their "parent". Is the difference that an instance of a class is executed code, versus a child of a class merely being around to create additional instances?

Upvotes: 2

Views: 838

Answers (2)

slugster
slugster

Reputation: 49984

A class is nothing more than a definition, a template, a pattern. An instance of that class is a copy of that definition that has been allocated memory space in which to hold its data. It's like saying a cake is an instance of a cake recipe.

A child of a class is literally that - the parent forms a base definition, which the child then extends or enhances. It's a variation on the parent, much like a chocolate cake is a variation (or it extends) a basic cake recipe.

Note that this very simple explanation of OO concepts hides how this stuff is actually implemented at the machine level. A class can contain methods (operations) - there is only one copy kept of these methods, instantiating a new instance of the class doesn't make a fresh copy of the methods. Instead memory space is allocated to the new instance, and pointers will be used to point to the actual code that should be implemented for each method. Each instance does have its own copy of data (attributes) though.

Upvotes: 5

xdazz
xdazz

Reputation: 160853

For example with php:

class A {
  //...
}

class B extends A {
  //...
}
$a = new A();

We say B is the child of A, $a is an instance of A.

Upvotes: 0

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