We can create an object of one class into another and that object will be a member of the class. This type of relationship between classes is known as
containership or
has_a relationship as one class contain the object of another class. And the class which contains the object and members of another class in this kind of relationship is called a
container class.
The object that is part of another object is called contained object, whereas object that contains another object as its part or attribute is called container object.
Difference between containership and inheritance
Containership
-> When features of existing class are wanted inside your new class, but, not its interface
for eg->
1)computer system has a hard disk
2)car has an Engine, chassis, steering wheels.
Inheritance
-> When you want to force the new type to be the same type as the base class.
for eg->
1)computer system is an electronic device
2)Car is a vehicle
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Syntax for Containership:
// Class that is to be contained
class first {
.
.
};
// Container class
class second {
// creating object of first
first f;
.
.
};
Below examples explain the Containership in C++ in a better way.
Example 1:
Output:
Hello from first class
Explanation:In the class
second we have an object of class
first. This is another type of inheritance we are witnessing. This type of inheritance is known as
has_a relationship as we say that class
second has an object of first class
first as its member. From the object f we call the function of class
first.
Example 2:
Output:
Hello from first class
Hello from second class
Explanation:In this program we have not inherited class
first into class
second but as we are having an object of class
first as a member of class
second. So when default constructor of class
second is called, due to presence of object
f of
first class in
second, default constructor of class
first is called first and then default constructor of class
second is called .
Example 3:
Output:
Hello from first class
num = 20
Explanation:With the help of containership we can only use
public member/function of the class but not
protected or
private. In the
first class we have returned the reference with the help of
getnum. Then we show it by a call to
showf.
Example 4
