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Asked: 2026-05-10T22:16:04+00:00

I can not distinguish the difference between aggregating and holding. What does it mean

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I can not distinguish the difference between aggregating and holding. What does it mean in terms of, let`s say, C++?
I suppose when the object of class A holds (or instantiates) objects of class B, it uses it to perform some functions by itself.
For example:

class A {  int state;  public:    A(int s): state(s) {}   int inc() { return state++; } }; class B {   int app;   string s; public:   B(): app(0), s('') {}   B(int A, const string& str): app(A), s(str) {}   void f(int p);   ~B() { app = 0; s = ''; } }; void B::f(int p) {    A mA(p);    app = mA.inc(); }

And the aggregation of object of class A would be like this:

class B{  A t;  //... }

Please give me a link to a web-site or to a place in a book where I can find clear definitions in terms of OO language what exactly each kind of relationship between classes is.

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1 Answer

  1. Holding another class means that a class is associated with another class through a parent child relationship. For example a Path has a list of points. The Path is the parent of the List of Points which is the parent of the individual points.

    Aggregating means taking different classes and putting them behind a interface so they appear as one class. For example a FileDialog will have several button class, a text input class, a listview/treeview class and so on. But to the rest of the system it just had methods to be activate, maybe assign a default filename, and retrieve the rest.

    The fact it is comprised of all the other classes is immaterial to other classes using it as a filedialog.However it works by aggregating all the classes to perform the expected behavior.

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