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Class Composition

Sometimes an object is made up of other objects.
For example, an airplane is made up of a fuselage, wings, engines, landing gear, flaps, and so on.

Class Composition

  1. Caption: As you may remember from high school geometry, a line is defined by two points. Thus, the Line class might have two Point attributes (each one an instance of the Point class).
  2. Caption: Composition is when one class contains another class as an attribute. Composition is indicated in a class diagram by connecting the owning class to the owned class with a line.
  3. Caption: Generally, the type and direction of the relationship are indicated by a few words such as "has a," "owns a," "uses a," or "refers to," followed by an arrowhead indicating the direction of the relationship.
  4. Caption: This picture shows only a single point, when in fact a Line object contains two Point objects. This is indicated by adding the numeral 2 above the line and next to the point.

1) As you may remember from high school geometry, a line is defined by two points. Thus the Line class might have two Point attributes.
As you may remember from high school geometry, a line is defined by two points. Thus the Line class might have two Point attributes.

2) Composition is when one class contains another class as an attribute. Composition is indicated in a class diagram by connecting the owning class to the owned class with a line.
Composition is when one class contains another class as an attribute. Composition is indicated in a class diagram by connecting the owning class to the owned class with a line.

3) The type and direction of the relationship is indicated by a few words such as (has a), (owns a) , or (refers to) followed by an arrowhead indicating the direction of the relationship.
The type and direction of the relationship is indicated by a few words such as (has a), (owns a) , or (refers to) followed by an arrowhead indicating the direction of the relationship.

4) This picture only shows a single point, when in fact a Line object contains two Point objects. This is indicated by adding the numeral 2 above the line and next to the point.
This picture only shows a single point, when in fact a Line object contains two Point objects. This is indicated by adding the numeral 2 above the line and next to the point.