1. HAS–A Relationship is Also known as Composition or Aggregation .
  2. There is no specific keyword for this, but most of the cases we can achieve by using new keyword.
  3. The main advantage is re usability.
  4. HAS–A relationship increases dependency between components and creates maintainability problems.

Example:

class Engine{

}

class Car{

Engine e=new Engine();
}

In the above example,class Car has Engine reference.