has relationship in class diagram code example

Example: is a relationship vs has a relationship

‘Has a ‘ relationship is also known as “composition or Aggregation”. 
As in inheritance we have ‘extends’ keyword we don’t have any keyword to 
implement ‘Has a’ relationship in java. The main advantage of ‘Has-A‘ 
relationship in java code reusability. For has a relationship we use new keyword

Ex: Car has an engine. We cannot say Car in an engine.

‘is a’ relationship is also known as inheritance. We can implement 
‘is a’ relationship or inheritance in java using extends keyword. 
The advantage of inheritance or is a relationship is reusability of code 
instead of duplicating the code.
  
Ex : 
Motor cycle is a vehicle
Car is a vehicle 
Both, car and motorcycle extends vehicle.