What is the difference between "Parent c = new Child()" and "Child c = new Child()"?
I am new to Java so please bear with me, I tried looking this question up but I’m having trouble since I don’t know the underlying terms involved in this question.
Assuming:
class Parent {} class Child extends Parent {} What is the difference between:
Parent c = new Child(); and
Child c = new Child(); Thanks in advance for any help you can provide.
At runtime there is no difference.
There is a difference only for the Java compiler (and type checker). In the first case you are declaring that the most informative thing that you know about the c is that it is a Parent, even if the runtime type is more specific.
This has two main effects:
ccan be used when aParentis needed but not when aChildis needed- if you want to change the type of
cto another type (let’s supposeclass Nephew extends Parent) the only necessary thing is to change the instantiation (eg.new Child()becomesnew Nephew()
The second effect is a consequence of the fact that, if the code compiles and c is declared as a Parent, this implies that you are not using any feature which is not already declared in Parent, so every other class which extends from Parent is a valid substitute.
remember this in java- a parent class object can hold the reference to a child class object..
this is exactly what is being done here.
plus look at this Does Parent obj = new Child(); make sense?
