Variable shadowing in Java [duplicate]

Answer 1

Variables aren't polymorphic. When you access m.name, that will always use the Mammal.name field which is part of that object, regardless of the execution-time type of the object. If you need to get access to Zebra.name, you need an expression with a compile-time type of Zebra.

The makeNoise method is called virtually though - the implementation used at execution time does depend on the type of the object.

Note that if you make all your fields private - which is generally a good idea anyway - this doesn't end up being an issue.

This is actually hiding rather than shadowing. See JLS section 8.3 for details on hiding, and section 6.4.1 for shadowing. I can't say that I always keep the differences straight...

Answer 2

Variable names in Java are resolved by the reference type, not the object they are referencing. So, m.name refers to the variable name in Mammal even dough m is a Zebra.

Answer 3

There is no variable overriding in Java, you declared name in both the parent and the child but you referred to it through a parent reference variable. That's why you got 'furry'.

There is overriding for methods, which is why you got bray. Because on runtime it looked at the real object in the heap and saw it's a Zebra.

Answer 4

Output comes as "furry bray". Please explain this.

fields in java programs are not accessed via dynamic lookup. Instead they are resolved statically while compile time. That's why you are getting furry for m.name. Whereas, methods in java programs are accessed via dynamic lookup. That's why you are getting bray for m.makeNoise().

And how can we access the name variable, the one having "stripes " in it?

And if you want to access Zebra.name , you should type cast m to 'Zebra'.This would look like this:

System.out.println(((Zebra)m).name + m.makeNoise());

UPDATE
The phenomena that is exhibiting here is the result of Fields Hiding rather than variable shadowing.

Answer 5

It happened because your field name from Mammal is just hidden by name field from Zebra. You can then access it simply by casting to required type.
On the other side makeNoise() method overrides same method from parent so you can't access implementation from parent anymore.