Overriding Member Variables in Java ( Variable Hiding)

Overriding member variables in Java ( Variable Hiding)

When you make a variable of the same name in a subclass, that's called hiding. The resulting subclass will now actually have both properties. You can access the one from the superclass with super.var or ((SuperClass)this).var. The variables don't even have to be of the same type; they are just two variables sharing a name, much like two overloaded methods.

Is there a way to override class variables in Java?

Yes. But as the variable is concerned it is overwrite (Giving new value to variable. Giving new definition to the function is Override). Just don't declare the variable but initialize (change) in the constructor or static block.

The value will get reflected when using in the blocks of parent class

if the variable is static then change the value during initialization itself with static block,

class Son extends Dad {
    static { 
       me = "son"; 
    }
}

or else change in constructor.

You can also change the value later in any blocks. It will get reflected in super class

Explain how variable hiding is working in this Java code

Yes, the B class inherits the foo method. But the variable x in B hides the x in A; it doesn't replace it.

This is an issue of scope. The foo method in A sees only the variables that are in scope. The only variable in scope is the instance variable x in A.

The foo method is inherited, but not overridden, in B. If you were to explicitly override foo with the same exact code:

class B extends A
{
    int x = 6;

    @Override
    void foo()
    {
        System.out.println(this.x);
    }
}

Then the variable that would be in scope when referred to by this.x would be B's x, and 6 would be printed. While the text of the method is the same, the reference is different because of scope.

Incidentally, if you really wanted to refer to A's x in the B class, you can use super.x.

Overriding a super class's instance variables

Because if you changed the implementation of a data member it would quite possibly break the superclass (imagine changing a superclass's data member from a float to a String).

Hiding instance variables of a class

In Java, data members are not polymorphic. This means that Parent.var and Child.var are two distinct variables that happen to have the same name. You're not in any sense "overriding" var in the derived class; as you have discovered yourself, both variables can be accessed independently of one another.

The best way forward really depends on what you're trying to achieve:

1. If Parent.var should not be visible to Child, make it private.
2. If Parent.var and Child.var are two logically distinct variables, give them different names to avoid confusion.
3. If Parent.var and Child.var are logically the same variable, then use one data member for them.

Java method overriding and variable shadowing

Method calls are virtual in Java, which means that the method from an object's actual type is called, regardless of what type the reference was which you used to access the object. Direct field access on the other hand is not virtual, so which r you access will depend on the type of the reference through which you reached it.

Java Inheritance - instance variables overriding

Because inheritance is intended to modify behaviour. Behaviour is exposed through methods, and that's why they can be overridden.

Fields are not behaviour but state. You don't need to modify that, nor the private methods employed by the superclass. They are intended to allow the superclass to do it's job.

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