Java Multilevel Inheritance - Protected Instance Variable in Level 1 Class

Question

I have an question which comes under multilevel inheritance in Java. All Three Classes are in Same package

I have class A :

public class A {
   protected int x;
}

public class B extends A {
   public void doSomething {
      // x is visible.agreed, as it is a direct subclass of A
   }  
}


public class C extends B {
   public void doSomething {
      // x is still visible, how come? I mean it is at the 2nd level 
     //  I am confused why?
   }  
}

does it like have any significance? or it is behavior which we have to take it by default?

Solution 1

variable/methods marked with protected modifier are visible to all the classes in the same pacakage and only to subclasses in different packages. below are the example cases.

package a;
class A{
protected int x;
}
class B extends A{
//x can be accessed from this class
} 

class C extends B {
//x can be accessed from this class
}
class D{
//x can be accesed this class but you will have to create A's instance 
}

package B 
class One {
//cannot access x from this class
}
class Two extends A {
//can access x from this class
}

Solution 2

The access level modifiers in Java are:

• public - visible to all code
• protected - visible to all code in the same package and to subclasses regardless of package
• nothing (default) - visible to all code in the same package
• private - visible only to code in the same class (including nested classes)

See, for instance, the Java tutorial Controlling Access to Members of a Class or (for lots of technical details) section 6.6 of the Java Language Specification.

Solution 3

Definition of the keyword

Protected

The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.

I suggest you read this.

Solution 4

The Java protected keyword works its way down to all subclasses (and members of the package). If there was a protected member in Object, any object could access it. By contrast, private is only visible to the local class (and inner classes), and public is accessible by all.

Have a look at this glossary, which shows in-depth how protected members and methods are inherited, and the Java documentation on inheritance.

Solution 5

Please refer this: http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html

The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.

So if your class C shares the package with A and B, its accessible.

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