CODEWITHSUNDEEP
javainheritanceaccess-modifiersrestriction
user8001621
user8001621

Reputation: 149

Restricting parent class members to its immediate child class only

Suppose I have four classes in java with given hierarchy.

class A {}
class B extends A {} 
class C extends B {} 
class D extends C {}

As per my understanding all the accessible fields of class A will be available to all its child classes through inheritance. Now what if I want few fields of class A to be available to class B only.

Is there any way in java so that I can restrict certain fields of parent class to its immediate child class only?

Upvotes: 14

Views: 3986

Answers (6)

Prashant Gaikwad
Prashant Gaikwad

Reputation: 1

By OOPS concept: Designed behavior of class cannot be different for one class and different for another class in inheritance concept.

To stop inheriting the fields to child class make those fields as sealed i.e. private. And if you required fields to be access by only immediate child then mark the fields as protected.

If you need access the fields till last leaf node child class (in this case till Class D) then mark the fields as public.

Or by while designing the class into the components you can restrict the inheritance of one class from another component through OOPS access modifiers at class level.

Upvotes: 0

Jul10
Jul10

Reputation: 503

A workaround to achieve the purpose could be refactoring.
Defining an interface or an abstract class Class , implemented/subclassed by A and B, with the variables and the methods in common beetween the two classes.
C and D extend A, inheriting the methods implemetend in A.
The choice beetween the use of interface/abstract class for Class is dictated from the need of reuse common fields and methods in A and B or not.

Upvotes: 0

Nir Alfasi
Nir Alfasi

Reputation: 53525

Not that I would do anything like this in production, but here you go:

class A {
    private int a = 1;

    public int getA() {
        if (getClass().equals(A.class) || 
            getClass().getSuperclass().equals(A.class)) {
            return a;
        } else {
            throw new UnsupportedOperationException("hahaha");
        }
    }        

    public static void main(String[] args) {
        A a = new A();
        B b = new B();
        C c = new C();
        System.out.println(a.getA());
        System.out.println(b.getA());
        System.out.println(c.getA());
    }
}

class B extends A {}

class C extends B {}

So basically you can use this trick to allow only classes you want (using either the blacklist or whitelist approach) - to call getA().

OUTPUT:

1
1
Exception in thread "main" java.lang.IllegalStateException: hahaha
    ...

Upvotes: 11

Ananta
Ananta

Reputation: 700

You can set all your attributes private and access them using getters. Then you can control the visibility and override it.

An example with 3 classes:

    class A{
        private String test = "Test123";
        protected String getTest(){return test;};
    }

    class B extends A{
        @Override
        protected String getTest(){return "no";};
    }

    class C extends B{
    }

Here the class A shares the test attributes only with B. B can access the A attribute with super.getTest() C cannot access the test.

Its a much cleaner approach than check the class type.

Upvotes: 0

Ronak Thakkar
Ronak Thakkar

Reputation: 2525

Restricting parent class members to its immediate child class only, For that,

Java provides protected access modifier in which, You can access class members:

1) Within class

2) Within package and

3) Outside the package by Subclass only.

If you want to restrict data members to the immediate child class, then What you can do is:

Declare One class as below:

package com.firstpackage;

Class A{
 protected int a;
}

Now Use the child class in another package like this:

package com.secondpackage;

Class B extends A{
 //Access data members of class A
}

Now if you declare, Class C and D in package com.secondpackage; and extends them from Class B, Then these two classes (Class C and D) are not the direct children of Class Aand of course not in the same package in which Class A is implemented. So the data members of Class A is not accessible in Class C and D.

Upvotes: 5

Samir Bhatt
Samir Bhatt

Reputation: 3261

This is not right class design but, if you really want to do this, you can manage this scenario.

Like, you want to restrict parent class members to other than immediate child class, you can use protected access modifier and put other class in another package.

As per your example,

Class A and Class B will be in the same package and Class C,D will be another package. You can use protected access modifier for Class A's member.

Upvotes: 2

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