CODEWITHSUNDEEP
javastatic-methodsprivate-members
Netta Steinberg
Netta Steinberg

Reputation: 33

Accessing a private variable through static method in java

Let say I have the following java classes:
Class A:

public class A { 
    private int x; 

    public A(int x){ 
        this.x = x; 
    } 

    public static void main(String[] args) { 
        A a = new A(1); 
        B b = new B(1,2); 
        System.out.println((A)b.x);
    }
}

Class B: 

public class B extends A { 
    public int y; 

    public B(int x, int y){ 
        super(x); 
        this.y = y; 
    } 
}

Why does the compiler marks the access to x on this line 

System.out.println((A)b.x);

as an error, even though I'm trying to access x from the class in which it is defined?

Is it because of:
1. the use of polymorphism?
2. the use of a static method?
3. the use of the main method?

Upvotes: 3

Views: 1464

Answers (7)

mahesh
mahesh

Reputation: 1331

You have follwing issues

  • Compiler will show "Field not visible" Error,Because you trying to access private method of parent class
  • Syntactically. operator has precedence over cast operator
  • And another impotent thing is that No need to cast a child object to parent to access parent specific members, Because they are already inherited to the child, Here the member you are accessing is private ,which is not inherited. Even if you cast to parent you cant access private members using child object.

Upvotes: 1

Balwinder Singh
Balwinder Singh

Reputation: 2282

Basically, two issues exist here.

One being that int x is private so it cannot be accessed from the sub-class.

Now even if you change the access criteria of int x to publicor protected; the code will still not work because (A)b.x will try to typecast an integer (read x) to an object (read A). Instead of this, you should use ((A)b).x

Upvotes: 0

Tom
Tom

Reputation: 16208

Because you are trying to cast an int into A. You need to wrap the cast around the object and then call .x.

Your call is equivalent to (A)(b.x), when it should be ((A)b).x.

public static void main(String[] args) { 
    A a = new A(1); 
    B b = new B(1,2); 
    System.out.println(((A)b).x);
}

Upvotes: 0

NiziL
NiziL

Reputation: 5140

When you write (A)b.x, the compiler try to cast b.x into A, but x is an int

Moreover, you don't need to cast b into A and you can't access b.x because x is a private field.
You may need a getter for this, like b.getX()

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 727027

This is because the dot operator has precedence over the cast operator. This will work, because it forces the cast operator to be applied before the dot operator:

System.out.println(((A)b).x);

Demo on ideone.

Upvotes: 1

Keerthivasan
Keerthivasan

Reputation: 12890

You need to make it ((A)b).x to properly type cast it

Note : You are trying to type cast the property x to type A. That's the error!

Upvotes: 7

jervine10
jervine10

Reputation: 3077

int x is private therefore it can't be reached from outside of the scope of the class. You could mark it as protected. This way it will still have limited scope. Classes that extend A will be able to access the variable freely.

Upvotes: 1

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