Private means

[Raghu Shree]

Can one object acess a private variable of another object of the same class ?

Ans: Yes

Could any one explaine this rule with one example?

[Mark Spritzler]

Here is an example

 
 
public class A {
    private String name;
 
    public A(String name) {
this.name = name;
}
    public String getAnotherName(A a) {
        return a.name;
    }
 
    public String getName() {
return this.name;
}
}
 
 

and

 
 
public class Test {
    public static void main(String[] args) {
        A a = new A("Hello");
        A b = new A("World");
        System.out.println("getanotherName: " + b.getAnotherName(a));
        System.out.println("a.getName: " + a.getName());
        System.out.println("b.getName: " + b.getName());
 
    }
}
 

When run, the following results occur

 
getanotherName: Hello
a.getName: Hello
b.getName: World
Press any key to continue . . .
 

Hope that helps.

Mark

[Mark Spritzler]

"shree shree"-
Welcome to the JavaRanch! Please adjust your displayed name to meet the

JavaRanch Naming Policy.

You can change it

here.

Thanks! and welcome to the JavaRanch!

Mark

[Tony Morris]

class C
{
class X
{
private int x;
}
 
class Y
{
// class Y accessing private member x of class X.
// To find out how this is possible, read the bytecode of the compiled class files.
// Or read the JLS and VM Specification.
private int y = new X().x;
}
}

[Raghu Shree]

Hi Mark,
whots wrong in my name ?

[Mark Spritzler]

You need to have your real first and real last names, not one or the other repeated.

Funny, you fixed it as I posted this. Your name now complies. Thanks.

Mark
[ April 06, 2005: Message edited by: Mark Spritzler ]

[Anupam Sinha]

Hi Mark

I am not able to understand this concept. The code belows uses two different classes and objects of these classes to access a private variable.

class A
{
    private String name;
    A(){}
    public A(String name)
    {
        this.name = name;
    }
    public String getAnotherName(A a)
    {
        return a.name;
    }
    public String getName()
    {
        return this.name;
    }
} 
public class Test
{
    public static void main(String[] args)
    {
        A a = new A("Hello");
        B b = new B("World");
        System.out.println("getanotherName: " + b.getAnotherName(a));
        System.out.println("a.getName: " + a.getName());
        System.out.println("b.getName: " + b.getName());
    }
}
 
class B extends A
{
    private String name;
    public B(String name)
    {
        this.name = name;
    }
    
}

Forgot to attach the output.

getanotherName: Hello
a.getName: Hello
b.getName: null
[ April 06, 2005: Message edited by: Anupam Sinha ]

[Animesh Shrivastava]

Anupam,
See variables are never overridden, they are hidden. This means that if the variables are called under class A's scope, variable of class A will be visible. While if its under class B's scope, variable of class B will be visible.
So here since "name" variable is initialized to "World" in class B but this is hidden in class A, in A the same variable is null. Class A cannot see class B's varaible. So it displays null.

[Raghu Shree]

Hi Animesh
1. Class B has getName() method. Bcoz it is inherited from A.
2. Now class B object called the getName() method: b.getName().
3. B has own memeber variable b and initialized as world
4. Why it is print null.

So here since "name" variable is initialized to "World" in class B but this is hidden in class A, in A the same variable is null.

But the below code is work fine.

class A
{
   int a;
   A()
   {
      a=100;
   }
   int getA()
   {
   return a;
   }
 }
 class B extends A
 {
 
    int b;
    B()
    {
    b=200;
    }
    int getB()
    {
    return b;
    }
 }
 
 public class C
 {
    public static void main(String args[])
    {
    A a = new A();
    B b = new B();
    System.out.println("A Value From A Scope " +a.getA());
    System.out.println("B Value From B Scope " +b.getB());
    System.out.println("A Value From B Scope " +b.getA());
    }
 }

Output:
A value From A Scope 100
B value From B Scope 200
A value From B scope 100

How is it possible.
I am Confused. Is anything I understand wrong?

[Animesh Shrivastava]

So whats the problem u r having, i guess its in this statement
System.out.println("A Value From B Scope " +b.getA());

right?
Ok whats happening here is that since methods are inherited from super class to sub class, so u can very well access the method getA(). Now since this method accesses the variable a, which is initialized to 100, u get the output. Now one more thing, see when u create an instance of a class, beore the instance is created constructor of super class is also run and in effect all its instance initializers. So lets see whats happening here

When u create an object of A, u also initialize the variable a to 100;
When u create an object of B, u initailize A's instance members( A is super class of B, here a is initialized to 100) as well as instance members of class B
U getting it?
So when getA() is called from Class A, u get the variable 100 printed for a.

Now lets take up the previous example for u.
In that example :

  
 
public class Test {
    public static void main(String[] args) {        
        A a = new A("Hello");
        B b = new B("World");
        System.out.println("getanotherName: " + b.getAnotherName(a));
        System.out.println("a.getName: " + a.getName());
        System.out.println("b.getName: " + b.getName());
    }
}
 
class A{   
 private String name;
    A(){
      this.name = "Hello"; //line 1, [B] I have added this [/B]
    }
    public A(String name)    {
        this.name = name;
    }
 
    public String getAnotherName(A a)    {
        return a.name;    }
    public String getName()    {
        return this.name;
    }
}
 
class B extends A{
    private String name;
    public B(String name)    {
        this.name = name;
    }
}

See above, i have modified the code for u.
When u create an instance of Class A, u get name initialized for the class.
When u create an instance of Class B, the no-arg constructor of class A is also run because by default JVM inserts the statement "super()". In ur earlier case, since A's default constructor was being run, u got the value as null for the string name.
But now look at the code i have given, here in the no-arg constructor of A, i am also initializing the variable name of A.
Run the program and tell me if u have any problem in justifying the output.

Thanks

[Raghu Shree]

Hi Animesh
Thanks lot. Now I am cleared in Inheritance with member hiding.

[Anupam Sinha]

Hi Animesh

Thanks for the reply. I wanted to know that even when a (Object ref. to A) and b (Object ref to B) belong to two different classes then also

System.out.println("getanotherName: " + b.getAnotherName(a));

the above line executes.

In the code above an Object of type B is changing an Object of Type A.

So does it mean "Can one object acess a private variable of another object of the same class and a diferent class aswell.

[Animesh Shrivastava]

So does it mean "Can one object acess a private variable of another object of the same class and a diferent class aswell.

No an object cannot directly access the private variable of another object of the same class. It can only be done using a public method which accesses the variable , like its done using anotherName() method

[Jim Yingst]

[Animesh]: No an object cannot directly access the private variable of another object of the same class.

I guess that means you haven't actually tried it, eh?

[Raghu Shree]

Hi jim,
Is it possible? how ?

[Joyce Lee]

Animesh: No an object cannot directly access the private variable of another object of the same class.

The example given by Mark has demonstrated that it's possible.

Extracted from the second post of this thread.

  
public class A {
    private String name;
 
    public A(String name) {
        this.name = name;
    }
    
    public String getAnotherName(A a) {
        [B]// accessing a private variable of another object of the same class
        return a.name; [/B]
    }
 
    public String getName() {
        return this.name; 
    }
}

[ April 07, 2005: Message edited by: Joyce Lee ]

[Mark Spritzler]

Animesh and Raghu gave really good explanations there.

Mark