How this is the answer.

[dhwani mathur]

ok ,here is my doubt,may be its a very silly question but i want to know the explanation.

Which one of the following is a correct way to call methodA? Assume data is a non-empty reference to an array object, and lbl is a non-empty reference to a JLabel object.
There are 4 options.
1)methodA(data[], lbl);
2)methodA( data[10], lbl);
3)methodA( data, lbl);
4)methodA( int [] data, lbl);


According to me the answer may be 2,but the answer is 3 can anyone explain me why the answer is 3 .
Thanks in advance.

[dhwani mathur]

Sorry i did not show the method its shown below.

public void methodA (int [] vals, JLabel display){
// do something
....
}

[Christophe Verré]

We don't know the content of the data array, do we ?

[Raghavan Muthu]

Hi dhwani,

3)methodA( data, lbl);

the argument "data" itself would suffice when the actual argument is of array. It actually refers the base address (ie data[0]) of the array thereby in the called method you would get the reference.

I hope i was clear. Aint I?

[Raghavan Muthu]

forgot to add..

in case of your Answer 2, its nothing but the 10th element of the array what you pass to invoke - which will NOT match the syntax of the method declaration.

Is that clear?

[Christophe Verré]

its nothing but the 10th element of the array what you pass to invoke

To which I ask : what if the 10th element is an array of int ?

import javax.swing.*;
 
public class Param { 
 
public static void main(String[] args) {
int[][] data = new int[20][20];
JLabel lab = new JLabel();

Param p = new Param();
p.methodA(data[10], lab);

}

public void methodA (int [] vals, JLabel display){ 

}
}

[ May 29, 2007: Message edited by: Satou kurinosuke ]

[dhwani mathur]

ok what raghavan said is it refers to base address data[0] hence it is passed to which i agree,but the code shown by "satou"

here data is object of array.
int[][] data = new int[20][20];

Here data is given two index ,is it that data is a array collection?

but when you pass it in method it is
p.methodA(data[10], lab);//here a single index [10]

so at this point i am getting confused please can you explain.
Thanks in advance..

[Raghavan Muthu]

Hi Satou kurinosuke,

That was a good point. But i did tell in a general way and context. In that case, the answer 3 seems to be right but not answer 2. Because the question was just having the plain options and not in detail.

In your case, answer 3 is wrong as it would be of sending the address of 2D array data[][]. But since the answer 3 was right, i think it might have been asked in the same assumption as that of mine.

Aint I?

[Raghavan Muthu]

Yes dhwani. You are right on your confusion.

Looking at the source code of the method definition what you gave,

    public void methodA (int [] vals, JLabel display){ 
        // do something 
        .... 
    } 
  

The method definitely accepts only a *1D* array as an actual argument. In that case the answers may vary depends on how you invoke. There are two possibilities..

Case 1: If you have defined a 1D array

 
        int[] oneDimArray = {1,2,3};
 
        JLabel display = null; // for testing sake, having it as NULL 
 
        /* call the method by passing the entire array as its 1D */
        methodA(oneDimArray,display);
 
    

Case 2: If you have defined a 2D array,

 
        int[][] twoDimArray = {{1,2},{3,4}};
 
        JLabel display = null;
 
        /* calling the method by passing with an index as its 2D */
          
        methodA(twoDimArray[0],display);
 
    

But the question was very generically asking which one is right, and by default you can go for the 1D array and not the 2D array i guess. If then, you can even go for data[0][1][2][3] also right?

Hope this clears and helps to certain extent.

[dhwani mathur]

Once again Thanks Raghavan for clearing my doubt.

[Raghavan Muthu]

My Pleasure dhwani...