Array probs

[reon]

Did anybody please explain me wat is the problem here...
it is showing a null pointer exception...

class array
{
String var;
public static void main(String args[])
    {
    array obj[];
    obj = new array[1];
    obj[0].var="1";
    System.out.println(obj[0].var);
    }
}

[shana07]

Did anybody please explain me wat is the problem here...
it is showing a null pointer exception...

class array
{
String var;
public static void main(String args[])
    {
    array obj[];
    obj = new array[1];
    obj[0].var="1";
    System.out.println(obj[0].var);
    }
}

friend, why don't you try such this:

class Array
{
    public static void main(String args[])
    {
        String[] obj;
 
        obj = new String[1];
 
            obj[0] = "Hello;
                   System.out.println(obj[0]);    
 
    }
}

[reon]

My dear friend
Try to understand wat i mean , i am calling that variable named ' var ' from the array class...
Think before you post....

friend, why don't you try such this:

class Array
{
    public static void main(String args[])
    {
        String[] obj;
 
        obj = new String[1];
 
            obj[0] = "Hello;
                   System.out.println(obj[0]);    
 
    }
}

[JosAH]

Did anybody please explain me wat is the problem here...
it is showing a null pointer exception...

class array
{
String var;
public static void main(String args[])
    {
    array obj[];
    obj = new array[1];
    obj[0].var="1";
    System.out.println(obj[0].var);
    }
}

When you instantiate an array of type T, as in:

T[] array= new T[42];

... you have created an array of (in this example) 42 references to objects of
type T. They (the references) don't point to anything yet; they are all null.
If you want your references to point to objects of type T you have to make them
do that explicitly as in:

for (int i= 0; i < array.length; i++)
   array[i]= new T(); // point to a new T object

kind regards,

Jos

[reon]

i didnt get you
would you please make it clear,,,

When you instantiate an array of type T, as in:

T[] array= new T[42];

... you have created an array of (in this example) 42 references to objects of
type T. They (the references) don't point to anything yet; they are all null.
If you want your references to point to objects of type T you have to make them
do that explicitly as in:

for (int i= 0; i < array.length; i++)
   array[i]= new T(); // point to a new T object

kind regards,

Jos

[JosAH]

i didnt get you
would you please make it clear,,,

What particular part of my reply didn't you understand?

kind regards,

Jos

[reon]

first of all "When you instantiate an array of type T, as in:"
i didnt understand that .. and how can i slove my prob....

class array
{
String var;
public static void main(String args[])
    {
    array obj[];
    obj = new array[3];
    obj[0].var="A";
    System.out.println(obj[0].var);
    }
}
 

What particular part of my reply didn't you understand?

kind regards,

Jos

[JosAH]

first of all "When you instantiate an array of type T, as in:"
i didnt understand that .. and how can i slove my prob....

T is a type and I want an array of that type, so I create (instantiate) one like this:

T[] array= new T[42];

Now I have an array with 42 references to a type T. These references don't point
to anything yet; you have to do that yourself. In your code you just created the
references (you 'new'd the array) but you didn't make any reference in that
array point to something. You should create an object to point to, as in:

array[0]= new T(); // element 0 of the array now points to a T object

kind regards,

Jos

[reon]

Thanx to all of them who helped me..
I got solution...

But would anybody please explain me that line i commented...

class array
{
String var;
public static void main(String args[])
    {
    array obj[];
    obj = new array[1];
    obj[0]=new array(); // i didnt understand this line...please tell me in details...
    obj[0].var="A";
    System.out.println(obj[0].var);
    }
}
 

[JosAH]

Thanx to all of them who helped me..
I got solution...

But would anybody please explain me that line i commented...

class array
{
String var;
public static void main(String args[])
    {
    array obj[];
    obj = new array[1];
    obj[0]=new array(); // i didnt understand this line...please tell me in details...
    obj[0].var="A";
    System.out.println(obj[0].var);
    }
}
 

That's the line where an object actually is created (by using the 'new' operator).
The reference in the first array slot points to this object now. btw, naming a
user defined type 'array' is very confusing, that's the reason I used the more
abstract type 'T' in my previous replies.

kind regards,

Jos

[reon]

Thanx ..
Is that T abstract type is more easy to understand would you please complete the code for me i didnt understand that(T abstract type) ....
if you demonstrate it with that particular code it might be able to quickly understandable..

That's the line where an object actually is created (by using the 'new' operator).
The reference in the first array slot points to this object now. btw, naming a
user defined type 'array' is very confusing, that's the reason I used the more
abstract type 'T' in my previous replies.

kind regards,

Jos

[JosAH]

Thanx ..
Is that T abstract type is more easy to understand would you please complete the code for me i didnt understand that(T abstract type) ....
if you demonstrate it with that particular code it might be able to quickly understandable..

Ok, a small code snippet can't do much harm:

T[] a; // an array; each element has type T
a= new T[42]; // make an array with 42 T references
a[0]= new T(); // the first element points to a type T object now

kind regards,

Jos