int[] = null; help

[adeeb alexander]

Hi all.
As normal how we declare a string array when we dont know the size i.e how much data should be inserted then i give as String[] str = null. After that i can perform all the operations. When i try to do the same with int that is int[] arr = null. I dont get compilation error, when i try to access its elements i am getting the java.nullpointer exception.



Any help would be greatly appreciated.
Thanks
alexander

[Greg Charles]

I'm not sure I understand. If you set something to null, then try to access it, of course you will get a null pointer exception. In your first example, with the String array, the same thing would happen.

[Mamata Chaudhari]

hi..
If you want dynamic size then you can use ArrayList<String>

but it is not possible to define string array without size.

[adeeb alexander]

Thanks for your replies guyz. See the code below. I declared a String[] temp and used it like this below. It works for me.

   
String[] temp=null;
					while((str = br.readLine())!=null)
					{
						temp=str.split("::");
						
						fileCol.addElement(temp[0]);
						alpha.addElement(temp[1]);
						colSize.addElement(temp[2]);
					} 

[Rob Spoor]

That's because your giving it a value first, on line 5.

[adeeb alexander]

yes. In the same way i have given values for int[] also. For example consider.
int [] exp= null;
for(int i = 0;i<5;i++);
{
exp[i]=i;
}

I have to do somewhat this thing in my program also.

when i use System.out.println(exp[0]);

i get error during execution. i need the reason please. As you said i have given values to exp isnt it?


Thanks

[Rob Spoor]

You don't assign anything to exp itself. Nowhere are you calling "exp = X" where X is something other than null. That means that the array itself remains null, and there are no elements to access.

With the String[] you are doing just that and that's why that example is working and this one isn't.

The easiest solution is adding "exp = new int[5];" just before the loop.

[adeeb alexander]

Hi
Look at the code below. I am using this to solve given input separated by ",". I think i have used some extra code. i.e i guess there is some other short way to do this. If any one know please share with me.

  import java.io.*;

public class Test
{
	public static void main(String args[])
	{
		try
		{
			BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
			String input = br.readLine();
			String[] temp = input.split("\\s?+,\\s?+");
			int[] cr = new int[temp.length];
			for(int i=0;i<temp.length;i++)
			{
				cr[i]=Integer.parseInt(temp[i]);
				System.out.println(cr[i]);				
			}
			
		}
		catch(Exception ce)
		{
			System.out.println(ce);
		}
	}
}  

Thanks and Regards
alexander
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