Generics Question

[Sneha Kapoor]

What will happen when you attempt to compile and run the following code?

 

 import java.util.*;
public class ArrayCon{
    public static void main(String argv[]){
	new ArrayCon();
   }
    ArrayCon(){
	ArrayList <String> al = new ArrayList<String>();
	al.add("apple");
	al.add("orange");
	al.add("mango");
        String[] saFruit =al.toArray(new String[0]); // what does new String[0] contains???
	System.out.print(saFruit[1]);          
	for(String sFruit : saFruit){
	   System.out.print(sFruit); //how come this prints orangemango only
	}
    }
}

Source:- http://www.examulator.com/phezam/

[Chiranjeevi Kanthraj]

System.out.print(sFruit); //how come this prints orangemango only

i'm getting orange apple orange mango

first orange from

System.out.print(saFruit[1]);

what does new String[0] contains???

i dont know

[Henry Wong]

what does new String[0] contains???

The array that was passed is an empty array that the toArray() method will use only to determine the type (because the result to be return couldn't fit). In this example, a new array of the same type, but larger, is returned.

Henry

[Chiranjeevi Kanthraj]

what does new String[0] contains???

Which tells the toArray() method to give in String array format
String[0] means you telling to put in the String array with 0 elements, but ArrayList has 3 elements so it will append to the String[0].
If you need to see the difference make that String[0] to more the 3 means more then elements which ArrayList has you will get like below

   orangeappleorangemangonullnullnullnullnull  

means it will add null to left over array elements.

i think i catch this.

[deepesh soni]

al.toArray(new String[0]) works like al.toArray() function if the list contain only String objects

[Henry Wong]

Chiranjeevi Kanthraj wrote:
String[0] means you telling to put in the String array with 0 elements, but ArrayList has 3 elements so it will append to the String[0].

Actually, no. It won't append to the array -- Java arrays can't change in size. The method will instantiate a new array of the same type.

Chiranjeevi Kanthraj wrote:
If you need to see the difference make that String[0] to more the 3 means more then elements which ArrayList has you will get like below

   orangeappleorangemangonullnullnullnullnull  

means it will add null to left over array elements.

When you pass in an array that can fit the data -- it will simply use it, and ignore any leftover array elements. The reason the left over array elements were null, is because they were null when you intantiated the array. The toArray() method didn't add any nulls.

Henry