doubt in List.indexOf()

[Fissehaye Kahsay]

Hi ranchers
why are the two outputs in the following code -1(unfound). As you can see, there is 4 in the array and I created a list using Array.asList()

   
import java.util.*;
public class BeforeFour {
    public static void main(String[] args) {
        BeforeFour b = new BeforeFour();
        List list;
        int length;
        int length2;
        int[] i = {1,2,3,4,5,6,7,8,9};
        list = Arrays.asList(i);
        length = list.indexOf(new Integer(4));
        length2 = list.indexOf(4);
 
        System.out.println(length);
        System.out.println(length2);
    }
}
 

[Evan Caballero]

here it is :

public static void main(String[] args) {
		List list;
		int length;
		int length2;
		Integer[] i = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
		list = Arrays.asList(i);
		length = list.indexOf(new Integer(4));
		length2 = list.indexOf(4);

		System.out.println(length);
		System.out.println(length2);
	}

I think that when the JVM autoboxes int to Integer, the Integer.equals() method is ignored or something like that.

[William Brogden]

Looks like the indexOf is using identity of the reference, not the content of the object.

Bill

[Fissehaye Kahsay]

thanks for your help
but how can I get the index of 4 in the int[] not in Integer[] ?. I'm forced to use the int[] instead of Integer[] (just calling a method which takes int[])

[Evan Caballero]

In fact, when you do i.asList(), it returns a list of int[] (List<int[]>) with one element :/

like [{ 1, 2, 3, 4, 5, 6, 7, 8, 9 }]

so, there is no element at index 4 ; there is only an element at index 0, which is your original int[].

the asList method considers that you want to build a list from one int[], which IS an object. It is like if you were doing Arrays.asList(i1, i2, i3, i4), where i1 i2 i3 and i4 are int[] objects.

[Rob Spoor]

Evan is right. Arrays.asList will only work on objects, not on primitives. You will need to box the entire array - convert each element into Integer objects first. You may want to switch to a "regular" List implementation:

int[] i = {1,2,3,4,5,6,7,8,9};   
//list = Arrays.asList(i); 
list = new ArrayList<Integer>(i.length);
for (int j: i)
{
    list.add(j);
}