I get these weird characters when I try to print out a vector element!

Question

I\'m using Netbeans. When I run the program below, I get this as output [I@de6ced! How come?

import java.util.Arrays;
import java.util.Vector;

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Answer 1

I think I have figured out what was happening:

 int[] a = new int[1];
 a[0] = 5;

We now have an array of int.

 Vector a1 = new Vector(Arrays.asList(a));

The problem is in the way you are calling Arrays.asList.

The signature for asList is "public static List asList(T... a)". It does not apply with T == int because int is not an object type. And it cannot match with T == Integer because the base type of the array a is int not Integer. What is actually happening is that T is binding to int[], and Arrays.aslist(a) is returning a List with one element that is the value of a!!!

Then you create a Vector from the List and get a Vector with one element ... the original int[] that was assigned to 'a'.

 System.out.println(a1.elementAt(0));

Finally, a1.elementAt(0) fetches the int[], and you end up calling the Object implementation of the toString() method.

A couple of important lesson to learn from this:

• it is a bad idea to mix raw types and generic types as you do on the line that declares a1, and
• it is a bad idea to ignore, or turn off the compiler's generic type-safety warnings