Re: how to write array elements to console

From:
"Oliver Wong" <owong@castortech.com>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 13 Dec 2006 10:19:14 -0500
Message-ID:
<URUfh.66743$aJ6.652232@wagner.videotron.net>
"Dzikus" <dzikus_@vp.pl> wrote in message
news:1166003160.908230.256520@80g2000cwy.googlegroups.com...

Hello,
I have following problem:
Let's assume there is a function
  f(Object obj){
  ...
  }
And if obj is an array (of some primitive types) I want to write
elements to Sysytem.out

For example if I have:
int[] array = {1, 2, 3, 4};
f(array);

The expected result would be
1
2
3
4
Does anybody knows how to do it?


    Here's a solution that does not do any downcasting, nor use any switch
statement. However, it does use an exception for control flow, which is
somewhat frowned upon.

<SSCCE>
import java.lang.reflect.Array;

public class ArrayTest {
 public static void main(String[] args) {
  f(new int[] { 1, 2, 3 });
  f(new byte[] { 4, 5, 6 });
  f(new char[] { 'a', 'b', 'c' });
 }

 public static void f(Object o) throws IllegalArgumentException {
  if (!o.getClass().isArray()) {
   throw new IllegalArgumentException("Not an array.");
  }
  int index = 0;
  try {
   while (true) {
    System.out.println(Array.get(o, index));
    index++;
   }
  }
  catch (ArrayIndexOutOfBoundsException aioobe) {
   // do nothing
  }
 }
}

</SSCCE>

The issue is that I can't figure out how to get the length of the array
without performing a cast. The following does not work:

o.getClass().getField("length").getInt(o);

It throws a NoSuchFieldException, which surprises me, because I'm pretty
sure arrays have a field called "length". But maybe it has to do with the
fact that arrays are somewhat "magical" and not pure objects?

    - Oliver

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