shuffle loses/duplicates objects in LinkedList
From: Adrian Collister (aac27_at_cam.ac.uk)
Date: 01/19/05
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Date: Wed, 19 Jan 2005 19:51:55 +0000
I'm trying to use the Collections.shuffle() method on a LinkedList. After
the shuffle() the LinkedList is totally mangled, with several of the
original Objects being replaced by duplicates of others. If I use an
ArrayList instead of the LinkedList the behaviour is as expected.
Am I doing something wrong, or is this a bug?
The appended code demonstrates the problem. Example output when I execute
it:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
0 3 7 0 6 13 4 1 12 15 11 6 14 2 7 3 17 14 17 8
0 0 1 2 3 3 4 6 6 7 7 8 11 12 13 14 14 15 17 17
I'm using the GCC java compiler - might be interesting to see what happens
if it's compiled using Sun's compiler.
Adrian
/*---------------- CODE -----------------*/
import java.util.List;
import java.util.LinkedList;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Collections;
public class ShuffleTest
{
public static void main(String[] args)
{
// Fill a list with "Int" objects (see below)
LinkedList x = new LinkedList();
for (int i = 0; i < 20; ++i) {
x.add(new Int(i));
}
// Shuffle then re-sort...
printList(x);
Collections.shuffle(x);
printList(x);
Collections.sort(x);
printList(x);
}
// Dump list to STDOUT.
public static void printList(List l)
{
Iterator it = l.iterator();
while (it.hasNext()) {
System.out.print(((Int)it.next()).value + " ");
}
System.out.println();
}
// Simple Class which just contains an int.
public class Int implements Comparable
{
int value;
// Constructor
public Int(int v)
{
this.value = v;
}
public int compareTo(Object o)
{
Int i = (Int) o;
if (value < i.value) {
return -1;
} else if (value == i.value) {
return 0;
} else {
return 1;
}
}
}
}
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