Can a Java map return a size of -1?

Question

I have code that creates a List initialized with map size:

private Set<String> mKeys = new HashSet<String>(64);
....
List<String> keyList = new ArrayList<String>(mKeys.size());

I see an exception: java.lang.IllegalArgumentException: Invalid capacity: -1

Can a card return a size of -1? I am looking at the source code for a HashSet that is supported by HashMap. The source code for the HashMap shows the insides where elementCount is always reduced by a call to removeEntry (). In addition, the HashMap.empty () response methods to elementCount are == 0, which return false if elementCount is -1.

Has anyone come across this before? I can encode it, but it seems like a hack, which makes me think that I am doing something wrong with the current code.

EDIT: I tried to simplify the task first. The set that I use is actually defined as

private static Set<String> mKeys = Collections.synchronizedSet(new HashSet<String>(64));

EDIT: synchronizedSet. JavaDoc:

, :

Set s = Collections.synchronizedSet(new HashSet());
      ...
synchronized(s) {
    Iterator i = s.iterator(); // Must be in the synchronized block
    while (i.hasNext())
        foo(i.next());
}

.

-1. , , , .

Answer 1

, HashMap , - . .

, , Integer.MAX_VALUE + 1, . AbstractMap # size() , Integer.MAX_VALUE, Integer.MAX_VALUE, .

, :

Set<String> mKeys = new HashSet<String>(64);
System.out.println(mKeys.size());

: 0.

, "...." ?

Answer 2

hashSet size() . 1 , . 2 - - , , .

Edit: .. Java 1.6 . Java 1.7 HashSet . , HashSet.

1

package test;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

class TestHashSet1 {
    private static int NUMBER_OF_THREADS = 5;
    private static int COLLECTION_SIZE = 1000;

    public static void main(String[] arg) {
        final Set<Integer> toRemoveElement = new HashSet<Integer>();
        final Set<Integer> toStoreElements = new HashSet<Integer>();
        // populate collections for test
        for (int i = 0; i < COLLECTION_SIZE; i++) {
            Integer obj = new Integer(i);
            toRemoveElement.add(obj);
            toStoreElements.add(obj);
        }
        // two threads that will be using collection2 
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                for (Integer o : toStoreElements) {
                    removeObject(toRemoveElement, o);
                }
            }
        };
        Thread[] treads = new Thread[NUMBER_OF_THREADS];
        for (int i = 0; i < treads.length; i++) {
            treads[i] = new Thread(runnable);
        }
        for (Thread t : treads) {
            t.start();
        }
    }

    private static void removeObject(Set<Integer> toRemoveElement, Integer o) {
        toRemoveElement.remove(o);
        int size = toRemoveElement.size();
        if (size < 0) {
            System.out.println(size);
            try {
                toRemoveElement.toArray(new Integer[toRemoveElement.size()]);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

2 -

package test;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

class TestHashSet2 {
    private static int NUMBER_OF_THREADS = 5;
    private static int COLLECTION_SIZE = 1000;

    public static void main(String[] arg) {
        final Set<Integer> toRemoveElement = Collections.synchronizedSet(new HashSet<Integer>()); // example of collection sync
        final Set<Integer> toStoreElements = new HashSet<Integer>();
        // populate collections for test
        for (int i = 0; i < COLLECTION_SIZE; i++) {
            Integer obj = new Integer(i);
            toRemoveElement.add(obj);
            toStoreElements.add(obj);
        }
        // two threads that will be using collection2 
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                for (Integer o : toStoreElements) {
                    removeObject(toRemoveElement, o);
                }
            }
        };
        Thread[] treads = new Thread[NUMBER_OF_THREADS];
        for (int i = 0; i < treads.length; i++) {
            treads[i] = new Thread(runnable);
        }
        for (Thread t : treads) {
            t.start();
        }
    }

    synchronized private static void removeObject(Set<Integer> toRemoveElement, Integer o) { // example of method sync
        toRemoveElement.remove(o);
        int size = toRemoveElement.size();
        if (size < 0) {
            System.out.println(size);
            try {
                toRemoveElement.toArray(new Integer[toRemoveElement.size()]);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

Answer 3

HashMap () -1. size() , HashMap, , ( (NB not LinkedList)). , , , (, Integer.MAX_VALUES). , .