test/jdk/java/util/HashMap/NullKeyAtResize.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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/**
 * @test
 * @bug 7173432
 * @summary If the key to be inserted into a HashMap is null and the table
 * needs to be resized as part of the insertion then addEntry will try to
 * recalculate the hash of a null key. This will fail with an NPE.
 */

import java.util.*;

public class NullKeyAtResize {
    public static void main(String[] args) throws Exception {
        List<Object> old_order = new ArrayList<>();
        Map<Object,Object> m = new HashMap<>(16);
        int number = 0;
        while(number < 100000) {
            m.put(null,null); // try to put in null. This may cause resize.
            m.remove(null); // remove it.
            Integer adding = (number += 100);
            m.put(adding, null); // try to put in a number. This wont cause resize.
            List<Object> new_order = new ArrayList<>();
            new_order.addAll(m.keySet());
            new_order.remove(adding);
            if(!old_order.equals(new_order)) {
                // we resized and didn't crash.
                System.out.println("Encountered resize after " + (number / 100) + " iterations");
                break;
            }
            // remember this order for the next time around.
            old_order.clear();
            old_order.addAll(m.keySet());
        }
        if(number == 100000) {
            throw new Error("Resize never occurred");
        }
    }
}