Java hashCode Tester

HashCodeTester.java

package alluxio;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotEquals;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class HashCodeTester {
  HashMap<Integer, List<Object>> mGroups = new HashMap<>();
  private int mCtr = 0;

  /**
   * Creates a new group of items which should all have equal hash codes but different hash codes
   * from other groups
   * 
   * @param items variable number of objects which should hash to the same value
   * @return this
   */
  HashCodeTester addHashGroup(Object ...items) {
    mGroups.put(mCtr, Arrays.asList(items));
    mCtr++;
    return this;
  }

  /**
   * Tests for equality of hash codes in each group, makes sure there aren't any collisions with
   * items in other groups.
   */
  void testHash() {
    for (Map.Entry<Integer, List<Object>> group: mGroups.entrySet()) {
      int itemNum = 0;
      int hashCode = 0;
      boolean init = false;
      for (Object item : group.getValue()) {
        if (!init) {
          hashCode = item.hashCode();
          init = true;
          itemNum++;
          continue;
        }
        assertEquals(String.format("[group, item] hashCode [%d %d] does not match [%d, %d]",
            group.getKey(), itemNum, group.getKey(), itemNum), item.hashCode(), hashCode);
        for (Map.Entry<Integer, List<Object>> otherGroup : mGroups.entrySet()) {
          if (group.getKey().equals(otherGroup.getKey())) {
            continue;
          }
          int itemCheckNum = 0;
          for (Object checkItem : otherGroup.getValue()) {
            assertNotEquals(String
                    .format("[group, item] hashCode [%d, %d] matches the hash in [%d, %d]",
                        group.getKey(), itemNum, otherGroup.getKey(), itemCheckNum),
                item.hashCode(), checkItem.hashCode());
            itemCheckNum++;
          }
        }
        itemNum++;
      }
    }
  }
}