Bug 133375 [Viewers] Need access to the element comparer of a tree selection
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CustomHashtable.java
private HashMapEntry getEntry(Object key) {
        int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
        HashMapEntry entry = elementData[index];
        while (entry != null) {
            if (keyEquals(key, entry.key)) {
				return entry;
			}
            entry = entry.next;
        }
        return null;
    }
    /**
     * Answers the hash code for the given key.
     */
    private int hashCode(Object key) {
        if (comparer == null) {
			return key.hashCode();
		} else {
			return comparer.hashCode(key);
		}
    }
    /**
     * Compares two keys for equality.
     */
    private boolean keyEquals(Object a, Object b) {
        if (comparer == null) {
			return a.equals(b);
		} else {
			return comparer.equals(a, b);
		}