public void makeReadOnly()
  {
    _isReadOnly = true;
  }
@Test(expectedExceptions = UnsupportedOperationException.class)
  public void testMakeReadOnly()
  {
    CompoundKey compoundKey = new CompoundKey();
    compoundKey.append("foo", "foo-value");
    compoundKey.append("bar", 1);
    compoundKey.append("baz", 7L);

    compoundKey.makeReadOnly();

    compoundKey.append("abc", "def");
  }