### Question:
Roaring64Bitmap implements Externalizable, LongBitmapDataProvider { public void flip(final long x) { byte[] high = LongUtils.highPart(x); ContainerWithIndex containerWithIndex = highLowContainer.searchContainer(high); if (containerWithIndex == null) { addLong(x); } else { char low = LongUtils.lowPart(x); Container freshOne = containerWithIndex.getContainer().flip(low); highLowContainer.replaceContainer(containerWithIndex.getContainerIdx(), freshOne); } } Roaring64Bitmap(); void addInt(int x); @Override void addLong(long x); @Override long getLongCardinality(); int getIntCardinality(); @Override long select(final long j); Iterator<Long> iterator(); @Override void forEach(final LongConsumer lc); @Override long rankLong(long id); void or(final Roaring64Bitmap x2); void xor(final Roaring64Bitmap x2); void and(final Roaring64Bitmap x2); void andNot(final Roaring64Bitmap x2); @Override void writeExternal(ObjectOutput out); @Override void readExternal(ObjectInput in); @Override String toString(); @Override LongIterator getLongIterator(); @Override boolean contains(long x); @Override int getSizeInBytes(); @Override long getLongSizeInBytes(); @Override boolean isEmpty(); @Override ImmutableLongBitmapDataProvider limit(long x); boolean runOptimize(); @Override void serialize(DataOutput out); void serialize(ByteBuffer byteBuffer); void deserialize(DataInput in); void deserialize(ByteBuffer in); @Override long serializedSizeInBytes(); void clear(); @Override long[] toArray(); static Roaring64Bitmap bitmapOf(final long... dat); void add(long... dat); void add(final long rangeStart, final long rangeEnd); @Override LongIterator getReverseLongIterator(); @Override void removeLong(long x); @Override void trim(); @Override int hashCode(); @Override boolean equals(Object obj); void flip(final long x); @Override Roaring64Bitmap clone();  }### Answer:
@Test public void testFlip() { Roaring64Bitmap map = newDefaultCtor(); map.addLong(0); map.flip(0); assertFalse(map.contains(0)); assertTrue(map.getLongCardinality() == 0); }