### Question:
StructureDB extends CompositeDB implements Structure { @Override public DataTypeComponent replace(int ordinal, DataType dataType, int length, String name, String comment) throws IllegalArgumentException { lock.acquire(); try { checkDeleted(); if (ordinal < 0 || ordinal >= numComponents) { throw new ArrayIndexOutOfBoundsException(ordinal); } validateDataType(dataType); DataTypeComponent origDtc = getComponent(ordinal); if (origDtc.isBitFieldComponent()) { throw new IllegalArgumentException( "Bit-field component may not be directly replaced"); } if (dataType == DataType.DEFAULT) { clearComponent(ordinal); return getComponent(ordinal); } dataType = resolve(dataType); checkAncestry(dataType); length = getPreferredComponentLength(dataType, length); DataTypeComponent replaceComponent = replaceComponent(origDtc, dataType, length, name, comment, true); adjustInternalAlignment(true); return replaceComponent; } catch (DataTypeDependencyException e) { throw new IllegalArgumentException(e.getMessage(), e); } finally { lock.release(); } } StructureDB(DataTypeManagerDB dataMgr, DBObjectCache<DataTypeDB> cache,
			CompositeDBAdapter compositeAdapter, ComponentDBAdapter componentAdapter,
			Record record); @Override String getRepresentation(MemBuffer buf, Settings settings, int length); @Override DataTypeComponent add(DataType dataType, int length, String name, String comment); @Override void growStructure(int amount); @Override DataTypeComponent insert(int ordinal, DataType dataType, int length, String name,
			String comment); @Override DataTypeComponent addBitField(DataType baseDataType, int bitSize, String componentName,
			String comment); @Override DataTypeComponent insertBitField(int ordinal, int byteWidth, int bitOffset,
			DataType baseDataType, int bitSize, String componentName, String comment); @Override DataTypeComponent insertBitFieldAt(int byteOffset, int byteWidth, int bitOffset,
			DataType baseDataType, int bitSize, String componentName, String comment); @Override void delete(int ordinal); @Override void delete(int[] ordinals); @Override boolean isPartOf(DataType dataType); @Override int getNumComponents(); @Override int getNumDefinedComponents(); @Override DataTypeComponent getComponent(int ordinal); @Override DataTypeComponent[] getComponents(); @Override DataType copy(DataTypeManager dtm); @Override Structure clone(DataTypeManager dtm); @Override boolean isNotYetDefined(); @Override int getAlignment(); @Override int getLength(); @Override void clearComponent(int ordinal); @Override void deleteAtOffset(int offset); @Override DataTypeComponent getComponentAt(int offset); @Override DataTypeComponent getDataTypeAt(int offset); @Override DataTypeComponentDB[] getDefinedComponents(); @Override final DataTypeComponent insertAtOffset(int offset, DataType dataType, int length); @Override DataTypeComponent insertAtOffset(int offset, DataType dataType, int length, String name,
			String comment); @Override DataTypeComponent replace(int ordinal, DataType dataType, int length, String name,
			String comment); @Override final DataTypeComponent replace(int ordinal, DataType dataType, int length); @Override DataTypeComponent replaceAtOffset(int offset, DataType dataType, int length, String name,
			String comment); @Override void replaceWith(DataType dataType); @Override void dataTypeDeleted(DataType dt); @Override void dataTypeSizeChanged(DataType dt); @Override void dataTypeAlignmentChanged(DataType dt); @Override boolean isEquivalent(DataType dataType); @Override String getDefaultLabelPrefix(); @Override void dataTypeReplaced(DataType oldDt, DataType newDt); @Override void dataTypeNameChanged(DataType dt, String oldName); @Override void deleteAll(); @Override void realign(); @Override void pack(int packingSize); @Override boolean hasFlexibleArrayComponent(); @Override DataTypeComponentDB getFlexibleArrayComponent(); @Override DataTypeComponent setFlexibleArrayComponent(DataType flexType, String name,
			String comment); @Override void clearFlexibleArrayComponent();  }### Answer:
@Test public void testReplaceFailure() { DataTypeComponent dtc = null; try { dtc = struct.replace(0, new QWordDataType(), 8); } catch (IllegalArgumentException e) { } assertNull(dtc); }