final FieldMetadataBuilder fieldBuilder = new FieldMetadataBuilder(
SIMPLE_CLASS_DECLARED_BY_MID, Modifier.PRIVATE,
new JavaSymbolName("newFieldAddedByCode"), new JavaType(
String.class), "\"Create by code\"");
final ClassOrInterfaceTypeDetails newSimpleInterfaceDetails = addField(
simpleInterfaceDetails, fieldBuilder.build());
// Invoke
final String result = typeParsingService
.updateAndGetCompilationUnitContents(file.getCanonicalPath(),
newSimpleInterfaceDetails);