What are Conditional Writes in AWS DynamoDB

@Configuration
public class DynamoConfig {
    private static final Logger logger = LoggerFactory.getLogger(DynamoConfig.class);

    @Bean
    AmazonDynamoDBClient dbClient(@Value("${aws.dynamodb.endpoint}") String amazonDynamoDBEndpoint, AWSSettings awsSettings) {
        AmazonDynamoDBClient dbClient = new AmazonDynamoDBClient(
                new BasicAWSCredentials(awsSettings.getAccessKey(), awsSettings.getSecretKey()));
        dbClient.setRegion(Region.getRegion(Regions.fromName(awsSettings.getRegion())));
        logger.info("DB Endpoint is " + amazonDynamoDBEndpoint);
        if (!StringUtils.isEmpty(amazonDynamoDBEndpoint)) {
            dbClient.setEndpoint(amazonDynamoDBEndpoint);
        }
        if (awsSettings.getRegion().equalsIgnoreCase("local")) {
            dbClient.setEndpoint("http://localhost:8000");
        }
        return dbClient;
    }

    @Bean
    DynamoDB dynamoDB(AmazonDynamoDBClient client) {
        return new DynamoDB(client);
    }
}

public void incrementViewsUsingConditionalExpression(String contentId, long newValue, long expected) {
    Table table = dynamoDB.getTable("local-content");
    UpdateItemSpec updateItemSpec = new UpdateItemSpec()
            .withPrimaryKey("id", contentId)
            .withUpdateExpression("SET #fn = :newval")
            .withConditionExpression("#fn = :currval")
            .withNameMap(new NameMap()
                    .with("#fn", "views")
            )
            .withValueMap(new ValueMap()
                    .withNumber(":newval", newValue)
                    .withNumber(":currval", expected)
            )
            .withReturnValues(ReturnValue.ALL_NEW);

    UpdateItemOutcome outcome = table.updateItem(updateItemSpec);
    System.out.println(outcome.getItem().toJSONPretty());
}