IBM Cloud Authors: Yeshim Deniz, Liz McMillan, Pat Romanski, Elizabeth White, Karthick Viswanathan

Related Topics: IBM Cloud, Java IoT, Adobe Flex, Open Source Cloud, Eclipse, Machine Learning

IBM Cloud: Article

Reflections on Java Command Line Options

There are many different types of command line options that programs need to recognize

There are many different types of command line options that programs need to recognize. Many languages (e.g.: bash and perl) has built-in processing of command line options; Java does not. The Java Command Line Options (JCLO) package performs this task for a variety of option styles. It also uses Java's reflection capability to automatically assign values to variables in a specified class.

Even in these days of sophisticated graphical user interfaces, many programs have a wide variety of command line options that help specify their behavior. It is also the case that command line only programs continue to enjoy wide use. It is also the case the command line arguments can become quite complicated, e.g.: -Djava.util.logging.config.file=All.finest -1 --list --this=that Some languages have built-in parsers for command line options; perl and bash are two obvious examples of this. Java has no such parser built in. The JCLO package provides the capability to parse several different command line option formats, and uses Java's reflecion mechanizm to both drive the parsing and assign the values provided by command line options to the variable in a specified class.

Brief overview of command line option formats
UNIX command line options started with a simple "dash and letter" format. "ls -l" is a classic example. If the option specified an additional option, the dash and letter were followed by a space and the additional option. "sort -t separator" is and example. UNIX also allowed the use of numbers, "ls -1", as options. As the number of possible option proliferated, and newer "GNU" style was developed. These have a "double dash/long name" style: "sort --version" for example. When additional options are needed for this style, it is typically provided with a "equals value" style: "gcc --std=c89". Finally, Java has its own style of "single dash/name with dots/equals value" style: "-Djava.util.logging.config.file=logging.props".

Specifying non-Java variable name options
JCLO uses Java reflection to extract variable names as the basis for parsing command line options. Not all styles just described are valid Java variable names and therefore JCLO uses several conventions to allow them specified. Java variables must begin with an alphabetic character or an underscore, numbers are not allowed to start a variable name. Variable names cannot contain dashes, as dashes specify subtraction or negation. They cannot contain dots as dots specify class references or decimal literals. Therefore, JCLO uses the convention of prefixing number options with an underscore (_1). For dashes embedded in options (e.g.: "--font-size=10"), JCLO uses two underscores ("font__size") in the variable name. For the embedded dots, JCLO uses a convention of an underscore followed by a dollar sign "_$".

Brief review of Java reflection
Java, as with other object oriented languages, has the ability to query and modify an object's internal information. One can retrieve a Class's constructors, methods, fields, etc. JCLO uses the getDeclaredFields()" method on a class to find the names it will accept and set the value for. One can either have a single class devoted to command line options or specify a prefix for the variables JCLO's will examine.

From class variables to command line options
First let's look at an example to see how JCLO works in practice. We have the obligatory import:

import edu.mscd.cs.jclo.JCLO;

and then we create a class whose class varibles will become the command line options:

class ExampleArgs
    private int a;
    private boolean b;
    private float c;
    private String d;
    private String[] additional;

A simple main will be used to illustrate JCLO's operation:

public class Example
    public static void main (String args[])
        ExampleArgs ea = new ExampleArgs();
        JCLO jclo = new JCLO (ea);
        jclo.parse (args);
	System.out.println ("a = " + ea.a);
	System.out.println ("b = " + ea.b);
	System.out.println ("c = " + ea.c);
	System.out.println ("d = " + ea.d);
	System.out.println ("additional = " + 
	    java.util.Arrays.toString (ea.additional));

First, an object that contains the variables whose values will be assigned by the command line options is created. This object is then used to create a JCLO object. The parse method is then called with the command line options to do the actual work Running this simple program with the following command line options:

java -cp .:JCLO-1.3.4.jar Example -a 5 --b=true --c=9.0 -d Example one two three


a = 5
b = true
c = 9.0
d = Example
additional = [one, two, three]

Here, each of the class varibles where assigned values from the associated command line option. The additional String array is assigned any options beyond the last dash option. JCLO can also use only certain fields of an object by the programmer specifying a string prefix that those fields begin with.

There are times when command line options have aliases; for example a long and short version. JCLO has the ability to deal with these directly. Adding

String aliases[][] ={{"boolean", "b"}};

and modifying

JCLO jclo = new JCLO (ea, aliases);

to the above example allows for --boolean to set the value for b


java -cp .:JCLO-1.3.4.jar Example --boolean
a = 0
b = true
c = 0.0
d = null
additional = null

JCLO also has a simple usage() method that returns a String of possible options and the type of values they require.

JCLO allows one to easily parse command line options and set the values inside a class based on those options. It is very flexible in its parsing, allowing intermixed single- and double-dashed options, along with aliases that allow long and short versions of an option. JCLO is available from http://jclo.sourceforge.net/.

More Stories By Steve Beaty

Steve has an extensive background in both the theoretic and pragmatic aspects of computer science. He wrote compilers at Cray Computer, and both managed a large group of developers and was a software test architect at HP. He has a number of active open-source projects and is a professor of computer science at the Metropolitan State College of Denver.

@ThingsExpo Stories
DevOpsSummit New York 2018, colocated with CloudEXPO | DXWorldEXPO New York 2018 will be held November 11-13, 2018, in New York City. Digital Transformation (DX) is a major focus with the introduction of DXWorldEXPO within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of bus...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
DXWorldEXPO LLC announced today that ICOHOLDER named "Media Sponsor" of Miami Blockchain Event by FinTechEXPO. ICOHOLDER give you detailed information and help the community to invest in the trusty projects. Miami Blockchain Event by FinTechEXPO has opened its Call for Papers. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to info@dxworldexpo.com. Miami Blockchain Event by FinTechEXPO also offers s...
DXWorldEXPO | CloudEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
Cloud-enabled transformation has evolved from cost saving measure to business innovation strategy -- one that combines the cloud with cognitive capabilities to drive market disruption. Learn how you can achieve the insight and agility you need to gain a competitive advantage. Industry-acclaimed CTO and cloud expert, Shankar Kalyana presents. Only the most exceptional IBMers are appointed with the rare distinction of IBM Fellow, the highest technical honor in the company. Shankar has also receive...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities - ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups.
Poor data quality and analytics drive down business value. In fact, Gartner estimated that the average financial impact of poor data quality on organizations is $9.7 million per year. But bad data is much more than a cost center. By eroding trust in information, analytics and the business decisions based on these, it is a serious impediment to digital transformation.
Predicting the future has never been more challenging - not because of the lack of data but because of the flood of ungoverned and risk laden information. Microsoft states that 2.5 exabytes of data are created every day. Expectations and reliance on data are being pushed to the limits, as demands around hybrid options continue to grow.
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
As IoT continues to increase momentum, so does the associated risk. Secure Device Lifecycle Management (DLM) is ranked as one of the most important technology areas of IoT. Driving this trend is the realization that secure support for IoT devices provides companies the ability to deliver high-quality, reliable, secure offerings faster, create new revenue streams, and reduce support costs, all while building a competitive advantage in their markets. In this session, we will use customer use cases...
Business professionals no longer wonder if they'll migrate to the cloud; it's now a matter of when. The cloud environment has proved to be a major force in transitioning to an agile business model that enables quick decisions and fast implementation that solidify customer relationships. And when the cloud is combined with the power of cognitive computing, it drives innovation and transformation that achieves astounding competitive advantage.
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, @CloudEXPO and DXWorldEXPO are two of the most important technology events of the year. Since its launch over eight years ago, @CloudEXPO and DXWorldEXPO have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, we provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading...
The best way to leverage your Cloud Expo presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering Cloud Expo and @ThingsExpo will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at Cloud Expo. Product announcements during our show provide your company with the most reach through our targeted audiences.
The IoT Will Grow: In what might be the most obvious prediction of the decade, the IoT will continue to expand next year, with more and more devices coming online every single day. What isn’t so obvious about this prediction: where that growth will occur. The retail, healthcare, and industrial/supply chain industries will likely see the greatest growth. Forrester Research has predicted the IoT will become “the backbone” of customer value as it continues to grow. It is no surprise that retail is ...
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...
DXWorldEXPO LLC announced today that "Miami Blockchain Event by FinTechEXPO" has announced that its Call for Papers is now open. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to info@dxworldexpo.com. Financial enterprises in New York City, London, Singapore, and other world financial capitals are embracing a new generation of smart, automated FinTech that eliminates many cumbersome, slow, and expe...