Welcome!

Java IoT Authors: Pat Romanski, Elizabeth White, Liz McMillan, Yeshim Deniz, Amit Gupta

Related Topics: Java IoT

Java IoT: Blog Feed Post

A Quick Introduction to the Groovy Language (Part 1)

Groovy is a general purpose scripting language that runs on the JVM

Before I start talking about using Groovy's capabilities to create a DSL (mostly in Java), let's take a few minutes to go over what Groovy is.

Groovy is a general purpose scripting language which runs on the JVM, and can largely be viewed as a superset of Java.  Take the following program:

public class Hello {

    String name;
    
    public void sayHello() {
        System.out.println("Hello "+getName()+"!");
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
    
    public static void main(String[] args) {
    
        Hello hello = new Hello();
        hello.setName("world");
        hello.sayHello();
    }
}

Is this a Groovy program or a Java program?  Yes, it is - it will compile and run in both.  This basic program is a bit wordy, and we can certainly do things more simply in Java, but this contains a number of patterns that you'd commonly see, including the use of the bean pattern, as well as the use of the main method to make the class executable via the java command line program.    When we run it, it simply prints out "Hello world!", as is customary in these sorts of things.

To try this out in Java, you can use your favorite IDE.  You can also use an IDE to try this in Groovy, but you may just want to use the groovyConsole program, which is available as part of the GDK.  Download it now, and play along via cut and paste...

Now, as I said, Groovy is a rough superset of Java - one difference is that things are public by default.  That means we could just as easily say the following:

class Hello {

    String name;
    
    void sayHello() {
        System.out.println("Hello "+getName()+"!");
    }
    
    void setName(String name) {
        this.name = name;
    }
    
    String getName() {
        return name;
    }
    
    static void main(String[] args) {
    
        Hello hello = new Hello();
        hello.setName("world");
        hello.sayHello();
    }
}

Accessors and mutators are automatically created for your class variables, so we can also shorten it by taking those out:

class Hello {

    String name;
    
    void sayHello() {
        System.out.println("Hello "+getName()+"!");
    }
    
    static void main(String[] args) {
    
        Hello hello = new Hello();
        hello.setName("world");
        hello.sayHello();
    }
}

Now we're getting somewhere.  In Groovy, System.out.println can be shortened to just "println" as a convenience, so you can also say:

class Hello {

    String name;
    
    void sayHello() {
        println("Hello "+getName()+"!");
    }
    
    static void main(String[] args) {
    
        Hello hello = new Hello();
        hello.setName("world");
        hello.sayHello();
    }
}

There's also a difference in how Groovy deals with String objects - double quote strings allow for variable substitution.  There's also single quote strings, which do not:

class Hello {

    String name;
    
    void sayHello() {
        println("Hello $name!");
    }
    
    static void main(String[] args) {
    
        Hello hello = new Hello();
        hello.setName('world');
        hello.sayHello();
    }
}

Groovy also allows dot notation to get and set fields of classes, just like Java.  Unlike Java, this will actually go through the getter/setter methods (which, you'll recall, are automatically generated in our current example):

class Hello {

    String name;
    
    void sayHello() {
        println("Hello $name!");
    }
    
    static void main(String[] args) {
    
        Hello hello = new Hello();
        hello.name = 'world';
        hello.sayHello();
    }
}

Typing information is also optional - instead of specifying a type, you can just use the keyword def.  Use of def is mandatory for methods, but optional for parameters on those methods.  You should also use def for class and method variables.  While we're at it, let's take out those semicolons:  They're optional in Groovy.

class Hello {

    def sayHello(name) {
        println("Hello $name!")
    }
    
    static def main(args) {
        Hello hello = new Hello()
        def name = 'world'
        hello.sayHello(name)
    }
}

OK, that's nice, but we can get this even shorter. Because Groovy is a scripting language, there's automatically a wrapping class (called Script, which will become very important to us later). This wrapping class means that we can get rid of our own wrapping class, as well as the main method, like so:

def sayHello(name) {
    println("Hello $name!")
}
def name = 'world'
sayHello(name)

That's all for now, I'll do a second part to this later.  But for now, if someone asks you if you know Groovy, you can now say "Sure, a bit".

Credit for the idea behind this post goes to Guillaume Laforge - I saw him give a variation of this as an intro to his talk at JavaOne, and loved it.

(As usual, this article is cross posted on my main blog site.)

Read the original blog entry...

More Stories By Jim Driscoll

Jim Driscoll has worked at Sun Microsystems for 12 years, working on such projects as the first version of Servlets (in the Java Web Server), and the initial implementation of Java 2, Enterprise Edition. He is currently a Senior Engineer working on the implementation of Java Server Faces, helping to integrate technologies such as AJAX and Comet into the new release.

@ThingsExpo Stories
SYS-CON Events announced today that SourceForge has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. SourceForge is the largest, most trusted destination for Open Source Software development, collaboration, discovery and download on the web serving over 32 million viewers, 150 million downloads and over 460,000 active development projects each and every month.
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. As a result, many firms employ new business models that place enormous impor...
SYS-CON Events announced today that TidalScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale is the leading provider of Software-Defined Servers that bring flexibility to modern data centers by right-sizing servers on the fly to fit any data set or workload. TidalScale’s award-winning inverse hypervisor technology combines multiple commodity servers (including their ass...
As popularity of the smart home is growing and continues to go mainstream, technological factors play a greater role. The IoT protocol houses the interoperability battery consumption, security, and configuration of a smart home device, and it can be difficult for companies to choose the right kind for their product. For both DIY and professionally installed smart homes, developers need to consider each of these elements for their product to be successful in the market and current smart homes.
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, will lead you through the exciting evolution of the cloud. He'll look at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering ...
As hybrid cloud becomes the de-facto standard mode of operation for most enterprises, new challenges arise on how to efficiently and economically share data across environments. In his session at 21st Cloud Expo, Dr. Allon Cohen, VP of Product at Elastifile, will explore new techniques and best practices that help enterprise IT benefit from the advantages of hybrid cloud environments by enabling data availability for both legacy enterprise and cloud-native mission critical applications. By rev...
SYS-CON Events announced today that NetApp has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. NetApp is the data authority for hybrid cloud. NetApp provides a full range of hybrid cloud data services that simplify management of applications and data across cloud and on-premises environments to accelerate digital transformation. Together with their partners, NetApp emp...
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we'v...
SYS-CON Events announced today that TidalScale, a leading provider of systems and services, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale has been involved in shaping the computing landscape. They've designed, developed and deployed some of the most important and successful systems and services in the history of the computing industry - internet, Ethernet, operating s...
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant tha...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
Infoblox delivers Actionable Network Intelligence to enterprise, government, and service provider customers around the world. They are the industry leader in DNS, DHCP, and IP address management, the category known as DDI. We empower thousands of organizations to control and secure their networks from the core-enabling them to increase efficiency and visibility, improve customer service, and meet compliance requirements.
SYS-CON Events announced today that IBM has been named “Diamond Sponsor” of SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California.
Amazon is pursuing new markets and disrupting industries at an incredible pace. Almost every industry seems to be in its crosshairs. Companies and industries that once thought they were safe are now worried about being “Amazoned.”. The new watch word should be “Be afraid. Be very afraid.” In his session 21st Cloud Expo, Chris Kocher, a co-founder of Grey Heron, will address questions such as: What new areas is Amazon disrupting? How are they doing this? Where are they likely to go? What are th...
In a recent survey, Sumo Logic surveyed 1,500 customers who employ cloud services such as Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP). According to the survey, a quarter of the respondents have already deployed Docker containers and nearly as many (23 percent) are employing the AWS Lambda serverless computing framework. It’s clear: serverless is here to stay. The adoption does come with some needed changes, within both application development and operations. Tha...
SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Avere delivers a more modern architectural approach to storage that doesn't require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbui...
SYS-CON Events announced today that N3N will exhibit at SYS-CON's @ThingsExpo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. N3N’s solutions increase the effectiveness of operations and control centers, increase the value of IoT investments, and facilitate real-time operational decision making. N3N enables operations teams with a four dimensional digital “big board” that consolidates real-time live video feeds alongside IoT sensor data a...
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant th...