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Mastering Groovy

Table of Contents

Chapter 1: Introduction

Test. Let us learn Groovy. It has different use cases and learning it is probably good for your career as well :) No it will definitely be beneficial. Groovy is a programming language with Java like syntax which came into existence in 2003. To know more you can go to https://groovy-lang.org/ the official site.

Optionally type: As compared to Java you are not required to declare the variable type.

def a = 123
def b = 123.5
def c = "I am a string"

Dynamic programming language: Data type is checked at run time.

In Java you have to declare the data type before you can use it.

int i;
i = 10;

Whereas in Groovy no need to declare the data type.

i = 10

Tip: Watch Introduction and what is Groovy. 1

Who this book is for?

So wondering if this book can help you or not?

  • If you are like me who has programming experience already but for some reason wants to learn Groovy then this book is for you.
  • You want to learn automation in Jira.

Tip: Apart from reading this book I also recommend you to take a look at the video Mastering Groovy playlist on YouTube (completely free of cost).

Getting started with Groovy

Installation

Go to www.groovy-lang.org and download or set it up on your system. It works on Windows, Linux and Mac. Since I am doing it on Mac so you can simply install Groovy using brew. I highly recommend you to read this page first to find out the distribution suitable for you.

  • Prerequisites

    Groovy requires Java. So install it first. Check the system requirements on the link shared above.

    java -version
    
  • Install Groovy on Mac
    brew install groovy
    
  • Install Groovy on Windows

    You can download the windows installer from the download page.

  • Install Groovy on Linux

    There several methods but one simple way is to use SDKMAN. Instructions can be found on this page.

  • Manual installation

    If you are little adventurous then you can also install it manually.

    • Download the zip and unpack it to a local directory.
    • Set GROOVY_HOME envrionment variable to that directory.
    • Add GROOVY_HOME/bin to your PATH variable. Basically this will ensure you can run groovysh from any directory on your operating system.
    • Set your JAVA_HOME envrionment varible to point to you JDK.

Initial checks

If you have managed to successfully install Groovy as mentioned above then now it is time to verify your installation and check groovy version on your terminal.

groovy --version

If groovy is installed then you should get something like this on your terminal.

Groovy Version: 3.0.7 JVM: 15.0.2 Vendor: Oracle Corporation OS: Linux

Check for groovy shell.

groovysh --version
@ green Groovy Shell @ 3.0.7

Groovy also comes with a compiler.

groovyc --version
Groovy compiler version 3.0.7      
Copyright 2003-2020 The Apache Software Foundation. http://groovy-lang.org/
             

Tip: Watch a video on how to install Groovy and different checks. 2

Tools you need for learning Groovy

There are different tools you can use to run groovy scripts.

  • Groovy web console

    Yes you can try Groovy without installing anything on your computer if you have Internet connection (and a computer as well I guess).

    Click here to get started.

  • Groovy Console

    From your terminal run Groovy Console.

    groovyConsole
    
  • IntelliJ IDE

    You can install IntelliJ, it has a free community edition that works perfectly and it is all you need to learn Groovy and develop. It works on Mac, Windows and Lunux.

    Using IntelliJ is very easy. Here are the steps to get started with IntelliJ.

    • Launch IntelliJ.
    • Create New Project.
    • Select Groovy.
    • Configure Project SDK and point it to your JDK installed on your computer. The location should be same as JAVA_HOME location.
    • Configure Groovy library and point it to the directory where you installed it. Check which groovy to know the location. On Mac the .sdkman folder is hidden, so to find it in the Finder use a shortcut Command+Shift+dot.
    • Click Next.
    • Enter Project name and Project location.
    • On the left side there is a src folder. Right click on it | New | Package and enter something like in.ravisagar.masteringgroovy. This will help in organising the code better.
    • Inside the package create a new Groovy Script helloWorld.groovy.
    package in.ravisagar.masteringgroovy
    println "Hello World"
    
    • Right click on helloWorld.groovy | Run 'helloWorld'
    Hello World
    

    Check the video. 3

Chapter 2: Groovy fundamentals

Write code for FizzBuzz game

The best way to learn a programming language is by getting your hands dirty. The more you write code solving different problems, the better you will become.

What FizzBuzz?

It is a popular game used to teach children (and adults) about division. Player take turn to count numbers from 1 to let us say 100, replacing any number divisible by 3 with Fizz, any number divisible by 5 with Buzz and any number divisible by both 3 and 5 with FizzBuzz.

The output will be like 1, 2, Fizz, 4, Buzz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, Fizzbuzz, 16, …

Simple right?

Let us write code for it.

package in.ravisagar.masteringgroovy

for (int i = 1;i<=100;i++) {

    if (i%3==0 && i%5 ==0) {println "FizzBuzz"}

    else if (i%3==0) {println "Fizz"}

    else if (i%5 ==0) {println "Buzz"}

    else {println i }

}

You can watch this video as well. 4

Comments

Single line comment

// Comment on a single line
println "My name is Ravi" //Yes that is my name

Multi line comment

/* Comment spanning more than
   one line */
println "We are learning about comments"

Groovydoc comment

Starts with /** and end with */. Main purpose is to generate documents that will explain your classes.

/**
 * A Class description
 */

Shebang line

This is for allowing groovy code to be run from the command line on UNIX based systems. Of course groovy should be installed and in your path.

Create a file called in.ravisagar.masteringgroovy.shebang.groovy with the following simple code.

#!/usr/bin/env groovy
println "This is testing the in.ravisagar.masteringgroovy.shebang comment"

Make the file executable.

chmod a+x in.ravisagar.masteringgroovy.shebang.groovy
./in.ravisagar.masteringgroovy.shebang.groovy

Variables and Data types

A container that can store a value used in the program. Those values can be updated as needed during the execution of the program. In the previous FizzBuzz program we used variable int i. We were kind enough to declare data type of i which brings us to the concept of data types.

Variable declarations

We can tell the compiler in advanced how to use the variable. It can be declared by their type like int i or String name or also by using def num or var k.

Data types

Let me start by asking you what is the difference between 123 and India? No prize for guessing. First one is a number but second one is a string. Now let me ask you one more question. Is 123 different from 123.5? Both are numbers but 123.5 has a fraction.

I hope you get the idea. When you are using variables in Groovy you have the option to also define them with their data type. This make it easier for the compiler to know their purpose. Although you Groovy doesn't require you to define variable or their data types.

Write code to write file to file system and also delete a file

Let us get our hands dirty again. If you are going to use Groovy then sooner or later you will be working with files. So today let us write a simple code to write a file

package in.ravisagar.masteringgroovy
import java.io.File

def currentDirectory = System.getProperty("user.dir")
def fileName = "testFile.txt"

File file = new File(currentDirectory+"/"+fileName)
file.write("This is great")
file.delete()

Methods in Groovy

Let us say you have to sum two numbers. Of course no rocket science here and you can write small piece of code to do it.

def a = 1
def b = 2
c = a + b

assert(3) == c

What if you want to calculate difference between two dates? Sure it is nothing too complicated and can be done with fews lines of code (or even less) but what if you have to calculate this date difference multiple times during your code execution?

That is where methods come into picture.

  • You define a method and give them a task to perform (like adding two number).
  • Their job is to perform that function whenever you want.
  • So if you have to calculate date difference between two date you simple ask this method or call it.
  • When you call that method just pass those two dates as parameters.

Let us understand this with a simple example.

package in.ravisagar.masteringgroovy
def a = 1
def b = 3
def c = a + b
assert(4) == c
println "a + b = " + c

def sumTwoNumbers(a,b) {

c = a + b
return c

}

println "a + b = " + sumTwoNumbers(a,b)

In the example above we are adding two numbers. We defined a simple method to perform this task for us.

Methods are really important not just in Groovy but in any programming language. It makes your life much easy and helps you achieve your goals with less lines of code.

Collections in Groovy

Probably one of the most important feature. Groovy has collection types - list, maps and ranges. From my personal experience I can tell you that will be using collections quite a lot.

List

  • Let us define a list and do some basic operations.
    def emptyList = []
    assert emptyList.size() == 0 //Check size of the list
    
    def listNumber = [1,2,3,4]
    assert listNumber.size() == 4
    assert listNumber == [1,2,3,4]
    assert listNumber.get(0) == 1 //Get the value at first position
    assert listNumber[1] == 2 //Get the value at second position
    assert listNumber instanceof java.util.List
    assert listNumber.contains(3) == true //contains() is a method to search within a list
    
    listNumber.add(5)
    assert listNumber == [1,2,3,4,5]
    listNumber.addAll([6,7]) //Add all the individual members
    assert listNumber == [1,2,3,4,5,6,7]
    
  • Iterating a list

    If you are learning Groovy then I can tell you that you will be doing lot of work with lists.

    package in.ravisagar.masteringgroovy
    
    def listCountries = ["UK","India","USA", "France"]
    assert listCountries == ["UK","India","USA", "France"]
    
    listCountries.each {
    println "Country: $it" //it is the current element
    }
    
    listCountries.eachWithIndex { i, it -> //it is the current element and i is the index
    println "$i: $it"
    
    }
    

Footnotes:

1

MasteringGroovy - Introduction and what is Groovy: Video

2

MasteringGroovy - Getting started, installing and initial checks: Video

3

MasteringGroovy - IntelliJ and Groovy Console: Video

4

MasteringGroovy - FizzBuzz code in Groovy | Popular children game & interview question: video