ValenciaJUG - Groovy for Java developers

class: center, middle

<h1>Groovy for Java developers</h1>
<p>By jjballano</p>
---
<h2>About me</h2>
<div class="about-me">
  <div>
    <img class="full-size" src="imgs/profile.jpg">
  </div>
  <div>
    <ul>
      <li>Software developer since more than 10 years ago.</li>
      <li>Started coding in Java.</li>
      <li>Have worked in several Groovy projects for the last 6 years.</li>
      <li>Currently working as freelance.</li>
    </ul>
  </div>
</div>
<div class="contact-info">
  <h3>Contact info</h3>
  <div><img class="icon" src="imgs/email.png" alt="Email icon"> <span>jjballano@gmail.com</span></div>
  <div><img class="icon" src="imgs/twitter.png" alt="Twitter icon"><span>@jjballano</span></div>
</div>
<div>
  <h3>Where to find this presentation</h3>
  <div><a href="https://valenciajug.jjballano.com">https://valenciajug.jjballano.com</a></div>
  <div>Github: <a href="https://github.com/jjballano/valenciajug_groovy">https://github.com/jjballano/valenciajug_groovy</a></div>
</div>

---
<h2>What's Groovy?</h2>
--
<img src="imgs/groovy-def.png" class="full-size"></img>
<ul>
  <li>This task will be focused in Groovy 2.4.x syntaxis</li>
  <li>At the moment of preparing this slides, 2.5 is in beta-2, 2.6 in alpha-2 and 3.0 in alpha-1</li>
</ul>
<p><p>
<footer><a href="http://groovy-lang.org/">Screenshot from groovy-lang.org</a><footer>

---
<h2>Optionally typed and dynamic language?</h2>
--
<ul>
  <li>Sure, you can set a type or use 'def'</li>
</ul>

```java
Integer typedNumber = 3
typedNumber = "new value" //GroovyCastException

def dynamicValue = 10
dynamicValue = "test"
assert dynamicValue == "test"
```

--
<ul>
  <li>But I try to use types as much as I can</li>
</ul>

--
<ul>
  <li>You can also use @CompileStatic annotation for checking errors and performance
</ul>

```Java
@groovy.transform.CompileStatic
Integer count(){
    return "just checking" //Compilation error
}

```

---
<h2>Wait a minute...</h2>
--
<ul>
  <li>Where are the semi-colons?</li>
</ul>
--
<ul>
  <li>Yeah! Not required</li>
</ul>
--
<ul>
  <li>Have you compared two strings with == operator?</li>
</ul>
--
<ul>
  <li>Yeah! why not? Who wants to know if two strings are the same object?</li>
</ul>
--
<ul>
  <li>Let me show you more good things about Groovy syntaxis</li>
</ul>

---
<h2>String and GString</h2>
--
<ul>
  <li>
    GString are interpolated strings
  </li>
</ul>

```Java
String name = "ValenciaJUG"

println "Hi ${name}" //Hi ValenciaJUG

println name.class //java.lang.String

println "Hi ${name}".class //org.codehaus.groovy.runtime.GStringImpl
```

--
<ul>
  <li>You can also compare strings and gstrings with == operator<li>
</ul>

```Java
String name = "ValenciaJUG"

"Hi ${name}" == "Hi ValenciaJUG"

"Hi" == "Hi"

"Hi ${name}" == "Hi ${name}"

"Hi ${name}" === "Hi Valencia" //False! And only for Groovy 2.6 and above
```

---
<h2>Collections</h2>

```java
List<Integer> values = [1,2,3]
```
```java
Set<Integer> values = [1,2,3,4,2,4,2]
assert values == [1,2,3,4] as Set
```

--
<h2>Maps</h2>

```java
String me = "Jesús"
Map<String, Integer> ages = ["Lucía": 23, Carlos: 27, (me): 25]

assert ages["Jesús"] == 25
assert ages.Carlos == 27
String name = "Lucía"
assert ages."${name}" == 23
```

---
<h2>Loops</h2>
--
<h3>each</h3>

```java
  List<Integer> values = [3, 4, 10]
```
```java
  values.each{ value ->
    println value * 2
  }  // will print 6, 8 and 20
```
--
```java
values.each{
  println it * 2
}  // "it" by default
```
--
```java
  (1..3).each {
    println it
  } // will print 1, 2 and 3 as (1..3) is a range
```
--
<h3>times</h3>

```java
  3.times{
    println it
  }  // it will print 0, 1 and 2
```

---
<h2>Loops</h2>

<h3>collect</h3>
<ul>
  <li>Returns a list with the result of last sentence of each iteration</li>
</ul>

```java
  List<Integer> values = [3, 4, 10]
  assert values.collect{ it * 2 } == [6, 8, 20]
```

<h3>collectEntries</h3>
<ul>
  <li>Returns a map with the result of last sentence of each iteration</li>
</ul>

```java
  List<Integer> values = [1,2,3]
  Map<String, Integer> transformed = values.collectEntries {
    String key = "value ${it}"
    [(key): it]
  }
  assert transformed == ["value 1":1, "value 2":2, "value 3":3]
```
<ul>
  <li>Result of last sentence within the block will be added to the list</li>
</ul>

---
<h2>Loops</h2>
<ul>
  <li>More loops:</li>
</ul>
--

```java
1.upto(10) { println it}
```
--
```java
10.downto(1) { println it}
```
--
```java
["a","b"].eachWithIndex { val, idx -> println "Value ${val} at position ${idx}"}
```
--
```java
Integer sum = [4,8].inject(0) { result, i -> result + i }
```
---
<h2>More methods for collections</h2>
--
<ul>
  <li>find, findAll</li>
</ul>

```java
  List<Integer> values = [1,2,3,4]

assert values.find{ it % 2 == 0 } == 2
  assert values.findAll{ it % 2 == 0 } == [2, 4]
```
--
<ul>
  <li>count, countBy</li>
</ul>

```java
  List<Integer> values = [1,2,3]

assert values.count{ it % 2 == 0 } == 1
  assert values.countBy{ it % 2 == 0 } == [(false): 2, (true):1]
```
--
<ul>
  <li>sort</li>
</ul>

```java
  List<Integer> values = [2,7,3,9]
  assert values.sort(false) == [2,3,7,9] //mutate by default true
  assert values == [2,7,3,9]

List<Map> mapValues = [[a:1, b:2], [a:4, b:4], [a:-1, b:9]]
  mapValues.sort{ it.a } == [[a:-1, b:9], [a:1, b:2], [a:4, b:4]]
```
---
<h2>Class DefaultGroovyMethods</h2>
<ul>
  <li>It's a Groovy class that defines many methods which appear on normal JDK classes inside the Groovy environment</li>
</ul>
--
<ul>
  <li>find, collect, each, with, etc. are defined in DefaultGroovyMethods</li>
</ul>
--
<ul>
  <li>Besides those, another one is asBoolean, very useful for if conditional</li>
</ul>

```Java
if (num){
  println "num not null or 0"
} else {
  println "num is null or 0"
}

```

???
This class defines methods that objects will contain out of the box.
---
<h2>Date</h2>
<ul>
  <li>Easy way of working with dates and TimeCategory</li>
</ul>

```Java
Date today = new Date()
today - 1 //yesterday
today.clearTime() //sets time to 00:00:00
today.format('dd-MM-yyyy') //30-01-2018
Date valenciaJUGDate = Date.parse('dd-MM-yyyy', '30-01-2018')
today.downto(new Date() - 10) { println it }

use(groovy.time.TimeCategory){
  today - 10.minutes
  today + 3.months
}
```

---
<h2>Classes and methods</h2>

```java
class MyClass {

String attribute = "value"

List getAll(){ //the code }

void set(String name){ //the code }

def getName(){ return "Jesús" }

private String getValue(){ "Value in private method" }
}

MyClass myObject = new MyClass()
assert myObject.attribute == "value"
assert myObject.getAttribute() == "value"
myObject.attribute = "different value"
assert myObject.attribute == "different value"
myObject.setAttribute("with setter")
assert myObject.attribute == "with setter"

```
<ul>
  <li>Methods can be typed, dynamic or void</li>
  <li>By default, all attributes are public and have their getter and setter </li>
  <li>Methods will return last sentence unless it's void, so 'return' is optional</li>
</ul>

---
<h2>Classes and methods</h2>

```java
class MyClass {

String getValue(){
    "the value"
  }
}

```
<ul>
  <li>Getters and setters can be used as properties</li>
</ul>

```java
MyClass myObject = new MyClass()
assert myObject.value == "the value"
```

---
<h2>Classes and methods</h2>

```java
class MyClass {

private String privateAttribute = "private"

private String getValue(){
    "Value in private method"
  }
}

MyClass myObject = new MyClass()
assert myObject.privateAttribute == "private"
new myObject.getPrivateAttribute() //groovy.lang.MissingMethodException

assert myObject.value == "Value in private method"

```
<ul>
  <li>Private attributes don't have getter and setter</li>
  <li>Private attributes and methods are not really private... Quite weird, I know</li>
</ul>

---
<h2>Classes and methods</h2>

```java
class MyClass {

String getValue(){
    "Value in method"
  }
}

MyClass myObject = new MyClass()
String attribute = "value"
assert myObject."${attribute}" == "Value in method"

```

<ul>
  <li>Methods and attributes can be accessed with string values</li>
</ul>

---
<h2>Classes and methods</h2>

```java
class MyClass {

String "method name"(){
    "Value in method"
  }
}

MyClass myObject = new MyClass()
assert myObject."method name"() == "Value in method"

```

<ul>
  <li>Methods can be named with strings. Very useful for testing methods</li>
</ul>

---
<h2>Classes and methods</h2>

```java
class MyClass {
  String name
}

MyClass myObject = new MyClass([name: "Jesús"])
//brackets not needed -> new MyClass(name: "Jesús")
assert myObject.name == "Jesús"
```

<ul>
  <li>Classes always have a constructor that receives a Map and sets all properties</li>
</ul>

---
<h2>Classes and methods</h2>
<h3>with</h3>

```java
class MyClass {
  String name = "Jesús"
}

MyClass myObject = new MyClass()
myObject.with{
  assert name == "Jesús"
}
```
---
<h2>Closures</h2>
--
<ul>
  <li>As you've already seen in loops before, Groovy has closures</li>
</ul>
--
<ul>
  <li>Their syntaxis is </li>
</ul>

```java
{ [closureParameters -> ] statements }
```

--
<ul>
  <li>Always return the result of last sentence, as methods do</li>
</ul>

--
<ul>
  <li>They can be assigned to a variable</li>
</ul>

```java
Closure sayHi = { "Hi, ${it}" }
assert sayHi('ValenciaJUG') == "Hi, ValenciaJUG"
```

--
<ul>
  <li>And used in methods as parameters</li>
</ul>

```java
String tellMeSomething(Closure closure){
    closure.call("ValenciaJUG")
  }

assert tellMeSomething{ name -> "Hi, ${name}" } == "Hi, ValenciaJUG"
//parentheses not needed when you call a method
```

---
<h2>Traits</h2>
<ul>
  <li>Similar to mixins in other languages</li>
</ul>

```java
trait MyTrait {
    String name = "Jesús"
    String sayHello() { "Hello from the trait" }
}
class MyClass implements MyTrait{

}

MyClass myObject = new MyClass()
assert myObject.sayHello() == "Hello from the trait"
assert myObject.name == "Jesús"
```
<ul>
  <li>Methods and attributes can be overridden within the class</li>
</ul>
---
<h2>Null safe operator ( ? )</h2>
<ul>
  <li>You don't need to constantly check if an object is null</li>
  <li>Avoid NullPointerException</li>
</ul>

```java
String name = null
assert name?.size() == null
```

---
<h2>Elvis operator ( ?: ) </h2>

<ul>
  <li>Less verbose ternary operator</li>
  <li>Return the conditional expression if it evaluates to true</li>
</ul>

```java
Integer value = 0
println value ?: 10 //print 10

value = 20
println value ?: 10 //print 20
```
--

<ul>
  <li>Why Elvis?</li>
</ul>

---
<h2>Spread operator ( * )</h2>
<ul>
  <li>Gets all values for a property in a list of objects</li>
</ul>

```java

class User {
    String name
}

List<User> users = [new User(name: "Jesús"), new User(name: "Miguel Ángel")]
assert users*.name == ["Jesús", "Miguel Ángel"]
```
--
<ul>
  <li>* is optional, but I rather use it to make the code clearer</li>
</ul>

```java
assert users.name == ["Jesús", "Miguel Ángel"]
```
---
<h2>Try it yourself</h2>
<ul>
  <li>Groovy installation comes with a tool called Groovy Console where you can test any groovy code</li>
</ul>
<img src="imgs/groovyconsole.png" class="full-size">

---
<h2>Ecosystem</h2>
<ul>
  <li>Groovy has a good ecosystem of products around it, here some of the most important ones you can use with groovy</li>
</ul>
--
<ul>
  <li><b>SDKMAN!</b>: Tool for managing parallel versions of multiple Software Development Kits</li>
</ul>
--
<ul>
  <li><b>Grails</b>: Web application framework for the JVM built on top of Spring Boot</li>
</ul>
--
<ul>
  <li><b>Spock</b>: Testing and specification framework</li>
</ul>
--
<ul>
  <li><b>Geb</b>: Browser functional testing framework</li>
</ul>
--
<ul>
  <li>Other software used in Java enviroment such as <b>Gradle</b>, <b>Griffon</b>, <b>Ratpack</b>, etc, are also used in Groovy projects</li>
</ul>

---
<h2>Questions?</h2>
<div class="questions">
  <img src="imgs/questionmark.png">
</div>

---
<div>
  <img src="imgs/thanks.jpg" class="full-size">
</div>
<div class="contact-info">
  <div><img class="icon" src="imgs/email.png" alt="Email icon"> <span>jjballano@gmail.com</span></div>
  <div><img class="icon" src="imgs/twitter.png" alt="Twitter icon"><span>@jjballano</span></div>
</div>
<div>
  <div><a href="https://valenciajug.jjballano.com">https://valenciajug.jjballano.com</a></div>
</div>