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@charlesmuchene
Working with Java & Kotlin
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Agenda
• What is Kotlin?
• Kotlin - Java interoperability
• Kotlin on Spring
• Kotlin on Android
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Compilation
Java Source Java Compiler Java Bytecode
Student.java Student.class
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Compilation + Execution
Sources
Bytecode
JVM
Application
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Execution
Bytecode JVM Application
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JVM
Kotlin
Java
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Why Kotlin?
Concise Safe Interoperable Tooling
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Kotlin
Android
JVM Web Native
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Kotlin
Android
JVM
Web Native
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Code demo
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Kotlin + Spring
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Person RESTful API
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Application File
@SpringBootApplication
class Application
fun main(args: Array) {
runApplication(*args)
}
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Person Controller
@RestController
class PersonController(private val personRepository: PersonRepository) {
@GetMapping("/person")
fun readAll() = personRepository.findAll()
@GetMapping("/person/{id}")
fun readOne(@PathVariable id: Long) = personRepository.findById(id)
}
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Person Class
@Entity
data class Person(@Id val id: Long, val firstName: String, ...
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Running Spring Boot App
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App demo
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Kotlin + Android
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Countries App
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Countries App Flow
Launch Fetch online Display
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No content
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Main Activity
class MainActivity : AppCompatActivity() {
private lateinit var viewModel: CountryViewModel
private var countryAdapter = CountryAdapter()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
...
}
...
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Country Details ViewModel
class CountryDetailsViewModel : ViewModel() {
fun getDetails(country: Country): String = with(country) {
"""
Native Name: $nativeName
Demonym: ${demonym.orDash}
Population: ${String.format("%,d", population)}
Language(s): ${languages.joinToString(transform = Language::toString)}
Currency: ${currencies.joinToString(transform = Currency::toString)}
Timezone(s): ${timezones.joinToString()}
""".trimIndent()
}
}
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Country Class
@Parcelize
data class Country(val name: String, val capital: String, ...
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App demo
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Kotlin Love - StackOverflow
https://insights.stackoverflow.com/survey/2018/#technology
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Kotlin Interest - StackOverflow
https://insights.stackoverflow.com/survey/2018/#technology
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Kotlin Interest - Hackerrank
https://research.hackerrank.com/developer-skills/2019
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Resources
• https://kotlinlang.org/
• https://insights.stackoverflow.com/survey/2018
• https://research.hackerrank.com/developer-skills/2019
• https://github.com/charlesmuchene/learn-kotlin-app
• https://github.com/charlesmuchene/learn-kotlin-jvm
• https://github.com/charlesmuchene/learn-kotlin-spring-boot
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charlesmuchene