[Kotlin] added data class, enum, sealed class

working on generics

Author: Catherine22

KotlinFromScratch/.idea/workspace.xml

@@ -0,0 +1,19 @@
+class DataClass {
+    fun test() {
+        println("Properties declared in the primary constructor")
+        val scout = User("Scout", 15, "F")
+        val (name, age) = scout
+        println("$name, $age years of age")
+
+        val jack = User(age = 12, name = "Jack")
+        val olderJack = jack.copy(age = 20)
+        println("$jack.name, $jack.age years of age")
+        println("$olderJack.name, $olderJack.age years of age")
+
+
+        println("")
+        println("Properties declared in the class body")
+        val employee = Employee("Michael")
+        employee.age = 18
+    }
+}

KotlinFromScratch/src/DataClass.kt

@@ -0,0 +1,4 @@
+data class Employee(val name: String) {
+    var age: Int = 0
+    var gender: String = "M"
+}

KotlinFromScratch/src/Employee.kt

@@ -0,0 +1,25 @@
+class Generics {
+    interface Source<out T> {
+        fun nextT(): T
+    }
+
+    private fun demo(source: Source<String>) {
+        // Declaration-site variance
+        val objects: Source<Any> = source
+        println(objects.nextT())
+    }
+
+    fun test() {
+        println("Declaration-site variance")
+        // Declaration-site variance -> In Java, we can't declare type String to type Object
+        demo(object : Source<String> {
+            override fun nextT(): String {
+                return "next"
+            }
+        })
+
+
+        println("")
+        println("Type projections")
+    }
+}

KotlinFromScratch/src/Generics.kt

@@ -14,6 +14,15 @@ fun main(args: Array<String>) {
 //    val propertiesAndFields = PropertiesAndFields()
 //    propertiesAndFields.test()
 
-    val baseClass = BaseClass()
-    baseClass.test()
+//    val baseClass = BaseClass()
+//    baseClass.test()
+
+//    val dataClass = DataClass()
+//    dataClass.test()
+
+//    val sealedClass = SealedClass()
+//    sealedClass.test()
+
+    val generics = Generics()
+    generics.test()
 }

KotlinFromScratch/src/Main.kt

@@ -0,0 +1,48 @@
+class SealedClass {
+    fun test() {
+
+        println("enum")
+        val state = EnumState.PLAYING
+        println(getStateDescription(state))
+
+        println("")
+        println("Replaced with sealed class")
+        val playerA = SealedState.Play("A")
+        println(getSealedStateDescription(playerA))
+        val defaultPlayer = SealedState.PLAYING_
+        println(getSealedStateDescription(defaultPlayer))
+    }
+
+    private fun getStateDescription(state: EnumState) = when (state) {
+        EnumState.PAUSE -> "Player is paused"
+        EnumState.IDLE -> "Player is idle"
+        EnumState.PLAYING -> "Player is playing"
+        EnumState.STOP -> "Player is stopped"
+    }
+
+    private fun getSealedStateDescription(state: SealedState) = when (state) {
+        SealedState.PAUSE_ -> "Player is paused"
+        SealedState.IDLE_ -> "Player is idle"
+        SealedState.PLAYING_ -> "Player is playing"
+        SealedState.STOP_ -> "Player is stopped"
+        is SealedState.Pause -> "Player ${state.name} is paused"
+        is SealedState.Play -> "Player ${state.name} is playing"
+        is SealedState.Idle -> "Player ${state.name} is idle"
+        is SealedState.Stop -> "Player ${state.name} is stopped"
+    }
+}
+
+enum class EnumState {
+    PAUSE, PLAYING, IDLE, STOP
+}
+
+sealed class SealedState {
+    data class Pause(val name: String) : SealedState()
+    data class Play(val name: String) : SealedState()
+    data class Idle(val name: String) : SealedState()
+    data class Stop(val name: String) : SealedState()
+    object PAUSE_ : SealedState()
+    object PLAYING_ : SealedState()
+    object IDLE_ : SealedState()
+    object STOP_ : SealedState()
+}

KotlinFromScratch/src/SealedClass.kt

@@ -0,0 +1 @@
+data class User(val name: String, val age: Int, val gender: String = "M")

KotlinFromScratch/src/User.kt

@@ -232,6 +232,15 @@ The exam is only available in Java at this time (4/1/2019)
     - Companion objects (which is similar to ```static```)     
     - Call extension functions of the base class declared other class       
     - Call functions both declared in the base class and self class inside extension functions (check [BaseClassExtensions])      
+8. [Data Class], [User], [Employee]     
+    - Properties declared in the primary constructor or class body      
+    - Copying       
+9. [enum and sealed class]             
+    - enum vs sealed class      
+10. [Generics]      
+    - Declaration-site variance     
+    - Type projections      
+
 
 
 
@@ -260,6 +269,10 @@ The exam is only available in Java at this time (4/1/2019)
 [Visibility Modifiers]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/package1/VisibilityModifiers.kt>
 [BaseClass]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/BaseClass.kt>
 [BaseClassExtensions]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/BaseClassExtensions.kt>
+[Data Class]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/DataClass.kt>
+[User]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/User.kt>
+[Employee]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/Employee.kt>
+[enum and sealed class]:<https://github.com/Catherine22/AAD-Preparation/blob/master/KotlinFromScratch/src/SealedClass.kt>
 
 [CallLogProvider]:<https://android.googlesource.com/platform/packages/providers/ContactsProvider/+/refs/tags/android-9.0.0_r34/src/com/android/providers/contacts/CallLogProvider.java>