Lec20

src/main/java/com/lannstark/lec18/Fruit.kt

@@ -0,0 +1,15 @@
+package com.lannstark.lec18;
+
+data class Fruit(
+    val id: Long,
+    val name: String,
+    val factoryPrice: Long,
+    val currentPrice: Long?,
+) {
+    fun nullOrValue(): Long? {
+        return currentPrice
+    }
+
+    val isSamePrice: Boolean
+        get() = factoryPrice == currentPrice
+}

src/main/java/com/lannstark/lec18/Lec18Main.kt

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+package com.lannstark.lec18;
+
+import java.util.*
+
+fun main() {
+
+    val fruits = Arrays.asList(
+        Fruit(1, "사과", 1000, 1400),
+        Fruit(2, "사과", 1200, 1400),
+        Fruit(3, "사과", 1200, null),
+        Fruit(4, "사과", 1500, 1600),
+        Fruit(5, "바나나", 3000, 3400),
+        Fruit(6, "바나나", 3200, 3500),
+        Fruit(7, "바나나", 2500, 2800),
+        Fruit(8, "수박", 10000, 12000)
+    )
+
+    val fruitsInList: List<List<Fruit>> = listOf(
+        listOf(
+            Fruit(1L, "사과", 1_000, 1_500),
+            Fruit(2L, "사과", 1_200, 1_500),
+            Fruit(3L, "사과", 1_200, 1_500),
+            Fruit(4L, "사과", 1_500, 1_500),
+        ),
+        listOf(
+            Fruit(5L, "바나나", 3_000, 3_200),
+            Fruit(6L, "바나나", 3_200, 3_200),
+            Fruit(7L, "바나나", 2_500, 3_200),
+        ),
+        listOf(
+            Fruit(8L, "수박", 10_000, 10_000),
+        ),
+    )
+
+}
+
+private fun filterFruits(fruits: List<Fruit>, filter: (Fruit) -> Boolean): List<Fruit> {
+    val results = mutableListOf<Fruit>()
+    for (fruit in fruits) {
+        if (filter(fruit)) {
+            results.add(fruit)
+        }
+    }
+    return results
+}
+
+val List<Fruit>.samePriceFilter: List<Fruit>
+    get() = this.filter(Fruit::isSamePrice)

src/main/java/com/lannstark/lec19/Fruit.kt

@@ -0,0 +1,15 @@
+package com.lannstark.lec19
+
+data class Fruit(
+    val id: Long,
+    val name: String,
+    val factoryPrice: Long,
+    val currentPrice: Long?,
+) {
+    fun nullOrValue(): Long? {
+        return currentPrice
+    }
+
+    val isSamePrice: Boolean
+        get() = factoryPrice == currentPrice
+}

src/main/java/com/lannstark/lec19/Lec19Main.kt

@@ -0,0 +1,24 @@
+package com.lannstark.lec19
+
+fun main() {
+    val numbers = listOf(1, 2, 3)
+}
+
+fun filterFruits(fruits: List<Fruit>, filter: (Fruit) -> Boolean) {
+
+}
+
+data class Person(
+    val name: String,
+    val age: Int
+)
+
+const val number = 0
+
+fun getNumberOrNull(): Int? {
+    return if (number <= 0) {
+        null
+    } else {
+        number
+    }
+}

src/main/java/com/lannstark/lec19/a/Print.kt

@@ -0,0 +1,5 @@
+package com.lannstark.lec19.a
+
+fun printHelloWorld() {
+    println("Hello World A")
+}

src/main/java/com/lannstark/lec19/b/Print.kt

@@ -0,0 +1,5 @@
+package com.lannstark.lec19.b
+
+fun printHelloWorld() {
+    println("Hello World B")
+}

src/main/java/com/lannstark/lec20/Lec20Main.kt

@@ -0,0 +1,32 @@
+package com.lannstark.lec20
+
+fun main() {
+    val person = Person("홍길동", 100)
+
+    val value1 = person.let {
+        it.age
+    }
+
+    val value2 = person.run {
+        this.age
+    }
+
+    val value3 = person.also {
+        it.age
+    }
+
+    val value4 = person.apply {
+        this.age
+    }
+
+    mutableListOf("one", "two", "three")
+        .also { println("The list elements before adding new one: ${it}") }
+        .add("four")
+}
+
+fun printPerson(person: Person?) {
+    if (person != null) {
+        println(person.name)
+        println(person.age)
+    }
+}

src/main/java/com/lannstark/lec20/Person.kt

@@ -0,0 +1,8 @@
+package com.lannstark.lec20
+
+class Person constructor (
+    var name: String,
+    var age: Int,
+) {
+
+}