Migrating snippets from Kotlin learning guide

kotlin/src/main/kotlin/com/example/android/learn-kotlin/java/com/example/kotlin_samples/KotlinSamples.kt

@@ -0,0 +1,218 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.kotlin.snippets
+
+// A top-level constant used by the snippets below.
+private const val count = 42
+
+/*
+ * The following are function definitions from the provided snippets.
+ * They are defined at the top level so they can be called by other snippets.
+ * Some have been given unique names to prevent compilation errors, but their
+ * bodies are unchanged.
+ */
+
+// [START android_kotlin_defining_a_function]
+// From Snippet 6
+fun generateAnswerString(): String {
+    val answerString = if (count == 42) {
+        "I have the answer."
+    } else {
+        "The answer eludes me"
+    }
+
+    return answerString
+}
+// [END android_kotlin_defining_a_function]
+
+// [START android_kotlin_function_with_parameter]
+// From Snippet 8
+// Note: This function has the same signature as the one from Snippet 10 and 11.
+// It is kept here as the primary example.
+fun generateAnswerString(countThreshold: Int): String {
+    val answerString = if (count > countThreshold) {
+        "I have the answer."
+    } else {
+        "The answer eludes me."
+    }
+
+    return answerString
+}
+// [END android_kotlin_function_with_parameter]
+
+// [START android_kotlin_function_with_explicit_return]
+// From Snippet 10
+fun generateAnswerStringWithExplicitReturn(countThreshold: Int): String {
+    return if (count > countThreshold) {
+        "I have the answer."
+    } else {
+        "The answer eludes me."
+    }
+}
+// [END android_kotlin_function_with_explicit_return]
+
+// [START android_kotlin_function_as_single_expression]
+// From Snippet 11
+fun generateAnswerStringAsExpression(countThreshold: Int): String = if (count > countThreshold) {
+    "I have the answer"
+} else {
+    "The answer eludes me"
+}
+// [END android_kotlin_function_as_single_expression]
+
+// [START android_kotlin_higher_order_function_definition]
+// From Snippet 14
+fun stringMapper(str: String, mapper: (String) -> Int): Int {
+    // Invoke function
+    return mapper(str)
+}
+// [END android_kotlin_higher_order_function_definition]
+
+
+/**
+ * The main entry point for this file. Running this function will execute
+ * each of the original snippets in order.
+ */
+fun main() {
+    println("--- Snippet 1 ---")
+    runSnippet1()
+    println("\n--- Snippet 2 ---")
+    runSnippet2()
+    println("\n--- Snippet 3 ---")
+    runSnippet3()
+    println("\n--- Snippet 4 ---")
+    runSnippet4()
+    println("\n--- Snippet 5 ---")
+    runSnippet5()
+    println("\n--- Snippet 7 (no output) ---")
+    runSnippet7()
+    println("\n--- Snippet 9 (no output) ---")
+    runSnippet9()
+    println("\n--- Snippet 12 (no output) ---")
+    runSnippet12()
+    println("\n--- Snippet 13 ---")
+    runSnippet13()
+    println("\n--- Snippet 15 (no output) ---")
+    runSnippet15()
+    println("\n--- Snippet 16 (no output) ---")
+    runSnippet16()
+}
+
+fun runSnippet1() {
+    // [START android_kotlin_control_flow_if_else_if]
+    if (count == 42) {
+        println("I have the answer.")
+    } else if (count > 35) {
+        println("The answer is close.")
+    } else {
+        println("The answer eludes me.")
+    }
+    // [END android_kotlin_control_flow_if_else_if]
+}
+
+fun runSnippet2() {
+    // [START android_kotlin_control_flow_if_else]
+    if (count == 42) {
+        println("I have the answer.")
+    } else {
+        println("The answer eludes me.")
+    }
+    // [END android_kotlin_control_flow_if_else]
+}
+
+fun runSnippet3() {
+    // [START android_kotlin_control_flow_if_as_expression]
+    val answerString: String = if (count == 42) {
+        "I have the answer."
+    } else if (count > 35) {
+        "The answer is close."
+    } else {
+        "The answer eludes me."
+    }
+
+    println(answerString)
+    // [END android_kotlin_control_flow_if_as_expression]
+}
+
+fun runSnippet4() {
+    // [START android_kotlin_control_flow_when_as_expression]
+    val answerString = when {
+        count == 42 -> "I have the answer."
+        count > 35 -> "The answer is close."
+        else -> "The answer eludes me."
+    }
+
+    println(answerString)
+    // [END android_kotlin_control_flow_when_as_expression]
+}
+
+fun runSnippet5() {
+    // [START android_kotlin_null_safety_smart_cast]
+    val languageName: String? = null
+    if (languageName != null) {
+        println(languageName.uppercase())
+    }
+    // [END android_kotlin_null_safety_smart_cast]
+}
+
+fun runSnippet7() {
+    // [START android_kotlin_calling_a_function]
+    val answerString = generateAnswerString()
+    // [END android_kotlin_calling_a_function]
+}
+
+fun runSnippet9() {
+    // [START android_kotlin_calling_a_function_with_argument]
+    val answerString = generateAnswerString(42)
+    // [END android_kotlin_calling_a_function_with_argument]
+}
+
+fun runSnippet12() {
+    // [START android_kotlin_lambda_declaration]
+    val stringLengthFunc: (String) -> Int = { input ->
+        input.length
+    }
+    // [END android_kotlin_lambda_declaration]
+}
+
+fun runSnippet13() {
+    // [START android_kotlin_lambda_invocation]
+    val stringLengthFunc: (String) -> Int = { input ->
+        input.length
+    }
+
+    val stringLength: Int = stringLengthFunc("Android")
+    // [END android_kotlin_lambda_invocation]
+    // The original snippet did not print the result, so we don't either.
+}
+
+fun runSnippet15() {
+    // [START android_kotlin_higher_order_function_call_default]
+    stringMapper("Android", { input ->
+        input.length
+    })
+    // [END android_kotlin_higher_order_function_call_default]
+}
+
+fun runSnippet16() {
+    // [START android_kotlin_higher_order_function_call_trailing_lambda]
+    stringMapper("Android") { input ->
+        input.length
+    }
+    // [END android_kotlin_higher_order_function_call_trailing_lambda]
+}
+