Migrating snippets from Kotlin learning guide

kotlin/build.gradle.kts

@@ -54,6 +54,7 @@ android {
     }
 }
 dependencies {
+    implementation("libs.androidx.compose.foundation:foundation")
     implementation(libs.androidx.lifecycle.viewmodel.ktx)
     implementation(libs.kotlinx.coroutines.android)
     testImplementation(libs.kotlinx.coroutines.test)

kotlin/src/main/kotlin/com/example/android/learn-kotlin/build.gradle.kts

@@ -0,0 +1,76 @@
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlin.compose)
+}
+
+android {
+    namespace = "com.example.kotlin_samples"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "com.example.kotlin_samples"
+        minSdk = 24
+        targetSdk = 36
+        versionCode = 1
+        versionName = "1.0"
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+    kotlinOptions {
+        jvmTarget = "11"
+    }
+    buildFeatures {
+        compose = true
+    }
+}
+
+dependencies {
+
+    // Core Android KTX for quality-of-life Kotlin extensions
+    implementation("androidx.core:core-ktx:1.13.1")
+
+    // Activity library with Compose integration for `setContent` and `enableEdgeToEdge`
+    implementation("androidx.activity:activity-compose:1.9.0")
+
+    // Jetpack Compose Bill of Materials (BOM)
+    // The BOM ensures that all of your Compose libraries use the same, compatible version.
+    val composeBom = platform("androidx.compose:compose-bom:2024.05.00")
+    implementation(composeBom)
+    androidTestImplementation(composeBom)
+
+    // Compose UI for core components like Modifier and layout primitives
+    implementation("androidx.compose.ui:ui")
+
+    // Compose Material 3 for Material Design components like Scaffold and Text
+    implementation("androidx.compose.material3:material3")
+
+    // Compose Foundation for building blocks like scrolling
+    implementation("androidx.compose.foundation:foundation")
+
+    // Tooling for displaying @Preview composables in Android Studio
+    implementation("androidx.compose.ui:ui-tooling-preview")
+    debugImplementation("androidx.compose.ui:ui-tooling")
+
+    // Other standard dependencies for testing and lifecycle management
+    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.8.1")
+    testImplementation("junit:junit:4.13.2")
+    androidTestImplementation("androidx.test.ext:junit:1.1.5")
+    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
+    androidTestImplementation("androidx.compose.ui:ui-test-junit4")
+    debugImplementation("androidx.compose.ui:ui-test-manifest")
+}

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

@@ -0,0 +1,220 @@
+/*
+ * 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
+
+import androidx.compose.ui.text.toUpperCase
+
+// 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 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 kotlin_defining_a_function]
+
+// [START 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 kotlin_function_with_parameter]
+
+// [START 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 kotlin_function_with_explicit_return]
+
+// [START 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 kotlin_function_as_single_expression]
+
+// [START kotlin_higher_order_function_definition]
+// From Snippet 14
+fun stringMapper(str: String, mapper: (String) -> Int): Int {
+    // Invoke function
+    return mapper(str)
+}
+// [END 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 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 kotlin_control_flow_if_else_if]
+}
+
+fun runSnippet2() {
+    // [START kotlin_control_flow_if_else]
+    if (count == 42) {
+        println("I have the answer.")
+    } else {
+        println("The answer eludes me.")
+    }
+    // [END kotlin_control_flow_if_else]
+}
+
+fun runSnippet3() {
+    // [START 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 kotlin_control_flow_if_as_expression]
+}
+
+fun runSnippet4() {
+    // [START 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 kotlin_control_flow_when_as_expression]
+}
+
+fun runSnippet5() {
+    // [START kotlin_null_safety_smart_cast]
+    val languageName: String? = null
+    if (languageName != null) {
+        // No need to write languageName?.toUpperCase()
+        println(languageName.toUpperCase())
+    }
+    // [END kotlin_null_safety_smart_cast]
+}
+
+fun runSnippet7() {
+    // [START kotlin_calling_a_function]
+    val answerString = generateAnswerString()
+    // [END kotlin_calling_a_function]
+}
+
+fun runSnippet9() {
+    // [START kotlin_calling_a_function_with_argument]
+    val answerString = generateAnswerString(42)
+    // [END kotlin_calling_a_function_with_argument]
+}
+
+fun runSnippet12() {
+    // [START kotlin_lambda_declaration]
+    val stringLengthFunc: (String) -> Int = { input ->
+        input.length
+    }
+    // [END kotlin_lambda_declaration]
+}
+
+fun runSnippet13() {
+    // [START kotlin_lambda_invocation]
+    val stringLengthFunc: (String) -> Int = { input ->
+        input.length
+    }
+
+    val stringLength: Int = stringLengthFunc("Android")
+    // [END kotlin_lambda_invocation]
+    // The original snippet did not print the result, so we don't either.
+}
+
+fun runSnippet15() {
+    // [START kotlin_higher_order_function_call_default]
+    stringMapper("Android", { input ->
+        input.length
+    })
+    // [END kotlin_higher_order_function_call_default]
+}
+
+fun runSnippet16() {
+    // [START kotlin_higher_order_function_call_trailing_lambda]
+    stringMapper("Android") { input ->
+        input.length
+    }
+    // [END kotlin_higher_order_function_call_trailing_lambda]
+}

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

@@ -0,0 +1,72 @@
+/*
+ * 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.kotlin_samples
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.verticalScroll
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.tooling.preview.Preview
+import androidx.compose.ui.unit.dp
+import com.example.kotlin_samples.ui.theme.KotlinsamplesTheme
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        setContent {
+            KotlinsamplesTheme {
+                // We replace the default Scaffold content with our new composable
+                SampleScreen()
+            }
+        }
+    }
+}
+
+@Composable
+fun SampleScreen(modifier: Modifier = Modifier) {
+    Scaffold(modifier = modifier.fillMaxSize()) { innerPadding ->
+        // Get the output from our LanguageSamples.kt file
+        val output = getLanguageSamplesOutput()
+
+        // Use a scrolling Text element to display the results
+        Text(
+            text = output,
+            modifier = Modifier
+                .padding(innerPadding)
+                .padding(16.dp) // Add some content padding
+                .fillMaxSize()
+                .verticalScroll(rememberScrollState()) // Make content scrollable
+        )
+    }
+}
+
+@Preview(showBackground = true)
+@Composable
+fun SampleScreenPreview() {
+    KotlinsamplesTheme {
+        SampleScreen()
+    }
+}