BAEL-892: Example of Sealed Classes (#2373)

kotlin/src/main/kotlin/com/baeldung/kotlin/Sealed.kt

@@ -0,0 +1,19 @@
+package com.baeldung.kotlin
+
+sealed class Result<out S, out F> {
+    abstract fun <R> map(func: (S) -> R) : Result<R, F>
+    abstract fun <R> mapFailure(func: (F) -> R) : Result<S, R>
+    abstract fun get() : S?
+}
+
+data class Success<out S, out F>(val success: S) : Result<S, F>() {
+    override fun <R> map(func: (S) -> R) : Result<R, F> = Success(func(success))
+    override fun <R> mapFailure(func: (F) -> R): Result<S, R> = Success(success)
+    override fun get(): S? = success
+}
+
+data class Failure<out S, out F>(val failure: F) : Result<S, F>() {
+    override fun <R> map(func: (S) -> R) : Result<R, F> = Failure(failure)
+    override fun <R> mapFailure(func: (F) -> R): Result<S, R> = Failure(func(failure))
+    override fun get(): S? = null
+}

kotlin/src/test/kotlin/com/baeldung/kotlin/SealedTest.kt

@@ -0,0 +1,84 @@
+package com.baeldung.kotlin
+
+import org.junit.Assert
+import org.junit.Test
+
+class SealedTest {
+    fun divide(a: Int, b: Int) : Result<Float, String> = when (b) {
+        0 -> Failure("Division by zero")
+        else -> Success(a.toFloat() / b)
+    }
+
+    @Test
+    fun testSuccess() {
+        val result = divide(10, 5)
+        Assert.assertEquals(Success<Float, String>(2.0f), result)
+    }
+
+    @Test
+    fun testError() {
+        val result = divide(10, 0)
+        Assert.assertEquals(Failure<Float, String>("Division by zero"), result)
+    }
+
+    @Test
+    fun testMatchOnSuccess() {
+        val result = divide(10, 5)
+        when (result) {
+            is Success -> {
+                // Expected
+            }
+            is Failure -> Assert.fail("Expected Success")
+        }
+    }
+
+    @Test
+    fun testMatchOnError() {
+        val result = divide(10, 0)
+        when (result) {
+            is Failure -> {
+                // Expected
+            }
+        }
+    }
+
+    @Test
+    fun testGetSuccess() {
+        val result = divide(10, 5)
+        Assert.assertEquals(2.0f, result.get())
+    }
+
+    @Test
+    fun testGetError() {
+        val result = divide(10, 0)
+        Assert.assertNull(result.get())
+    }
+
+    @Test
+    fun testMapOnSuccess() {
+        val result = divide(10, 5)
+                .map { "Result: $it" }
+        Assert.assertEquals(Success<String, String>("Result: 2.0"), result)
+    }
+
+    @Test
+    fun testMapOnError() {
+        val result = divide(10, 0)
+                .map { "Result: $it" }
+        Assert.assertEquals(Failure<Float, String>("Division by zero"), result)
+    }
+
+    @Test
+    fun testMapFailureOnSuccess() {
+        val result = divide(10, 5)
+                .mapFailure { "Failure: $it" }
+        Assert.assertEquals(Success<Float, String>(2.0f), result)
+    }
+
+    @Test
+    fun testMapFailureOnError() {
+        val result = divide(10, 0)
+                .mapFailure { "Failure: $it" }
+        Assert.assertEquals(Failure<Float, String>("Failure: Division by zero"), result)
+    }
+}