[KTLN-799] Getting All Field Names of a Class Using Kotlin Reflection (#873)

* added unit test

* code fixes

* code fixes

Author: albertache1998

kotlin-reflection/src/test/kotlin/com/baeldung/getFieldNamesWithReflection/GetAllFieldsUsingReflectionUnitTest.kt

@@ -0,0 +1,72 @@
+package com.baeldung.getFieldNamesWithReflection
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+import kotlin.reflect.KClass
+import kotlin.reflect.KProperty
+import kotlin.reflect.KProperty1
+import kotlin.reflect.KVisibility
+import kotlin.reflect.full.declaredMemberProperties
+import kotlin.reflect.full.memberProperties
+
+open class Human(val gender: String)
+
+abstract class Identifiable(open val id: Int)
+class TestClass(val name: String, val age: Int, override val id: Int): Identifiable(id)
+
+class Person(val name: String, val age: Int): Human("male") {
+}
+
+class GetAllFieldsUsingReflectionUnitTest {
+
+    @Test
+    fun `obtain all field names using declaredMemberProperties method`() {
+        val fieldNames =  getAllFieldNamesUsingDeclaredMemberPropertiesMethod(TestClass::class)
+        assertEquals(listOf("age","id", "name"), fieldNames)
+    }
+
+    @Test
+    fun `obtain all field names using member method`() {
+        val fieldNames = getAllFieldNamesUsingMembersProperty(TestClass::class)
+        assertEquals(listOf("age","id", "name"), fieldNames)
+    }
+
+    @Test
+    fun `obtain all field names using java reflection API`() {
+        val fieldNames = getAllFieldNamesUsingJavaReflection(TestClass::class)
+        assertEquals(listOf("name", "age", "id"), fieldNames)
+    }
+
+    @Test
+    fun `obtain all field names using Class members property `() {
+        val fieldNames = getAllFieldNamesUsingClassMemberProperties(TestClass::class)
+        assertEquals(listOf("age","id", "name"), fieldNames)
+    }
+    @Test
+    fun `show difference between declaredMemberProperties and memberProperties property`() {
+        val declaredProperties = getAllFieldNamesUsingDeclaredMemberPropertiesMethod(Person::class)
+        val allProperties = getAllFieldNamesUsingClassMemberProperties(Person::class)
+
+        assertEquals(listOf("age", "name"), declaredProperties)
+        assertEquals(listOf("age", "name", "gender"), allProperties)
+    }
+}
+
+fun getAllFieldNamesUsingDeclaredMemberPropertiesMethod(clazz: KClass<*>): List<String> {
+    return clazz.declaredMemberProperties
+        .map { it.name }
+}
+fun getAllFieldNamesUsingJavaReflection(clazz: KClass<*>): List<String> {
+    return clazz.java.declaredFields
+        .map { it.name }
+}
+
+fun getAllFieldNamesUsingMembersProperty(clazz: KClass<*>): List<String> {
+    return clazz.members
+        .filter { it is KProperty<*> }
+        .map { it.name }
+}
+fun getAllFieldNamesUsingClassMemberProperties(clazz: KClass<*>): List<String> {
+    return clazz.memberProperties
+        .map { it.name }
+}