add tasks for objects and companion objects

src/i_introduction/_13_Object_And_Companion_Object/n13Objects.kt

@@ -0,0 +1,28 @@
+package i_introduction._13_Object_And_Companion_Object
+
+import util.doc13
+
+fun todoTask13(): Nothing = util.TODO(
+        """
+        Task 13.
+        Kotlin supports creating thread-safe singletons, which can be useful in various situations.
+        You can declare them using object keyword.
+        When You want to use declared object, You don't need to add initializer.
+        `val example = ObjectExample`
+
+        Add `init { }` block, where You will increment `counterForCreation` property, and
+        implement getter for `counterForGetter`, which should return it and increment by one.
+        """,
+        documentation = doc13()
+)
+
+object ObjectExample {
+    var counterForCreation = 0
+        private set
+
+    var counterForGetter = 0
+        get() = todoTask13()
+        private set
+}
+
+

src/i_introduction/_13_Object_And_Companion_Object/n14CompanionObject.kt

@@ -0,0 +1,24 @@
+package i_introduction._13_Object_And_Companion_Object
+
+import util.doc14
+
+fun todoTask14(): Nothing = util.TODO(
+        """
+        Task 14.
+        Similar behaviour have companion object.
+        It needs to be declared inside class and can implement interfaces or extends classes.
+        They can be use ie. for fabric method.
+        When integrating with Java code, sometimes We need to declare static functions, which We don't have in Kotlin.
+        Then We can use annotation `@JvmStatic`, but it can be use only inside objects on properties
+        or in companion objects on both functions ad properties.
+
+        Add companion object inside class below with property.
+        Make function `getCounter()` return it and increment by one.
+        """,
+        documentation = doc14()
+)
+
+class ExampleForCompanionObject {
+
+    fun getCounter(): Int = todoTask14()
+}

src/util/LinksToDocumentation.kt

@@ -61,6 +61,18 @@ fun doc11() {}
  */
 fun doc12() {}
 
+/**
+ * @see <a href="https://kotlinlang.org/docs/reference/classes.html#constructors">Class constructors</a>,
+ * <a href="https://kotlinlang.org/docs/reference/object-declarations.html#object-declarations">Object declarations</a>
+ */
+fun doc13() {}
+
+/**
+ * @see <a href="https://kotlinlang.org/docs/reference/object-declarations.html#object-declarations">Object declarations</a>,
+ * <a href="https://kotlinlang.org/docs/reference/java-to-kotlin-interop.html#static-fields">Static fields in java integrations</a>
+ */
+fun doc14() {}
+
 /**
  * @see <a href="https://kotlinlang.org/docs/reference/operator-overloading.html">Operator overloading</a>
  */

test/i_introduction/_13_Object_And_Companion_Object/n13ObjectsKtTest.kt

@@ -0,0 +1,22 @@
+package i_introduction._13_Object_And_Companion_Object
+
+import org.junit.Assert.assertThat
+import org.junit.Test
+import org.hamcrest.core.Is.`is` as isEqualTo
+
+class n13ObjectsKtTest {
+
+    @Test fun checkNumberOfInitialisations() {
+        val objectExample = ObjectExample
+
+        assertThat(objectExample.counterForCreation, isEqualTo(1))
+        assertThat(objectExample.counterForGetter, isEqualTo(0))
+        assertThat(objectExample.counterForGetter, isEqualTo(1))
+
+        val secondInit = ObjectExample
+        assertThat(secondInit.counterForCreation, isEqualTo(1))
+        assertThat(secondInit.counterForGetter, isEqualTo(2))
+
+        assertThat(objectExample.hashCode(), isEqualTo(secondInit.hashCode()))
+    }
+}

test/i_introduction/_13_Object_And_Companion_Object/n14CompanionObjectKtTest.kt

@@ -0,0 +1,22 @@
+package i_introduction._13_Object_And_Companion_Object
+
+import org.hamcrest.core.IsNot.not
+import org.hamcrest.core.Is.`is` as isEqualTo
+import org.junit.Assert.assertThat
+import org.junit.Test
+
+class n14CompanionObjectKtTest {
+
+    @Test
+    fun checkNumberOfInitialisations() {
+        val objectExample = ExampleForCompanionObject()
+
+        assertThat(objectExample.getCounter(), isEqualTo(0))
+        assertThat(objectExample.getCounter(), isEqualTo(1))
+
+        val secondInit = ExampleForCompanionObject()
+        assertThat(secondInit.getCounter(), isEqualTo(2))
+
+        assertThat(objectExample.hashCode(), not(isEqualTo(secondInit.hashCode())))
+    }
+}