Examples for BAEL-1169 (#3934)

core-kotlin/src/test/kotlin/com/baeldung/kotlin/objects/Counter.kt

@@ -0,0 +1,15 @@
+package com.baeldung.kotlin.objects
+
+object Counter {
+    private var count: Int = 0
+
+    fun currentCount() = count
+
+    fun increment() {
+        ++count
+    }
+
+    fun decrement() {
+        --count
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/objects/ObjectsTest.kt

@@ -0,0 +1,36 @@
+package com.baeldung.kotlin.objects
+
+import org.junit.Assert
+import org.junit.Test
+
+class ObjectsTest {
+    @Test
+    fun singleton() {
+
+        Assert.assertEquals(42, SimpleSingleton.answer)
+        Assert.assertEquals("Hello, world!", SimpleSingleton.greet("world"))
+    }
+
+    @Test
+    fun counter() {
+        Assert.assertEquals(0, Counter.currentCount())
+        Counter.increment()
+        Assert.assertEquals(1, Counter.currentCount())
+        Counter.decrement()
+        Assert.assertEquals(0, Counter.currentCount())
+    }
+
+    @Test
+    fun comparator() {
+        val strings = listOf("Hello", "World")
+        val sortedStrings = strings.sortedWith(ReverseStringComparator)
+
+        Assert.assertEquals(listOf("World", "Hello"), sortedStrings)
+    }
+
+    @Test
+    fun companion() {
+        Assert.assertEquals("You can see me", OuterClass.public)
+        // Assert.assertEquals("You can't see me", OuterClass.secret) // Cannot access 'secret'
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/objects/OuterClass.kt

@@ -0,0 +1,10 @@
+package com.baeldung.kotlin.objects
+
+class OuterClass {
+    companion object {
+        private val secret = "You can't see me"
+        val public = "You can see me"
+    }
+
+    fun getSecretValue() = secret
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/objects/ReverseStringComparator.kt

@@ -0,0 +1,5 @@
+package com.baeldung.kotlin.objects
+
+object ReverseStringComparator : Comparator<String> {
+    override fun compare(o1: String, o2: String) = o1.reversed().compareTo(o2.reversed())
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/objects/SimpleSingleton.kt

@@ -0,0 +1,7 @@
+package com.baeldung.kotlin.objects
+
+object SimpleSingleton {
+    val answer = 42;
+
+    fun greet(name: String) = "Hello, $name!"
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/objects/StaticClass.kt

@@ -0,0 +1,8 @@
+package com.baeldung.kotlin.objects
+
+class StaticClass {
+    companion object {
+        @JvmStatic
+        val staticField = 42
+    }
+}