Backwards iterator implemented and tested

Author: Pedro David Rodríguez Sánchez

src/main/kotlin/oop/Iterator/BackwardsIterator.kt

@@ -1,5 +1,20 @@
 package oop.Iterator
 
-class BackwardsIterator {
+class BackwardsIterator<T>(list: MutableList<T>): NormalIterator<T>(list) {
+  override fun first(): T? {
+    index = list.size - 1
+    return get()
+  }
 
+  override fun hasNext(): Boolean = index - 1 > -1
+
+  override fun hasPrev(): Boolean = this.list.size > index + 1
+
+  override fun nextIndex(): Int = if(index > -1) index - 1 else -1
+
+  override fun prevIndex(): Int = if(index > this.list.size) index +1 else -1
+
+  override fun next(): T? = if (hasNext()) list[index--] else throw NoSuchElementException()
+
+  override fun prev(): T? = if (hasPrev()) list[index++] else throw NoSuchElementException()
 }

src/main/kotlin/oop/Iterator/NormalIterator.kt

@@ -1,7 +1,7 @@
 package oop.Iterator
 
-class NormalIterator<T>(val list: MutableList<T>) : Iterator<T> {
-  private var index = 0
+open class NormalIterator<T>(val list: MutableList<T>) : Iterator<T> {
+  protected var index = 0
 
   override fun first(): T? {
     index = 0
@@ -18,7 +18,7 @@ class NormalIterator<T>(val list: MutableList<T>) : Iterator<T> {
 
   override fun next(): T? = if (hasNext()) list[index++] else throw NoSuchElementException()
 
-  override fun prev(): T? = if (hasPrev()) list[index++] else throw NoSuchElementException()
+  override fun prev(): T? = if (hasPrev()) list[index--] else throw NoSuchElementException()
 
   override fun set(element: T) {
     list[index] = element

src/main/kotlin/oop/Iterator/RandomIterator.kt

@@ -1,4 +1,5 @@
 package oop.Iterator
 
-class RandomIterator {
+class RandomIterator<T>(list: MutableList<T>): NormalIterator<T>(list) {
+
 }

src/test/kotlin/oop/Iterator/BackwardsIteratorShould.kt

@@ -0,0 +1,26 @@
+package oop.Iterator
+
+
+import org.hamcrest.CoreMatchers.`is`
+import org.hamcrest.MatcherAssert.assertThat
+import org.junit.Test
+
+class BackwardsIteratorShould {
+  private val list = mutableListOf("10", "12", "15", "29", "30", "36")
+  private val iterator: Iterator<String> = BackwardsIterator(list)
+
+  @Test
+  fun `Return last item of collection when call`(){
+    assertThat(iterator.first(),`is`("36"))
+  }
+
+  @Test
+  fun `Iterate list from back to start`(){
+    var res = ""
+    iterator.first()
+    iterator.forEach {
+      res += "$it,"
+    }
+    assertThat(res, `is`("36,30,29,15,12,10,"))
+  }
+}