More progress on part 2

Signed-off-by: Harsh Shandilya <msfjarvis@gmail.com>

content/posts/teachingkotlin-part-2-variables.md

@@ -7,3 +7,93 @@ tags = ["android", "teachingkotlin", "kotlin"]
 title = "#TeachingKotlin Part 2 - Variables"
 
 +++
+
+Even the variables in Kotlin are supercharged!
+
+Let's start with a simple [data class](https://kotlinlang.org/docs/reference/data-classes.html#data-classes) and see how the variables in there behave.
+
+``` kotlin
+data class Student(val name: String, val age: Int, val subjects: ArrayList<String>)
+```
+
+To use the variables in this class, Kotlin let's you directly use the dot notation for accessing.
+
+``` kotlin
+
+>>> val s1 = Student("Keith Hernandez", 21, arrayListOf("Mathematics", "Social Studies"))
+>>> println(s1.name)
+
+Keith Hernandez
+
+>>> println(s1) // data classes automatically generate `toString` and `hashCode` 
+
+Student(name=Keith Hernandez, age=21, subjects=[Mathematics, Social Studies])
+```
+
+For Java callers, Kotlin also generates getters and setter methods.
+
+``` java
+final Student s1 = new Student("Keith Hernandez", 21, arrayListOf("Mathematics", "Social Studies"));
+System.out.println(s1.getName());
+System.out.println(s1);
+```
+
+The same properties apply to variables in non-data classes as well.
+
+``` kotlin
+
+>>> class Item(id: Int, name: String) {
+
+...     val itemId = id
+...     val itemName = name
+... }
+
+>>> val item = Item(0, "Bricks")
+>>> println(item.itemId)
+
+0
+
+>>> println(item)
+
+Line_4$Item@46fb460a
+
+>> >
+
+```
+
+As you can notice, the `toString` implementation is not identical to our data classes but that's a topic for another post. Back to variables!
+
+## Customising getters and setters
+
+While Kotlin creates getters and setters automatically, we can customize their behaviour.
+
+``` kotlin
+class Item(id: Int, name: String) {
+    var itemId = id
+    var itemName = name
+    var currentState: Pair<Int, String> = Pair(itemId, itemName)
+        set(value) {
+            itemId = value.first
+            itemName = value.second
+            field = value
+        }
+    override fun toString() : String {
+        return "id=$itemId,name=$itemName"
+    }
+}
+```
+
+Let's take this for a spin in the Kotlin REPL and see how our `currentState` field behaves.
+
+```kotlin
+>>> val item = Item(0, "Nails")
+>>> println(item)
+id=0,name=Nails
+>>> item.currentState = Pair(1, "Bricks")
+>>> println(item)
+id=1,name=Bricks
+```
+
+Notice how setting a new value to currentState mutates the other variables as well? That's because of our custom setter. These setters are identical to a normal top-level function except a reference to the field in question is available as the variable `field` for manipulation.
+
+## Visiblity modifiers