Object expressions (anonymous objects) in Kotlin - Step-by-Step Execution

Concept Flow - Object expressions (anonymous objects)

Start

↓

Create anonymous object

↓

Initialize properties

↓

Call methods

↓

Use object

↓

End

This flow shows how Kotlin creates an anonymous object, initializes it, and uses its properties and methods immediately.

Execution Sample

Kotlin

val obj = object {
    val x = 10
    fun greet() = "Hi"
}
println(obj.x)
println(obj.greet())

Creates an anonymous object with a property and a method, then prints them.

Execution Table

Step	Action	Evaluation	Result
1	Create anonymous object	object { val x=10; fun greet() = "Hi" }	Object created with x=10 and greet()
2	Initialize property x	x = 10	x is set to 10
3	Define method greet()	fun greet() = "Hi"	Method greet() ready
4	Assign object to variable obj	val obj = object {...}	obj references the anonymous object
5	Call obj.x	obj.x	10
6	Call obj.greet()	obj.greet()	"Hi"

💡 All properties and methods accessed; program ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
obj	null	object created	x=10 set	greet() defined	obj references object with x=10 and greet()

Key Moments - 2 Insights

Why can we access obj.x and obj.greet() even though the object has no class name?

Because the object expression creates an anonymous object with properties and methods accessible through the variable obj, as shown in steps 4-6 of the execution_table.

Is the anonymous object reusable or only created once?

The anonymous object is created once when assigned to obj (step 4). It is not reusable like a class but can be used via obj as long as it exists.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of obj.x at step 5?

A null

B 10

C "Hi"

D Undefined

💡 Hint

Check step 5 in execution_table where obj.x is called and returns 10.

At which step is the greet() method defined in the anonymous object?

A Step 2

B Step 4

C Step 3

D Step 6

💡 Hint

Look at step 3 in execution_table where greet() is defined.

If we add a new property y = 20 inside the object, which step would change?

A Step 2

B Step 3

C Step 5

D Step 6

💡 Hint

Adding a property affects initialization steps, see step 2 where x is initialized.

Concept Snapshot

Object expressions create anonymous objects on the spot.
Syntax: val obj = object { val x = 10; fun greet() = "Hi" }
Use obj.property or obj.method() to access.
No class name needed.
Good for quick, one-time objects.

Full Transcript

This example shows how Kotlin creates an anonymous object using an object expression. The object has a property x set to 10 and a method greet() returning "Hi". The object is assigned to the variable obj. We then access obj.x and obj.greet() to get 10 and "Hi" respectively. The execution table traces each step: creating the object, initializing properties, defining methods, assigning to obj, and calling members. The variable tracker shows obj starting as null and ending referencing the anonymous object. Key moments clarify why we can use obj.x and obj.greet() even without a class name, and that the object is created once. The quiz tests understanding of values at steps and effects of adding properties. The snapshot summarizes the concept simply.