Creating instances without new keyword in Kotlin - Visual Walkthrough

Concept Flow - Creating instances without new keyword

Class Definition

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Call Constructor

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Instance Created

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Use Instance

In Kotlin, you create an instance by calling the class name like a function, without using the 'new' keyword.

Execution Sample

Kotlin

class Person(val name: String)

fun main() {
    val p = Person("Anna")
    println(p.name)
}

This code creates a Person instance named Anna without using 'new' and prints the name.

Execution Table

Step	Action	Code Line	Result
1	Define class Person with property name	class Person(val name: String)	Class Person ready
2	Call Person constructor with "Anna"	val p = Person("Anna")	Instance p created with name = "Anna"
3	Print p.name	println(p.name)	Output: Anna
4	Program ends	}	Execution complete

💡 Reached end of main function, program stops

Variable Tracker

Variable	Start	After Step 2	Final
p	null	Person(name="Anna")	Person(name="Anna")

Key Moments - 2 Insights

Why don't we use 'new' to create an instance in Kotlin?

Kotlin simplifies instance creation by calling the class name directly as a function, as shown in step 2 of the execution_table.

How does Kotlin know to create an instance when we write Person("Anna")?

Person("Anna") calls the primary constructor of the class Person, which creates the instance, as seen in step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of variable 'p' after step 2?

A null

B Person instance with name "Anna"

C String "Anna"

D Undefined

💡 Hint

Check variable_tracker row for 'p' after step 2

At which step does the program print the output?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' and 'Result' columns in execution_table

If we change the code to val p = Person("Bob"), what changes in the execution_table?

A Step 1 changes

B Step 3 output remains "Anna"

C Step 2 result changes to name = "Bob"

D No changes at all

💡 Hint

Focus on the 'Result' column in step 2 and step 3 of execution_table

Concept Snapshot

Kotlin creates instances by calling the class name like a function.
No 'new' keyword is needed.
Syntax: val obj = ClassName(args)
This calls the constructor and returns the instance.
Use instance properties or methods with dot notation.

Full Transcript

In Kotlin, you create an instance of a class by calling the class name with parentheses and arguments, without using the 'new' keyword. For example, val p = Person("Anna") creates a new Person object with the name Anna. The program then can use this instance, like printing p.name. This is simpler than some other languages that require 'new'. The execution steps show defining the class, creating the instance, printing the name, and ending the program. The variable tracker shows how 'p' changes from null to the new Person instance. This method is clear and concise for beginners.