Kotlin program | Example of Secondary Constructor

Kotlin | Secondary Constructor: Here, we are implementing a Kotlin program to demonstrate the example of secondary constructor.
Submitted by IncludeHelp, on June 12, 2020

Secondary Constructor

Kotlin class can also declare, Secondary Constructor in the class body, Prefixed with constructor keyboard
If the class has a primary constructor then each secondary constructor needs to delegate primary constructor.
Delegation of another constructor of the same class is done using the 'this' keyword.
NOTE: Delegation to the primary constructor happens as the first statement of a secondary constructor and code in initializer blocks effectively becomes part of the primary constructor, so all initializer blocks and property initializer is executed before the secondary constructor body.
If Kotlin class has no primary constructor, the delegation still happens implicitly, and the initializer blocks are still executed

Program to demonstrate the example of Secondary Constructor in Kotlin

package com.includehelp

// Declared Class with Parameterized 
// primary constructor
class Animal(name:String){
    // Property Declaration
    private var name: String?=null
    private var type: String?=null

    // Init Block, effectively becomes part of 
    // the primary constructor
    init{
        this.name=name
        println("Init Block")
    }

    // Secondary Constructor, calls/delegates the 
    // primary constructor using 'this'
    constructor(name:String,type:String) : this(name){
        this.type=type
        println("Secondary Constructor")
    }

    //fun to print class property data
    fun printData(){
        println("Animal -> Name : $name  and Type : $type")
    }
}

// Declared class without primary Constructor, 
// delegation still happens implicitly,
// and the initializer blocks are still executed 
// before Secondary Constructor execution
class Sample{
    // First Init Block
    init{
        println("Init Block 1")
    }

    // Secondary Constructor
    constructor(a: Int,b:Int){
        println("Secondary Constructor : A=$a and B=$b")
    }

    // Second Init block
    init {
        println("Init Block 2")
    }
}

// Main function, Entry Point of Program
fun main(args: Array<String>){
    // Create Class object to call Primary constructor 
    // of Animal Class
    val animal = Animal("Cobra")
    animal.printData()

    // Create Class object to call Secondary constructor 
    // of Animal Class
    val animal2 = Animal("Python","Snake")
    animal2.printData()

    // Create Class object to call Secondary constructor 
    // of Sample Class with named parameter
    Sample(a=10, b=20)
}

Output:

Init Block
Animal -> Name : Cobra  and Type : null
Init Block
Secondary Constructor
Animal -> Name : Python  and Type : Snake
Init Block 1
Init Block 2
Secondary Constructor : A=10 and B=20

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