Checking for equality in Kotlin

For future students on the course "Kotlin Backend Developer" we prepared a translation of useful material.



We also invite you to watch the open lesson on the topic "Kotlin multiplatform: Front / Back in one language".

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There are three ways to check for equality in Kotlin language:

The first way is to compare structures (==)

Operator ==



in Kotlin allows you to compare data contained in variables. However, in Java, this operator is used to compare references of two variables.

In the case of custom classes, ==



it can be used to compare the contents of data classes. Otherwise, this operator compares references.

The second way is comparing links (===)

An operator ===



in Kotlin is used to compare references of two variables. However, in the case of primitives, it ===



is equivalent ==



, that is, it checks the values.

The third way is the method equals

This method equals



performs the same function in Kotlin as ==



.

equals



==



Float



Double



. Float



Double



==



 IEEE 754, equals



, equals



, :

• NaN ;

  
  
  
  
  

• NaN , , POSITIVE_INFINITY
  
  
  
  ;

  
  
  
  
  

• 0,0 , 0,0.

  
  
  
  
  

, , .

1.

val firstInt = 5
val secondInt = 5

println(firstInt == secondInt)  // true
println(firstInt === secondInt) // true
println(firstInt.equals(secondInt)) // true
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

.

2.

val firstInt = Integer(5)
val secondInt = Integer(5)
println(firstInt == secondInt)  // true
println(firstInt === secondInt) // false
println(firstInt.equals(secondInt)) // true
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

firstInt



secondInt



. (===



) false



. equals



. , true



, 5



.

3.

class Student(val name : String)

val student1 = Student(“Jasmeet”)
val student2 = Student(“Jasmeet”)

println(student1 === student2) // false
println(student1 == student2) // false
println(student1.equals(student2)) // false
println(student1.name === student2.name) // true
println(student1.name == student2.name) // true
println(student1.name.equals(student2.name)) // true
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

student



, , , . , Java.

, data-.

data class Student(val name : String)

val student1 = Student(“Jasmeet”)
val student2 = Student(“Jasmeet”)

println(student1 === student2) // false
println(student1 == student2) // true
println(student1.equals(student2)) // true
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

4.

val negativeZero = -0.0f
val positiveZero = 0.0f

println(negativeZero == positiveZero) // true
println(negativeZero.equals(positiveZero)) // false
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, ==



IEEE 754. true



. equals



, false



.

: https://kotlinlang.org/docs/reference/equality.html

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"Kotlin Backend Developer".

"Kotlin multiplatform: Front/Back ".

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