equal() function in Kotlin

Question

I need if two objects are equal() need to print("Equal") if objects are not equal -> "Not equal".I can not find mistake of this codeThis is my code in IntelliJ IDEA As a side note, when we override equals(), it is recommended to also override the hashCode() method. If we don’t do so, equal objects may get different hash-values; and hash based collections, including HashMap, HashSet, and Hashtable do not work properly (see this for more details). We will be covering more about hashCode() in a separate post. References:

internal class Complex(private val re: Double, private val im: Double) { // Overriding equals() to compare two Complex objects fun equals(o: Object): Boolean { // If the object is compared with itself then return true if (o === this) { return true } /* Check if o is an instance of Complex or not "null instanceof [type]" also returns false */if (o !is Complex) { return false } // typecast o to Complex so that we can compare data members val c = o as Complex // Compare the data members and return accordingly return (java.lang.Double.compare(re, c.re) == 0 && java.lang.Double.compare(im, c.im) == 0) } } // Driver class to test the Complex class fun main(args: Array<String>) { val c1 = Complex(12.0, 15.0) val c2 = Complex(10.0, 15.0) if (c1 == c2) { println("Equal ") } else { println("Not Equal ") } }

What is the error show when you hover your mouse over the squiggles? — Samathingamajig
– Samathingamajig, Commented Mar 7, 2022 at 15:38
Object is not a Kotlin data type. === is not a Kotlin operator. — lukas.j
– lukas.j, Commented Mar 7, 2022 at 15:52
@lukas.j That's the Kotlin reference equality operator, which is sensible to use in an equals() implementation, although of course in this case this class can just be a data class. — Tenfour04
– Tenfour04, Commented Mar 7, 2022 at 16:00
In Kotlin, you must always specify override when overriding (or implementing) a superclass/interface method/property — so you should get into the habit of using it. In this case, it would have given error: 'equals' overrides nothing, showing where the problem lies. — gidds
– gidds, Commented Mar 7, 2022 at 20:27

Tenfour04 · Accepted Answer · 2022-03-07 15:58:17Z

In Kotlin, you use Any instead of Object. It will not allow you to test if your class instance is an Object, only Any.

Also, you are failing to override equals since you didn't use the override keyword. The argument needs to be Any?, not Object.

Change

fun equals(o: Object): Boolean {

to

override fun equals(o: Any?): Boolean {

Also, in this case, you should use a data class so you won't have to write your own equals() implementation in the first place.

And in the future, when you aren't using a data class, you can use the IDE option to generate equals and hashcode for you automatically.

lukas.j · Accepted Answer · 2022-03-07 15:47:47Z

A data class would make more sense:

data class Complex( private val re: Double, private val im: Double ) val c1 = Complex(12.0, 15.0) val c2 = Complex(10.0, 15.0) if (c1 == c2) { println("Equal") } else { println("Not Equal") }

Output: Not Equal

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