kotlin data class equals
We already know that we use it to compare strings. AutoValue is a popular solution to this problem in Java.
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For example on JVM KClass instances for a primitive type int and the corresponding wrapper type javalangInteger are considered equal because they have the same fully qualified name kotlinInt.
. Kotlin is protected under the Kotlin Foundation and licensed under the Apache 2 license. Data class Userval name. Kotlin compiler generates hashCode and equals methods for data classes including properties in the constructor only.
All primary constructor parameters need to be marked as val or var. If the classes represent Array then Class objects of their element types are equal. ToString of the form User nameJohn age42.
Structural equality - a check for equals Referential equality - two references point to the same object Structural equality. As an added bonus Kotlin also automatically provides immutability. Kotlins data class is a neat way to represent data models without writing the boilerplate code associated with equals hashCode and toString.
We have described three ways of how to implement equalshashCode for a Kotlin entity. In Kotlin this type of class is known as data class and is marked as data. Returns true when two objects have the same content.
Returns the hashcode value of the object. See the de-compiled code. Val list1 listOf1 2 3 val list2 listOf1 2 3 val array1 arrayOf1 2 3 val array2 arrayOf1 2 3 Side note.
如果超类型具有 open 的 componentN 函数并且返回兼容的类型 那么会为数据类生成相应的函数并覆盖超类的实现. Equals and hashCode toString of the form Book nameJournalDev authorNameAnupam componentN functions for each of the parameters in the order specified. The equals method is related to comparing objects.
In the POJO class we just create fields and settergetter methods to set and retrieve data from is Object. Any members declared with val instead of var become immutable and no setters are generated for them. The operator works for standard data types such as Int or Double as we would expect it to.
Data class in Kotlin Data Class In Kotlin In domain-driven design development simple class as bean or POJO or model class in Java. 在 Kotlin 中这叫做 数据类 并标记为 data. Object Equality Comparing objects class instances in Kotlin is a little different than Java and very similar to Scala.
Kotlin data classes are useful for this purpose The compiler automatically generates the following functions for data classes. Defines a data class with the data modifier. Asserts that the expected value is equal to the actual value with an optional message.
In Kotlin these are called data classes and are marked with data. Equals and hashCode methods a useful toString method a copy function that is useful in an update as you copy scenario. This is known as destructuring declarations.
Method toString is auto-generated which makes println output look nice. Data class in Kotlin provide default implementation of toString equals and hashCode functions without explicit declaration. Key points calls equals under the hood structural equality is used to test reference equality Classes dont have equals or hashCode methods by default you need to implement them.
In Kotlin its a language feature. The primary constructor needs to have at least one parameter. In Kotlin equals behaves differently between List and Array as you can see from code below.
Example of a data. Int The compiler automatically derives the following members from all properties declared in the primary constructor. We can use this function to copy an object and modify its value.
However when we try to compare 2 objects using well get true only if were comparing 2 references to the same object. Int The compiler automatically derives the following functions. In Kotlin there are two types of equality.
ToString The default implementation of the toString method would return the output in the following format. There are following conditions for a Kotlin class to be defined as a Data Class. Kotlin Data class automatically creates the following functions for you.
Data class instances with exactly matching attributes have the same hashCode. Returns an object as a readable string. In such classes some standard functions are often derivable from the data.
Kotlin data class. Kotlin Data Class built-in methods. Override the default equals method by declaring users equal if they have the same id.
Using ab is the same as aequalsb val areListsEqual list1 list2 true val areArraysEqual array1 array2 false. A Kotlin Data Class is used to hold the data only and it does not provide any other functionality apart from holding data. The property name in PersonImpl1 is not included in the hashCode equals hence the difference.
Lets understand these concepts with the help of an example. The kotlin data class is one of the types and features for to hold the user input data and state in such cases we use some standard functions for to derive the datas which is enable to ensure consistency and it is a meaningful behavior for to generate codes it has the primary constructor which helps and needs to pass have at least one parameter. Data class Studentval name.
Our custom equals considers two instances equal if their ids are equal. Hashcode implementation of PersonImpl1 public int hashCode long tmp4_1 thisid. The Data class comes with a handful of other functions.
Equals hashCode pair. The reason for that is because data class automatically generates wrong implementation for equalshashCode that do not follow the contract. By convention an expression like a b is translated to.
You get it for free. In Kotlin exactly same as simple POJO class with data keyword. Personally I dont recommend to use a data class for an entity.
Structural equality is checked by the operation and its negated counterpart. For data classes Kotlin automatically generates getters setters equals hashCode a human-readable toString and even a copy method.
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