kotlin data class equals
The equals method is related to comparing objects. Wir erstellen oft Klassen um einige Daten darin zu halten.
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In FP you create classes just to hold data like structs in C.
. The compiler automatically generates the following functions for data classes. The equals method. Using ab is the same as aequalsb val areListsEqual list1 list2 true val areArraysEqual array1 array2 false.
Tests if values are identical tests if they should be considered as equivalent instances in some way. Int The compiler automatically derives the following functions. In Kotlin its a language feature.
The third sense is as an ordering eg as used with etc. Data class Userval name. Its easy to assume that equals will just work but digging a little deeper can help avoid subtle bugs.
Val list1 listOf1 2 3 val list2 listOf1 2 3 val array1 arrayOf1 2 3 val array2 arrayOf1 2 3 Side note. You get it for free. Comparing objects class instances in Kotlin is a little different than Java and very similar to Scala.
Data class Studentval name. The reason for that is because data class automatically generates wrong implementation for equalshashCode that do not follow the contract. Int Good thing about Kotlin Data Class is that when you declare a Kotlin Data Class the compiler generates Constructor toString.
Kotlin Data Class built-in methods. This is known as destructuring declarations. However when we try to compare 2 objects using well get true only if were comparing 2 references to the same object.
The property name in PersonImpl1 is not included in the hashCode equals hence the difference. Its simple to define a Kotlin Data Class. We have described three ways of how to implement equalshashCode for a Kotlin entity.
See the de-compiled code. Hashcode implementation of PersonImpl1 public int hashCode long tmp4_1 thisid. Kotlin compiler generates hashCode and equals methods for data classes including properties in the constructor only.
In Kotlin these are called data classes and are marked with data. Classes dont have equals or hashCode methods by default you need to implement them. We already know that we use it to compare strings.
In Kotlin wird dieser Klassentyp als Datenklasse bezeichnet und als data gekennzeichnet. 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 which is all have the primary. Equals hashCode pair.
在 Kotlin 中这叫做 数据类 并标记为 data. Equal even though aequalsb might not. Personally I dont recommend to use a data class for an entity.
Kotlin compiler provides more benefits using data keyword. Lets understand these concepts with the help of an example. In solchen Klassen sind oft einige Standardfunktionen aus den Daten ableitbar.
In such classes some standard functions are often derivable from the data. Equals and hashCode toString of the form Book nameJournalDev authorNameAnupam componentN functions for each of the parameters in the order specified. 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.
Key points calls equals under the hood structural equality is used to test reference equality. String val age. Kotlin data class.
In Kotlin equals behaves differently between List and Array as you can see from code below. Structural equality - a check for equals Referential equality - two references point to the same object Structural equality. Data class Userval name.
The operator works for standard data types such as Int or Double as we would expect it to. For data classes Kotlin automatically generates getters setters equals hashCode a human-readable toString and even a copy method. In Kotlin this type of class is known as data class and is marked as data.
Structural equality is checked by the operation and its negated counterpart. Kotlin Data class automatically creates the following functions for you. The first could give case-blind comparisons for example where the.
AutoValue is a popular solution to this problem in Java. In Kotlin exactly same as simple POJO class with data keyword. In Kotlin there are two types of equality.
There are three sorts of equality. A copy function that is useful in an update as you copy scenario. A useful toString method.
ToString of the form User nameJohn age42. Any members declared with val instead of var become immutable and no setters are generated for them. By convention an expression like a b is translated to.
ToString The default implementation of the toString method would return the output in the following format. A data class generates the equals function compare is not generated based on the properties that are declared in the primary constructor so if you want it not to compare the IDs youll have to move the ID property out of the primary constructor. In domain-driven design development simple class as bean or POJO or model class in Java.
If a Kotlin class is marked with data keyword then it becomes a data class. Kotlins data class is a neat way to represent data models without writing the boilerplate code associated with equals hashCode and toString. Kotlins solution makes sense.
As an added bonus Kotlin also automatically provides immutability. Data class in Kotlin provide default implementation of toString equals and hashCode functions without explicit declaration. Kotlin data classes are useful for this purpose.
In the POJO class we just create fields and settergetter methods to set and retrieve data from is Object. Int The compiler automatically derives the following members from all properties declared in the primary constructor. Example of a data.
For example on JVM KClass instances for a primitive type int and the corresponding wrapper type javalangInteger are considered equal because they have. Data class Bookval name. If the classes represent Array then Class objects of their element types are equal.
Equals and hashCode methods.
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