Mastering High Performance with Kotlin

Data classes

Let's decompile our ImmutableKey to Java. The first lines look as follows:

final class ImmutableKey {   @Nullable   private final String name;   @Nullable   public final String getName() {      return this.name;   }   public ImmutableKey(@Nullable String name) {      this.name = name;   }....................

In the preceding snippet, we can see that the ImmutableKey class contains the name field with a getter and a constructor. The name field is marked with the final modifier; thus, it's initialized when a new instance is created, and after this, its value can't be changed.

The decompiled ImmutableKey also overrides a version of the toString method:

public String toString() {   return "ImmutableKey(name=" + this.name + ")";}

The ImmutableKey method also ...