Some Guava features were really useful for Java 7 application because Guava was bringing APIs missing in the JDK. The introduction of Kotlin and
Java 8+ fixed some of these limitations. When migrating an application to Kotlin and/or using a Java 8+ target, it is recommended to prefer the
provided native APIs over Guava to ease maintenance: developers don’t need to learn how to use two APIs and can stick to the default one.
This rule raises an issue when the Guava APIs listed below are used.
| Guava API |
Kotlin API |
com.google.common.base.Joiner.on
|
kotlin.collections.Iterable.joinToString or kotlin.Array.joinToString
|
com.google.common.base.Predicate
|
Use function with type (T) → Boolean as a replacement for Predicate<T> |
com.google.common.base.Function
|
Use function with type (T) → R as a replacement for Function<T, R> |
com.google.common.base.Supplier
|
Use function with type () → T as a replacement for Supplier<T> |
com.google.common.io.Files.createTempDir
|
kotlin.io.path.createTempDirectory
|
com.google.common.collect.ImmutableSet.of
|
kotlin.collections.setOf
|
com.google.common.collect.ImmutableList.of
|
kotlin.collections.listOf
|
com.google.common.collect.ImmutableMap.of
|
kotlin.collections.mapOf
|
| Guava API |
Java 8 API |
com.google.common.io.BaseEncoding.base64
|
java.util.Base64
|
com.google.common.io.BaseEncoding.base64Url
|
java.util.Base64
|
com.google.common.base.Optional
|
java.util.Optional*
|
com.google.common.base.Optional.of
|
java.util.Optional.of*
|
com.google.common.base.Optional.absent
|
java.util.Optional.empty*
|
com.google.common.base.Optional.fromNullable
|
java.util.Optional.ofNullable*
|
*: Note that this rule will also raise issues for the use of Guava Optional and recommend using the Java 8+ equivalent instead. In
most Kotlin-only cases, you will probably be better off using Kotlin’s null-safe type system directly, without wrapping Optional
constructs. In some cases, such as those involving Java interoperability, it may be necessary to use Optional in Kotlin, however.
