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I am slightly moving from Java to Kotlin in android app development,
but there are some cases where I don't want to code in Kotlin and want
those particular cases be written in Java:
- It is effort-saving that Kotlin removes extra usage of
findViewByIds
- I know that it is now
null-safety which oppositely Java always triggered with NullPointerException
Lambda expressions are also provided and many other features.
But still, some of my codes cannot be written in Kotlin such as static members or non-primitive fields.
Kotlin annotations actually can replace those static members. But love some coding features of Java and dont want to leave that.
My question is can I combine Java and Kotlin together?
If your question is can you use kotlin files in java files and vice versa then the answer is yes.
If you are asking if you can use kotlin syntax in java files and vice versa then the answer is no.
To use kotlin code in a java class you are simply using the class like any other java class
You can create a java similar static variables using companion object.
You can easily create singleton in Kotlin using object.
After I leant kotlin. I have migrated all my codes to Kotlin.
You can have in your project Java and Kotlin Class and Activities.
The same Class can't have Java and Kotlin.
You can convert a Java file to Kotlin with Ctrl+Alt+Shift+K or just double tap SHIFT and search for Convert Java to Kotlin
Even if it's interop you can't mix Java and Kotlin in the same file.
If you really want to have static methods/variables you can use an companion object. You can also access create a "real" static method in your JVM by using @JvmStatic.
Simple sample is:
companion object {
@JvmStatic
fun newInstance() ) SampleFragment()
}
which equals to
public static SampleFragment() { return new SampleFragment(); }
By using @JvmStatic you can use Java to access your Static methods like before.
