Memo for migration from java to kotlin

** Introduction **

Kotlin has become the official language of Android, and it seems that we will develop more with kotlin from now on. I had the opportunity to replace some java classes with kotlin at work Make a note of how you fixed the parts that did not work with batch replacement. Since Android development is still in its first year, please understand that there may be some parts that cannot be reached.

reference

https://www.slideshare.net/kenichitatsuhama/java-kotlin

What i did

** Perform batch replacement **

First, select convert Java File to Kotlin File from the Code menu.

Mostly it will replace it well.

** Correct the description after return @ ~ **

Basic return is used when exiting a method It seems that if it is written in lambda, it will not correctly judge whether to exit the method or lambda. If you type @ after return, the correct one will come out as a candidate.

** Add @JvmStatic to static method **

This is a fix to allow java to access kotlin's static methods.

** Take the member variable m **

If you rename it with the function of the IDE, there is no mistake than manual work, so use it.

** Correct any description of "!!" in the member call **

This will be done even if the member is null, so fix it. There are the following methods.

• Change the variable you are passing to Not Null
• Make a Null safe call

** Modify so that variables with "!!" are not passed as function arguments **

• Use scope function to ensure non-Null

Before correction.kt

hoge.fuga(piyo!!)

Revised.kt

piyo?.let {
hoge.fuga(it)
}

** Change to lazy property where @BindDrawable is used **

Example.kt

internal val icon: Drawable? by lazy {
ResourcesCompat.getDrawable(resources, R.drawable.icon, null)
}

** Explicitly specify and convert **

Before correction.kt

bundle.getLong(hogehoge) != 0)

Revised.kt

bundle.getLong(hogehoge) != 0L)

** Change var to val where possible **

I think that it is possible to take measures such as delay initialization using the lazy property for parts that are initialized by onCreate etc.

** Internal will be fully published in the same module, so make it private if you don't need it **

internal -> private

** Change as to as? If necessary **

The part where findFragmentByTag is done, etc.

** Singleton is not automatically converted **

Replace with a singleton using the object keyword

** Unused parameters in lambda expressions are renamed or removed with "_" **

We also refactored this time.

at the end

There seems to be other corrections, but that's all for this time. In addition, I will update it when new corrections come out.