Between execution of left != null and queue.add(left) another thread could have changed the value of left to null. To work around this you have several options. Here are some: Use a local variable with smart cast: val node = left if (node != null) { queue.add(node) } Use a safe call such as one … Read more
This is working code. It wakes CPU every 10 minutes until the phone turns off. Add to Manifest.xml: … <uses-permission android:name=”android.permission.WAKE_LOCK”></uses-permission> … <receiver android:process=”:remote” android:name=”.Alarm”></receiver> … Code in your class: package yourPackage; import android.app.AlarmManager; import android.app.PendingIntent; import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.os.PowerManager; import android.widget.Toast; public class Alarm extends BroadcastReceiver { @Override public void … Read more
consts are compile time constants. Meaning that their value has to be assigned during compile time, unlike vals, where it can be done at runtime. This means, that consts can never be assigned to a function or any class constructor, but only to a String or primitive. For example: const val foo = complexFunctionCall() //Not … Read more
Here are the significant differences between lateinit var and by lazy { … } delegated property: lazy { … } delegate can only be used for val properties, whereas lateinit can only be applied to vars, because it can’t be compiled to a final field, thus no immutability can be guaranteed; lateinit var has a … Read more
As @Vadzim said, in IntelliJ or Android Studio, you just have to do the following to get java code from kotlin: Menu > Tools > Kotlin > Show Kotlin Bytecode Click on the Decompile button Copy the java code Update: With a recent version (1.2+) of the Kotlin plugin you also can directly do Menu … Read more
If you don’t know the main activity, then the package name can be used to launch the application. Intent launchIntent = getPackageManager().getLaunchIntentForPackage(“com.package.address”); if (launchIntent != null) { startActivity(launchIntent);//null pointer check in case package name was not found }
Try: import android.os.Vibrator; … Vibrator v = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE); // Vibrate for 500 milliseconds if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) { v.vibrate(VibrationEffect.createOneShot(500, VibrationEffect.DEFAULT_AMPLITUDE)); } else { //deprecated in API 26 v.vibrate(500); } Note: Don’t forget to include permission in AndroidManifest.xml file: <uses-permission android:name=”android.permission.VIBRATE”/>
In Kotlin, if statements are expressions. So the following code is equivalent: if (a) b else c The distinction between expression and statement is important here. In Java/C#/JavaScript, if forms a statement, meaning that it does not resolve to a value. More concretely, you can’t assign it to a variable. // Valid Kotlin, but invalid … Read more
There is a lateinit improvement in Kotlin 1.2 that allows to check the initialization state of lateinit variable directly: lateinit var file: File if (this::file.isInitialized) { … } See the annoucement on JetBrains blog or the KEEP proposal. UPDATE: Kotlin 1.2 has been released. You can find lateinit enhancements here: Checking whether a lateinit var … Read more
app/build.gradle android { … compileOptions { sourceCompatibility JavaVersion.VERSION_1_8 targetCompatibility JavaVersion.VERSION_1_8 } kotlinOptions { jvmTarget = JavaVersion.VERSION_1_8.toString() } } GL Use Java 8 language features