There is no error in the code. But after install, my app crash and rectifying logcat "error is attemp to write to null array"

Question

Here is my code Plane.kt

 init {
    plane[0] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_1)
    plane[1] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_2)
    plane[2] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_3)
    plane[3] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_4)
    plane[4] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_5)
    plane[5] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_6)
    plane[6] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_7)
    plane[7] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_8)
    plane[8] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_9)
    plane[9] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_10)
    plane[10] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_11)
    plane[11] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_12)
    plane[12] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_13)
    plane[13] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_14)
    plane[14] = BitmapFactory.decodeResource(context.resources, R.drawable.plane_15)
    random = Random()
    resetPosition()
}

Here is my code Plane2.kt

open class Plane2(context: Context) : Plane(context) {
override var  plane = arrayOfNulls<Bitmap>(10)
override val bitmap: Bitmap?
    get() = plane[planeFrame]

override val width: Int
    get() = plane[0]!!.width

override val height: Int
    get() = plane[0]!!.height

override fun resetPosition() {
    planeX = -(200 + random.nextInt(1500))
    planeY = random.nextInt(400)
    velocity = 5 + random.nextInt(21)
}

Here is my code GameView.kt

 init {
    tank = BitmapFactory.decodeResource(resources, R.drawable.tank)
    val display = (getContext() as Activity).windowManager.defaultDisplay
    val size = Point()
    display.getSize(size)
    dWidth = size.x
    dHeight = size.y
    rect = Rect(0, 0, dWidth, dHeight)
    planes = ArrayList()
    planes2 = ArrayList()
    missiles = ArrayList()
    explosions = ArrayList()
    for (i in 0..1) {
  open class Plane2(context: Context) : Plane(context) {
override var  plane = arrayOfNulls<Bitmap>(10)
override val bitmap: Bitmap?
    get() = plane[planeFrame]

override val width: Int
    get() = plane[0]!!.width

override val height: Int
    get() = plane[0]!!.height

override fun resetPosition() {
    planeX = -(200 + random.nextInt(1500))
    planeY = random.nextInt(400)
    velocity = 5 + random.nextInt(21)
}
  val plane = Plane(context)
        planes.add(plane)
        val plane2 = Plane2(context)
        planes2.add(plane2)
    }

StartGame.kt

class StartGame : Activity() {
var gameView: GameView? = null
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    requestWindowFeature(Window.FEATURE_NO_TITLE)
    this.window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN)
    this.window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
    //gameView = GameView(this)
    gameView = GameView(this)
    setContentView(gameView)
}

}

Here is my Logcat error

2019-12-31 01:58:49.006 6311-6311/com.example.shooterplane E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.shooterplane, PID: 6311
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.shooterplane/com.example.shooterplane.StartGame}: java.lang.NullPointerException: Attempt to write to null array
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1831)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:201)
    at android.app.ActivityThread.main(ActivityThread.java:6810)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
 Caused by: java.lang.NullPointerException: Attempt to write to null array
    at com.example.shooterplane.Plane.<init>(Plane.kt:32)
    at com.example.shooterplane.Plane2.<init>(Plane2.kt:7)
    at com.example.shooterplane.GameView.<init>(GameView.kt:183)
    at com.example.shooterplane.StartGame.onCreate(StartGame.kt:16)
    at android.app.Activity.performCreate(Activity.java:7224)
    at android.app.Activity.performCreate(Activity.java:7213)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2926)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1831) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:201) 
    at android.app.ActivityThread.main(ActivityThread.java:6810) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873) 

What is the logic of this problem?

Answer 1

Looks like you didn't initialize the plane array in Plane.kt:

init {
    plane = arrayOf(
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_1),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_2),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_3),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_4),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_5),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_6),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_7),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_8),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_9),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_10),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_11),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_12),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_13),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_14),
        BitmapFactory.decodeResource(context.resources, R.drawable.plane_15)
    )
    random = Random()
    resetPosition()
}