android - NullPointerException when trying to access inherited field -

i`m getting npe when trying access overridden variable in parent class

java.lang.nullpointerexception: attempt length of null array @ app.deadmc.materiallivewallpaper.model.square.<init>(square.kt:29) @ app.deadmc.materiallivewallpaper.model.cube.<init>(cube.kt:8) @ app.deadmc.materiallivewallpaper.renderer.materialrenderer.onsurfacecreated(materialrenderer.kt:40) @ android.opengl.glsurfaceview$glthread.guardedrun(glsurfaceview.java:1548) @ android.opengl.glsurfaceview$glthread.run(glsurfaceview.java:1286) 

i show simplified code undestanding problem

i have class drawing square

open class square(renderer: readyrenderer) {     val coords_per_vertex = 3      open val trianglecoords = floatarrayof(             //first triangle             -1.0f, 1.0f, 0.0f, -1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f,             //second triangle             -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f)      private val vertexcount:int = trianglecoords.size / coords_per_vertex      init {         val bb = bytebuffer.allocatedirect(                 trianglecoords.size * 4)         //other code     } } 

square works correctly, want draw cube, inherit square , add more coordinates

open class cube(renderer: readyrenderer):square(renderer) {         val size = 1.0f     override val trianglecoords = floatarrayof(             //front side             // triangle 1             -size, size, size, // top-left             -size, -size, size, // bottom-left             size, -size, size, // bottom-right             // triangle 2             size, -size, size, // bottom-right             size, size, size, // top-right             -size, size, size, // top-left         //and side, left, top, right same way ) } 

seems logic, right? variables have values , there should no place npe.

but when try create instance of cube

 val cube = cube(this@materialrenderer) 

i catch nullpointerexception in square class @ line:

private val vertexcount:int = trianglecoords.size / coords_per_vertex 

even if assign value directly

private val vertexcount:int = 2 

i npe @ square class inside init block @ line:

val bb = bytebuffer.allocatedirect(         trianglecoords.size * 4) 

so have 2 questions:

1. how can fix , still use inheritance?

2. supposed work way?

if @ editor, warned using non-final property in constructor. happens because when create cube, need create square first. when square creating, cube not initialized. (trianglecoords null) therefore, trianglecoords.size throw exception.

how can fix , still use inheritance?

you should pass parameter.

open class square(protected val trianglecoords: floatarray = floatarrayof(         //first triangle         -1.0f, 1.0f, 0.0f, -1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f,         //second triangle         -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f)) {     val coords_per_vertex = 3      private val vertexcount: int = trianglecoords.size / coords_per_vertex      init {         val bb = bytebuffer.allocatedirect(                 trianglecoords.size * 4)         //other code     } }  open class cube(val size: float = 1.0f) : square(floatarrayof(         //front side         // triangle 1         -size, size, size, // top-left         -size, -size, size, // bottom-left         size, -size, size, // bottom-right         // triangle 2         size, -size, size, // bottom-right         size, size, size, // top-right         -size, size, size, // top-left         //and side, left, top, right same way )) { } 

if think ugly, can write factory method , pass array through parameter private constructor.

is supposed work way?

yes