mirokolodii

@Test
    public void FilterClickShouldChangeRecyclerViewCount() {
        // Get items count before action
        RecyclerView recyclerView = mActivityTestRule.getActivity().findViewById(R.id.recycler_view);
        int countBefore = Objects.requireNonNull(recyclerView.getAdapter()).getItemCount();
        Log.e("count", "Items count before: " + countBefore);

        // Perform action
        ViewInteraction actionMenuItemView = onView(
                allOf(

mirokolodii

String someStr1 = "";   // initialized with empty string
String someStr2;        // by default value of someStr2 is null

mirokolodii

val someStr1: String = ""     // same as in Java, i.e initialized with empty string
val someStr2: String          // warning: no default value assigned. Should be initialized 
                              // with a non-null value before its first use
val someStr3: String = null   // error: can't be null

mirokolodii

val someStr1: String? = null // valid statement, notice a question mark after 'String'
val someStr2: String? // warning: no default value assigned. Should be initialized 
                      // with some (nullable or non-nullable) value before its first use

mirokolodii

Class Test(val someInt: Int)
val test1: Test           // warning: no default value, should be initialized 
                          // with non-null value before first use
val test2: Test = null    // error: non-nullable type can't hold null value
val test3: Test? = null   // valid

mirokolodii

var nullableStr: String? = null
var nonNullStr: String = "a string"
nullableStr = nonNullStr              // valid
nonNullStr = nullableStr              // error, should be checked for nullability first
If (nullableStr != null) {
  nonNullStr = nullableStr            // valid
}

mirokolodii

Integer intObj = null;
int primitiveInt;
primitiveInt = intObj; // NullPointerException during unboxing

mirokolodii

Integer nullInt = null;
if (someInt.equals(23)) { // NullPointerException because of attempt to call
                          // a method on a null
  // Rest of code
} 

mirokolodii

var nonNullInt = 1
val nullInt: Int? = null
// 1. Error
nonNullInt = nullInt // Error: type mismatch
// 2. Valid
if (nullInt != null) {
    /* Here is used a smart cast (one of Kotlin compiler's feature),
       which casts Int? to Int automatically */
    nonNullInt = nullInt 
}

mirokolodii

val nonNullInt = 1
val nullInt: Int? = null
if (nullInt == nonNullInt) {
  println("Both are equal")
} else {
  println("Not equal") // Result is 'Not equal'
}