Kotlin Null Safety

Kotlin eliminates NullPointerExceptions by enforcing nullable and non-nullable types at compile time. Declare types as nullable (String?) or non-nullable (String), use safe calls (?.), the Elvis operator (??), and smart casts to handle nulls safely without runtime crashes.

Nullable types (String?) can hold null values; non-nullable types (String) cannot. Kotlin enforces this distinction at compile time, preventing null dereferences. Non-nullable types are the default, making null handling explicit and deliberate.

Safe calls (?.) invoke methods only if the object is non-null, returning null otherwise. The Elvis operator (??) provides a default value if the left side is null. Together, they allow concise null handling: val length = name?.length ?: 0 returns the string length or zero if null.

Yes. Refactor functions returning nullable types (String?) to use safe calls, Elvis operators, or smart casts to provide non-null returns with defaults. This preserves code expressiveness while enforcing compile-time null safety and eliminating runtime crashes.

Use non-nullable types by default for variables that always have values. Use nullable types only when a value may legitimately be absent. This explicit distinction makes null handling intentional and reduces accidental dereferencing of null values.

After explicit null checks (if (x != null)), Kotlin smart casts the variable to its non-nullable type automatically within that scope. This eliminates redundant null checks and safely narrows types, preventing null dereference in subsequent code.