Null values are one of the most common causes of runtime crashes on the JVM. Java allows null freely, while Kotlin was designed to eliminate NullPointerException at compile time . This topic is extremely important for real-world development, JVM understanding, and interviews . Table of Contents The Null Problem Null Handling in Java Null Safety in Kotlin Safe Calls & Elvis Operator Not-null Assertion (!!) Java and Kotlin Comparison Interview Questions Conclusion 1. The Null Problem A null reference means a variable points to no object. Accessing methods or properties on a null reference causes NullPointerException . 2. Null Handling in Java In Java, any reference type can be null . The compiler does not enforce null checks. Java Example String name = null; System.out.println(name.length()); // NullPointerException To avoid crashes, developers must manually add null checks everywhere. if (name != null) { System.out....