Null Pointer Exception
See also Null References - The Billion Dollar Mistake by Tony Hoare, Tony Hoare, Null (SQL), Null reference, Null pointer, Nullable type, Null-Safety
TLDR: A null pointer exception occurs when a program attempts to access or manipulate an object reference that is null, meaning it points to no memory location or object. This issue, prominent in languages like Java, C Sharp, and CPP, often results from failing to initialize variables, dereferencing null pointers, or improper handling of object references.
https://en.wikipedia.org/wiki/Null_pointer
In Java, the NullPointerException is a runtime exception introduced in 1995 with the release of the language. It occurs when methods or properties are invoked on null objects. For instance, calling a method on an uninitialized object reference will trigger this exception. Proper use of null checks (`if (object != null)`) or using modern features like the Optional class and null-safe operators in Java 8 and above can mitigate such issues.
https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html
Null pointer exceptions often lead to application crashes and debugging challenges, especially in large codebases. To prevent this, many languages have introduced features to minimize null usage. Kotlin, introduced in 2011, provides null-safety as a core feature, requiring developers to explicitly handle nullable types, significantly reducing the likelihood of null pointer exceptions.
https://kotlinlang.org/docs/null-safety.html
Effective practices for handling null pointer exceptions include avoiding null values where possible, using default initializations, and employing static analysis tools like FindBugs or SonarQube to identify potential null dereferencing in the codebase. These approaches ensure better application stability and align with secure coding standards.
https://findbugs.sourceforge.net/
- Snippet from Wikipedia: Null pointer
In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.
A null pointer should not be confused with an uninitialized pointer: a null pointer is guaranteed to compare unequal to any pointer that points to a valid object. However, in general, most languages do not offer such guarantee for uninitialized pointers. It might compare equal to other, valid pointers; or it might compare equal to null pointers. It might do both at different times; or the comparison might be undefined behaviour. Also, in languages offering such support, the correct use depends on the individual experience of each developer and linter tools. Even when used properly, null pointers are semantically incomplete, since they do not offer the possibility to express the difference between a "Not Applicable" value versus a "Not known" value or versus a "Future" value.
Because a null pointer does not point to a meaningful object, an attempt to access the data stored at that (invalid) memory location may cause a run-time error or immediate program crash. This is the null pointer error. It is one of the most common types of software weaknesses, and Tony Hoare, who introduced the concept, has referred to it as a "billion dollar mistake".