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In response to Can Java's NullPointerException be changed to report on which variable was null? thorbjorn-ravn-andersen says:
No, the debug information in the class file does not contain enough information to allow this.
My question is, why not?
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What Causes NullPointerException. The NullPointerException occurs due to a situation in application code where an uninitialized object is attempted to be accessed or modified. Essentially, this means the object reference does not point anywhere and has a null value.
NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.
NullPointerException is thrown when an application attempts to use null in a case where an object is required. These include: Calling the instance method of a null object. Accessing or modifying the field of a null object.
June 01, 2022. CWE-476 Null Pointer Dereference is a programming error that can occur when a program attempts to deference a null pointer. This can happen when the programmer mistakenly assumes that a pointer pointing to NULL is actually pointing to a valid object.
It may not have been a variable at all: it may have been a temporary result, e.g. the result of a method call. By the time the NPE occurs it is just an anonymous stack slot.
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The actual exception points to a particular bytecode instruction, but a language statement may expand into dozens of instructions with a half-dozen different pointers referenced. Additionally, the pointers may have been held in temporary storage (bytecode stack) for the duration of several instructions, so the association with a specific variable name is likely lost.
A fancy debugger could make a fair guess at the variable that was "at fault", but, generally speaking, being pointed to the failing statement should be sufficient (though bearing in mind that the failure may be due to a prior statement whose action was deferred).
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