This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 8 years ago.
I have faced many time the NullPointerException in android. Some times I understand why the exception is thrown.
My Question is: Android applications are developed in Java and Java does not support pointers, then why is the exception called NullPointerException?
NullPointerException is a situation in code where you try to access/ modify an object which has not been initialized yet. It essentially means that object reference variable is not pointing anywhere and refers to nothing or ‘null’.
A NullPointerException is thrown when you use a null reference. The name is a holdover from an early prototype of Java.
Related
This question already has answers here:
When should we create our own Java exception classes? [closed]
(6 answers)
Closed 2 years ago.
This question may sound stupid, but why do we have to throw several exceptions while we can just throw Throwable or Exception?
As far as I know, this is similar to why, in a try-catch block, programmers like to list out the various exceptions in individual catch clauses rather than just catching Exception overall. This is mostly a readability and documentation best-practice. Anyone else reading your program will know explicitly what errors are being tracked for or thrown. If I'm reading dense code from someone else that is dealing with audio input-output, for example, it is much more informative to me if I know that I can expect a LineUnsupportedException rather than just a generic exception.
This question already has answers here:
What is the difference between a pointer and a reference variable in Java?
(9 answers)
Closed 5 years ago.
Creating a reference in Java is same as the concept of pointer is exactly same, then why it is said that Java does not support pointers?
In C you can manipulate pointers to get somewhere else than the pointer points to. In Java references are atomic and only makes sense to get to an object in memory.
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
NullPointerException Error using linked lists
(2 answers)
Closed 6 years ago.
Let's get to the point. I'm using a LinkedList to store some info about the objects it store. The thing is, I can't set all the attributes of the objects right when I create it, so I need to access them later. In fact, this is the piece of code where I access it.
listaNodos.get(esteNodo(nodoActual)).caminoVuelta.getLast().setFin(currentGrid); listaNodos.get(esteNodo(nodoActual)).caminoVuelta.getLast().setPath(caminoVuelta);
Just as a clarification: caminoVuelta is also a LinkedList.
So, can I modify the atributes of the instances stored in caminoVuelta by simply accessing them with getLast() method from LinkedList and then using the set() methods? Or will this change never happen to the original object?
For some reason, (and it only happens for the first node(Nodo) I create) it returns a NullPointerException.
I hope it's clear enough. Thanks.
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 7 years ago.
req.getParameter("doit").equal("good");
Is it impossible to write this line in the
method? Without it, the program runs correctly. However whenever I write that line, it shows the error messages..
java.lang.NullPointerException at adhoc.FinePrint.doFilter(FinePrint.java:50)
Is there any way that I can check whether "doit" parameter is equal to "good"??
I'd recommend to turn your equals around to
"good".equals(req.getParameter("doit"));
This prevents the NullPointerException when the request parameter "doit" is not set.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Best way to throw exceptions in JNI code?
I see that the System#arraycopy could throw ArrayStoreException or IndexOutOfBoundsException etc.
But I also saw that System#arraycopy is a using a native method, which means C code, right?
So how is it possible that C code could throw any of these java exceptions?
There are no problems in throwing java exception from native code. You can do this easily with code like this one:
jclass cls = env->FindClass("java/lang/ArrayStoreException");
env->ThrowNew(cls, message);