why does the toCharArray throw nullpointer?
Code:String allTxt;
allTxt = br.readLine();
char[] araFull = allTxt.toCharArray();
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why does the toCharArray throw nullpointer?
Code:String allTxt;
allTxt = br.readLine();
char[] araFull = allTxt.toCharArray();
Because allTxt is null. Presumably because readline() is returning null.
Always read the API docs so you know what a method does and what values it can return. I'm guessing br is a BufferredReader in which case the API docs say "Returns: A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached"
If there is a chance that you might get null pointer then please use use try catch block , in this case it is a null pointer exception.
Generally speaking you should not catch NullPointerException as they are normally thrown because of a coding error ie you are trying to use a reference which you believe is valid but it isn't.Quote:
If there is a chance that you might get null pointer then please use use try catch block , in this case it is a null pointer exception.
If a variable may be null (eg because, as in this case, the method can return null) you should explicitly test for it not being null before you attempt to use it.
I was going to say that exact thing keang +D. Just because, the board instructions call for me to do so.
my solution:
Code:public static void readOutput() throws IOException{
String allTxt;
int cap;
int read;
try
(BufferedReader br = new BufferedReader(new FileReader(file))) {
allTxt = br.readLine();
cap = allTxt.length();
if(allTxt != null) {
CharArrayWriter caw = new CharArrayWriter(cap);
caw.write(allTxt, 0, cap);
char[] araFull = caw.toCharArray();
// code continues
Do you really think you've solved the problem with this code?Code:allTxt = br.readLine();
cap = allTxt.length();
if(allTxt != null) {...
What's going to happen when the second line runs if allTxt is null?
I am missunderstanding unless that if statment returns true it won't run at all?
But that line of code is before the if statement :rolleyes:
Those variables are not instantiated yet. They are able to be assinged null?
Is a null string anyway isn't it? Because, it has no instantiated value/variable?Code:String s;
:cry: No I mean the line:Quote:
Those variables are not instantiated yet.
It's before the if statement that checks alltxt is not null.Code:cap = allTxt.length();
Excuse my ignorence if I'm wrong but, I thought that 'cap' was considedered null untill assinged to a variable. Sense I am assigning it to a possible null if it's null the cap vairable will not throw an exception. So in my head it will work like this..
Code:try
(BufferedReader br = new BufferedReader(new FileReader(file))) {
allTxt = br.readLine();
cap = allTxt.length(); // at this point both allTxt variable and, cap are considered either
// null or, the integer value of length()/readLine()
if(allTxt != null) { // test's to see if allTxt is null and, if it is the below refrences will not be
// executed, causing no null pointer to be thrown.
CharArrayWriter caw = new CharArrayWriter(cap);
caw.write(allTxt, 0, cap);
char[] araFull = caw.toCharArray();
:confused: Why do you think this has anything to do with cap?Quote:
Excuse my ignorence if I'm wrong but, I thought that 'cap' was considedered null untill assinged to a variable. Sense I am assigning it to a possible null if it's null the cap vairable will not throw an exception. So in my head it will work like this..
cap is presumably an int, ie a primitive type, and so you can't assign null to it anyway, but that aside the issue is not with cap it's with allTxt.
Read what you have written as a comment - how can it make any sense to attempt to call a method on allTxt when it might be null. If allTxt is null there is no object to call the method on and so you get a NullPointerException.Quote:
cap = allTxt.length(); // at this point both allTxt variable and, cap are considered either
// null or, the integer value of length()/readLine()
You assign:
followed byCode:allTxt = br.readLine();
without checking if allTxt is null.Code:cap = allTxt.length();
If br.readLine() returns null, allTxt is null.
If allTxt is null, you get a null pointer exception thrown.
It is thrown because you are trying to use a reference (allTxt) which is pointing to nothing (null), not the assignment of cap.
Ah, yes I see where my mistake is. Null can be anything, but nothing can be null..
Wouldn't I want to check if br.readLine() is null?Quote:
Originally Posted by AlexVV
You can't check if br.readLine() is null, you can only check if br is null or if br.readLine() returns null.Quote:
Wouldn't I want to check if br.readLine() is null?
You don't need to check if br is null because you have created a new BufferedReader object and assigned it to br - ie br can't possibly be null.
The value return from br.readLine() may be a String or it maybe null. You assign the returned value to allTxt ie allTxt may reference a String or it may be null so you need to test allTxt to see if it is null or not.
My missunderstading I forgot, null can be anything, but nothing can be null.