Problem in Substring

[Ranet Saed]

Hi ,I have a text file and it contains a message ,I want to extract the last four characters in this file and then convert it to integer i did the following:
FileInputStream Received_Message=new FileInputStream ("MyFile.txt");
BufferedReader buff2=new BufferedReader(new InputStreamReader(Received_Message));

System.out.println("Your Received message is as following:");
while((recv_Message=buff2.readLine() )!=null){
System.out.println(recv_Message);
}

four_characters=recv_Message.substring(recv_Message.length() - 4);
Four_characters_Integers = Integer.parseInt(four_characters);
i sure have try and catch and defined all varibles above
but the problem it gives me this message when i use this statement:
four_characters=recv_Message.substring(recv_Message.length() - 4);
the Exception is as following:
java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:373)
at java.lang.Integer.parseInt(Integer.java:454)
at final_append.CopyBytes.main(CopyBytes.java:101)
Exception in thread "main"
how can i solve this??plz any help in

[pascal betz]

hi

first something else...
- use code tags to format code you post!
- try to stick with the coding guidelines from sun (recv_Message -> recvMessage, Four_characters_Integers -> fourCharacterIntegers and so on). this code is hard to read!


the exception does not occur in the line

  four_characters=recv_Message.substring(recv_Message.length() - 4);  

since it is an exception that is thrown by Integer.parseInt()!

but the line you mention is probably the problem: as the exception says you are passing null in the parseInt() call. what is the value of four_characters ? can you show the full code ?

pascal

[Steve Bret]

This should do what you want:

try to follow the rules when naming variables/objects
variables should start with a small characters
So Receive_Message --> receiveMessage
...

  
public static void main(String[] args) {
String recv_Message = null;
try {
FileInputStream Received_Message = new FileInputStream("MyFile.txt");
BufferedReader buff2 = new BufferedReader(new InputStreamReader(Received_Message));
 
System.out.println("Your Received message is as following:");
String four_characters = null;
int Four_characters_Integers;
 
while ((recv_Message = buff2.readLine()) != null) {
System.out.println(recv_Message);
four_characters = recv_Message.substring(recv_Message.length() - 4);
Four_characters_Integers = Integer.parseInt(four_characters);
four_characters = recv_Message.substring(recv_Message.length() - 4);
System.out.println("last four characters are:" + four_characters);
}
} catch (FileNotFoundException e) {
System.out.println("Cannot find file MyFile.txt \n" + e);
} catch (IOException e) {
System.out.println("IOException " + e);
} catch (NumberFormatException e) {
System.out.println("Not a number on the last 4 characters : " + recv_Message + "\n" + e);
}
}
 
  

[Jass Singh]

Wouldn't it be better if you use RandomAccessFile and directly call seek(length()-4) to move to last but 4th postion and read last 4 characters, rather than readnig whole file in a whilr loop.

Regards,
Jass

[Ranet Saed]

I have the same problem it gives me an ecxeption ,I tried your code Steve but i had this statement which you put in the exception:
Not a number on the last 4 characters
but the problem is the recv_message is as following:
Hello Bob, how are you? I am going to go to the movie tonight. I plan to see Gonewith the Wind. I really like Clark Gable. Would you like to go with me? I would really like to have some company. Your friend, Alice5113350515586806264156901277970003516182249744328267808527911381008517422384937086806339111024080220

i got it from appending two files
the last four characters 0220 i got them from representing the length of the message in four characters by this code :

String My_Meesage_Length = "" + len;
//Confirm number of characters in the string.
if((My_Meesage_Length.length() > 4)
|| (My_Meesage_Length.length() <= 0)){
System.out.println("Message length error.");
System.exit(0);
}//end if
//Prepend leading zeros if necessary
if(My_Meesage_Length.length() == 1){
aliceMsgLenAsStr = "000"
+My_Meesage_Length;
}else if(My_Meesage_Length.length() == 2){
My_Meesage_Length= "00" + My_Meesage_Length;
}else if(aliceMsgLenAsStr.length() == 3){
My_Meesage_Length = "0" + My_Meesage_Length;
}else if(My_Meesage_Length.length() == 1){
My_Meesage_Length = "000"
+ My_Meesage_Length;
}
System.out.println(My_Meesage_Length);

so this may makes the problem more clear...
so by this the last four characters are numbers so why it keeps give me the same problem...plz any help

[Garrett Rowe]

If you are using Java 5, you can use a Scanner:

FileInputStream Received_Message=new FileInputStream ("MyFile.txt");
BufferedReader buff2=new BufferedReader(new InputStreamReader(Received_Message));
 
Scanner scan = new Scanner(buff2);
scan.useDelimiter("\\Z"); //read to the end of the file
 
String text = scan.next();
String lastFour = text.substring(text.length() - 4);
 
int myInt;
if (lastFour.matches("\\d{4}")
{
   myInt = Integer.parseInt(lastFour);
}
 
else 
{
   throw new WTFException();
}  

[ May 06, 2006: Message edited by: Garrett Rowe ]

[samir Sadiki]

Hi Ranet,
Take a closer look at what you are doing here:

    
while((recv_Message=buff2.readLine() )!=null){
System.out.println(recv_Message);
}
 
four_characters=recv_Message.substring(recv_Message.length() - 4);

when u leave the loop, recv_Message is null and yet after that u r trying to get the last 4 characters from null!!!
try this instead:

   
String recv_Message;
String line = "";
System.out.println("Your Received message is as follows:");
while((recv_Message=buff2.readLine() )!=null){
line = recv_Message;
System.out.println(line);

}
                String four_characters=line.substring(line.length() - 4);
int four_characters_Integers = Integer.parseInt(four_characters);
System.out.println(four_characters);

[samir Sadiki]

...and u might wanna reconsider ur variable names as well... lol.javascript:%20x()
Good luck

[Ranet Saed]

Hi ....Thanks Samir a lot u really helped me with my problem ...i didnt take care of wut i did before...any way i want to ask about another problem i have in the same Class ...I have to append two strings but each one must be saved in a seperate text file ,so the requiered here is to append two text files ...I did that ,but the problem was that each string was in a separate line i dont know why ...for example if i have two text files file1.txt[Hi Bib how are You]
file2.txt[1243456778889990]
the result for the appending was
Hi Bob how are You
1243456778889990

but sure i need this result:
Hi Bob how are You1243456778889990
my code is as folowing:

/ create writer for file to append to
BufferedWriter out = new BufferedWriter(
new FileWriter("file1.txt", true));
// create reader for file to append from
BufferedReader in = new BufferedReader(new FileReader("file2.txt"));
String str;
while ((str = in.readLine()) != null) {
out.write(str);
}
in.close();
out.close();

so how can modify my code to make the right apending as I need???

[Ranet Saed]

Hi plz i need an argent and good help in the problem of the two files to append