How to read a text file in java and assign lines to variables

Question

Here is the code I wrote :

    try {   
        String[] Flight_Inputs = null;
        Scanner in = new Scanner(f); // f = input file
        int counter =0;
        while(in.hasNextLine()) {
            Flight_Inputs[counter++] = in.next();
          //Flight_Inputs = in.nextLine().split("\n"); // Also tried this
        }
        in.close(); 
         for(int i = 0,j=0; i < Flight_Inputs.length; i++){
             Boeing.setDestination_from(Flight_Inputs[j++]);
             Boeing.setDestination_to(Flight_Inputs[j++]);
             Boeing.setName(Flight_Inputs[j++]);
         }

I am getting Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException error I tried also other variations and got an error that I was trying to access index 1 of Flight_Inputs but compiler says it doesnt exist.

What I want to do do is simply get some lines from the text file and assign them to variables of Boieng object... Any help would be appreciated!

Please try and respect Java naming conventions (variable names should begin with a lowercase letter); it makes it easier for people used to Java to give answers! — fge
– fge, Commented Jun 10, 2013 at 17:35

Pshemo · Accepted Answer · 2013-06-10 17:35:01Z

4

You never initialized Flight_Inputs array, that is why you get java.lang.NullPointerException. Anyway in case you don't know how many lines file will contain you should use List instead like ArrayList<String>.

Try maybe this way:

List<String> lines= new ArrayList<String>();
Scanner in = new Scanner(f); // f = input file
while(in.hasNextLine()) {
    lines.add(in.nextLine());
}
in.close();

Now to iterate over this list you can use

for(String line: lines){
    System.out.println(line);
}

answered Jun 10, 2013 at 17:35

Pshemo

125k26 gold badges194 silver badges280 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Anarkie Over a year ago

Thanks a lot man you saved me once again, works, I also guessed about unknown size but I was using ArrayList for almost everything, every Object list ... and wanted to avoid simple string ...thought strings can have unlimited size, because you can concatenate them etc. well I was wrong need more practice! Thanks again!

Anarkie Over a year ago

Although I used ArrayList<String> lines= new ArrayList<String>(); List gave the error : The type List is not generic; it cannot be parameterized with arguments <String>, I would like to know why for self improvement! :)

Pshemo Over a year ago

@Anarkie I suspect that you imported java.awt.List instead java.util.List.

mrcaramori · Accepted Answer · 2013-06-10 17:53:09Z

4

You should change your Flight_Inputs to a dynamic size list, for example:

change:

//as Pshemo pointed out, this is null, 
//and is causing your NullPointerException
String[] Flight_Inputs = null;
...
Flight_Inputs[counter++] = in.nextLine();
...
for(int i = 0,j=0; i < Flight_Inputs.length; i++){

to:

List<String> Flight_Inputs = new ArrayList<String>();
...
Flight_Inputs.add(in.next());
...
for(String filghtInput : Flight_Inputs){

edited Jun 10, 2013 at 17:53

answered Jun 10, 2013 at 17:34

mrcaramori

2,5034 gold badges29 silver badges49 bronze badges

1 Comment

Pshemo Over a year ago

+1 for nice format of the answer. BTW OP should probably use nextLine() instead of next().

assylias · Accepted Answer · 2013-06-10 17:35:31Z

2

Well yes, String[] Flight_Inputs = null; means that... Flight_Inputs is null.

You would need to instantiate it with a non null value, for example:

String[] Flight_Inputs = new String[size];

except that you probably don't know the size beforehand.

A simpler alternative if y ou use Java 7:

List<String> lines = Files.readAllLines(file, charset);

answered Jun 10, 2013 at 17:35

assylias

330k84 gold badges680 silver badges806 bronze badges

Collectives™ on Stack Overflow

How to read a text file in java and assign lines to variables

3 Answers 3

3 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related