CODEWITHSUNDEEP
javaarraysbufferedwriter
Dinz_N
Dinz_N

Reputation: 23

BufferedWriter not writing the array

I have used a buffered writer to write the contents in an array to a text file

try {
    File file = new File("Details.txt");

    if (!file.exists()) {
        file.createNewFile();
    }

    FileWriter fw = new FileWriter(file.getAbsoluteFile());
    BufferedWriter bw = new BufferedWriter(fw);


    for (String line : customer) {
      bw.write(line); //line 178
      bw.newLine();
    }

    bw.flush();
    bw.close();

    System.out.println("Done");

} catch (IOException e) {
    e.printStackTrace();
}

The customer[] array is as follows:

String customer[] = new String[10];
customer[1]="Anne";
customer[2]="Michelle";

But when I try writing to the file I get the following error:

Exception in thread "main" java.lang.NullPointerException
    at java.io.Writer.write(Unknown Source)
    at HotelFunctions.storeData(CustomerMenu.java:178)
    at MainClass.main(MainClass.java:38)

I found out that the error is caused because customer[0] is null. I want to avoid the null elements and only write the elements that have string content. Is there a way to handle this error?

Upvotes: 0

Views: 365

Answers (2)

John Kugelman
John Kugelman

Reputation: 361655

A couple things. First, array indices start at 0, not 1. You should start at customer[0].

customer[0] = "Anne";
customer[1] = "Michelle";

Second, you could check for null. That's one way.

for (String line: customer) {
    if (line != null) {
        bw.write(line);
        bw.newLine();
    }
}

A better way is to use an ArrayList instead of a raw array. Arrays are fixed size collections. If you want to have a varying number of elements an ArrayList will suit you better. You won't have to guard against null elements. If you add two customers, the list will have two entries, not ten.

List<String> customers = new ArrayList<>();

customers.add("Anne");
customers.add("Michelle");

for (String customer: customers) {
    bw.write(customer);
    bw.newLine();
}

(By the way, I encourage you to use the naming scheme I did above. Regular variables are singular while arrays and lists use the plural: customers is a list, and each element is a customer.)

Upvotes: 2

Pshemo
Pshemo

Reputation: 124235

By default array of objects (like Strings) are filled with null values. So with

String customer[] = new String[10];
customer[1]="Anne";
customer[2]="Michelle";

you are ending with array like [null, "Anne", "Michelle", null, null, ..., null].

Now, code of write method looks like:

public void write(String str) throws IOException {
    write(str, 0, str.length());
}

so when you are passing null (String array is by default filled with nulls) str.length() ends up as null.length() which is invalid since null doesn't have any methods nor fields and NPE is thrown.

If you want to skip null elements you can simply test them with == or != like 

for (String line : customer) {
    if (line != null){
        bw.write(line); 
        bw.newLine();
    }
}

Upvotes: 1

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