Inconsistent null pointer exceptions

Question

I am trying to read a .json file from the devices external directory.

I have a class called ExternalFile which is used to read in a file and return the contents as a string.

Here is the class:

public class ExternalFile
{
final String EXTERNAL_STORAGE = Evironment.getExternalStorageDirectory().toString();
final String FIRSTDROID_DIRECTORY = EXTERNAL_STORAGE + "/firstdroid/";
final String SALES_DIRECTORY = FIRSTDROID_DIRECTORY + "sales/";
final String REFERENCE_DIRECTORY = FIRSTDROID_DIRECTORY + "reference/";

public String readFile(String direcectory, String fileName)
{
    BufferedReader br;
    StringBuilder sBuffer;
    File JSON;
    String line;
    String retVal = null;

    try
    {
        sBuffer = new StringBuilder();
        JSON = new File(direcectory, fileName);

        br = new BufferedReader(new FileReader(JSON));
        while ((line = br.readLine()) != null)
        {
            sBuffer.append(line);
            sBuffer.append('\n');
        }

        retVal = sBuffer.toString();

        Log.d("File Results: ", retVal);
    }
    catch (Exception e)
    {
        Log.e("readJSON", e.getMessage());
    }

    return retVal;
}

}

When i use this class to read a "login.json" file, it works fine. However when I use the class to read a "contacts.json" file, eclipse warns: "Null pointer access: The variable readJSON can only be null at this location".

    private void getContactNames()
{
    // File jsonCustomers;
    // BufferedReader br= null;
    // StringBuilder sb = null;
    // String line;
    String result;

    ExternalFile readJSON = null;

    try
    {
            result = readJSON.readFile(REFERENCE_DIRECTORY, "contacts.json");

        // pass through the json string
        readNames(result, "contact");
    }
    catch (Exception e)
    {
        messageBox("getCustomerNames", e.toString());
    }
}

the only difference is that I pass in "contacts.json" instead of "login.json"

sanbhat · Accepted Answer · 2013-08-01 08:22:24Z

5

Eclipse warns if you are using a variable without intializing it. In your code, you have readJSON declared but initialized to null. Right after that its been used inside the try block which will definitely cause NPE

ExternalFile readJSON = null; //--> you have not intialized readJSON 
try
{
     result = readJSON.readFile(REFERENCE_DIRECTORY, "contacts.json");
              ^^^^^^^^
              null access here

answered Aug 1, 2013 at 8:22

sanbhat

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