Why does this Android FileOutputStream throw a NullPointerException?

Question

There does not seem to be any Android manifest permission that needs to be set for file io.

public class Device extends Activity {
    private static final Configuration config = new Configuration();
    ...
    private boolean applyMenuChoice(MenuItem item) {
        switch (item.getItemId()) {
        ...
        case R.id.menuSave:
            ...
            configuration.modify(name, to, from, user);
            configuration.write();
            ...

public class Configuration extends Activity {
    private final static String CONFIG = "config.txt";
    private static StringBuilder config = new StringBuilder();
    ...
    public void write() {
        try {
            FileOutputStream fos = openFileOutput(CONFIG, Context.MODE_PRIVATE);
            fos.write(config.toString().getBytes());
            ...

Answer 1

Replacing the illegal instantiation of an activity with correct methods resolved this issue. Thank you very much (again) Falmarri.

Answer 2

Where are you trying to write your file to? If it's on the SD-card of the device, you need to set the WRITE_EXTERNAL_STORAGE-permission in your android-manifest. You may also need to set a path instead of just using a filename.

Answer 3

The exception is thrown in this scenario when this pointer is incorrect. You probably created the activity using its ctor like a regular object and not using start activity of an intent. In this case dont invoke openFileOutput or this.openFileOutput , but you should send the context which you are in as an argument to write() function, and use this context, i.e.:

write(Context context)
{
     context.openFileOutput(...)
     ...