Why am I getting NullPointerException? bufferWriter.close()

Question

I am new to this, but I am writing an app and I keep getting this error cause the app to crash on start.

java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference

The code causing it is in the class below, there will be a HERE comment next to the line with the issue.

public class FileOptions extends Activity{

public void createFile(String title, String storeValue){
    BufferedWriter bufferWriter = null;
    try {
        FileOutputStream fileOutputStream = openFileOutput(title, Context.MODE_PRIVATE);
        bufferWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));

        String content = storeValue;

        bufferWriter.write(content);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    catch (IOException e) {  //Cannot be removed
        e.printStackTrace();
    }
    finally {
        try {
       /**HERE*/ bufferWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}
//More unimportant stuff
}

This is the code where I am calling the method from.

public class MainActivity extends ActionBarActivity {
Context context = this;
boolean debug = true;
FileOptions file = new FileOptions();
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Boolean isFirstRun = getSharedPreferences("PREFERENCE", MODE_PRIVATE)
            .getBoolean("isfirstrun", true);

    if(isFirstRun) {
        file.createFile("userInfo", "");
        getSharedPreferences("PREFERENCE", MODE_PRIVATE).edit()
                .putBoolean("isfirstrun", false).commit();
    }

    if(file.readFile("userInfo") != "")
    {
        if(debug){alerter(file.readFile("userInfo"));alerter("true");}
        switchToHome();
    }else{
        if(debug){alerter("false");}
    }
}
}

Here is the stack trace.

08-27 22:44:35.830  13089-13089/? I/libpersona﹕ KNOX_SDCARD checking this for 10247

08-27 22:44:35.830  13089-13089/? I/libpersona﹕ KNOX_SDCARD not a persona

08-27 22:44:35.830  13089-13089/? E/Zygote﹕ MountEmulatedStorage()

08-27 22:44:35.830  13089-13089/? E/Zygote﹕ v2

08-27 22:44:35.830  13089-13089/? I/SELinux﹕ Function: selinux_compare_spd_ram, SPD-policy is existed. and_ver=SEPF_SM-N910V_5.0.1 ver=27

08-27 22:44:35.830  13089-13089/? I/SELinux﹕ Function: selinux_compare_spd_ram , priority [1] , priority version is VE=SEPF_SM-N910V_5.0.1_0027

08-27 22:44:35.830  13089-13089/? E/SELinux﹕ [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL

08-27 22:44:35.830  13089-13089/? I/art﹕ Late-enabling -Xcheck:jni

08-27 22:44:35.870  13089-13089/? D/TimaKeyStoreProvider﹕ TimaSignature is unavailable

08-27 22:44:35.870  13089-13089/? D/ActivityThread﹕ Added TimaKeyStore provider

08-27 22:44:35.920  13089-13089/? D/ResourcesManager﹕ creating new AssetManager 
and set to /data/app/preventioninnovations.preventapp-2/base.apk

08-27 22:44:36.050  13089-13089/? D/AndroidRuntime﹕ Shutting down VM

08-27 22:44:36.050  13089-13089/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: preventioninnovations.preventapp, PID: 13089
    java.lang.RuntimeException: Unable to start activity ComponentInfo{preventioninnovations.preventapp/preventioninnovations.preventapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2712)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2777)
            at android.app.ActivityThread.access$900(ActivityThread.java:179)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:145)
            at android.app.ActivityThread.main(ActivityThread.java:5972)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
            at preventioninnovations.preventapp.FileOptions.createFile(FileOptions.java:37)
            at preventioninnovations.preventapp.MainActivity.onCreate(MainActivity.java:38)
            at android.app.Activity.performCreate(Activity.java:6289)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2777)
            at android.app.ActivityThread.access$900(ActivityThread.java:179)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:145)
            at android.app.ActivityThread.main(ActivityThread.java:5972)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)

Thanks for any help.

possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — njzk2, Aug 28 '15 at 03:12
before calling bufferWriter.close() check whether it is not null. if it is null, you can not call .close() which returns NPE. — Nomesh DeSilva, Aug 28 '15 at 03:12
It may be similar but I feel that with the differences in the code it is OK to ask a new question. — Josh Young, Aug 28 '15 at 03:13
Well the same code works if I don't separate it out into a class, so I guess that is what I am going with. I realize that you can check if it is null but then it will not create the file needed(I think?) — Josh Young, Aug 28 '15 at 04:06

score 5 · Answer 1 · answered Aug 28 '15 at 03:03

This happens when your openFileOutput() method throws an exception.

Since an exception was thrown bufferWriter was not initialized to a valid object.

And the exception caused the execution to skip the rest of try block go to catch block and then finally block.

So, when it reached the finally block, bufferWriter was null.

finally {
        try {
            if (bufferWriter != null)
                bufferWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

To fix, check for null before calling close in bufferWriter.

Or still better use try with resources.

try(BufferedWriter = new BufferedWriter(
                         new OutputStreamWriter(
                             openFileOutput(title, Context.MODE_PRIVATE)))) {}

score 1 · Answer 2 · answered Aug 28 '15 at 03:06

1

finally {
    if(bufferWriter!=null){
        bufferWriter.close();/**HERE*/
    }
}

By the looks your bufferWriter is null. So maybe the file you are giving it is not working? This stop a NPE if bufferwriter is null.

answered Aug 28 '15 at 03:06

Chris

460
8
16

score 1 · Answer 3 · edited May 23 '17 at 12:06

Java 7 gives you a much cleaner interface for try-catch blocks.

You can read more on the alternative methods from this SO answer.

public void createFile(String title, String storeValue){
    try (
        FileOutputStream fileOutputStream = openFileOutput(title, Context.MODE_PRIVATE);
        BufferedWriter bufferWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream))
    ) {
        String content = storeValue;
        bufferWriter.write(content);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

score 0 · Answer 4 · answered Aug 28 '15 at 04:48

Found the issue. I needed to pass the context of the class I was calling from to the method for it to work.

I had:file.createFile("userInfo", ""); and I needed:file.createFile("userInfo", "", this);

then in the method I had:

public void createFile(String title, String storeValue){
    BufferedWriter bufferWriter = null;
    try {
        FileOutputStream fileOutputStream = openFileOutput(title, context.MODE_PRIVATE);
        bufferWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));

Where I needed:

public void createFile(String title, String storeValue, /** ADDED */Context context){
    BufferedWriter bufferWriter = null;
    try {
        FileOutputStream fileOutputStream = /** CHANGE IS HERE */ context.openFileOutput(title, context.MODE_PRIVATE);
        bufferWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));

Why am I getting NullPointerException? bufferWriter.close()

4 Answers4