How to debug "Attempt to invoke virtual method on null object reference"?

Question

Beginning of crash:

01-12 10:37:17.953 6865-6865/c.mycompany.cart E/AndroidRuntime: FATAL EXCEPTION: main
                                                            Process: c.mycompany.cart, PID: 6865
                                                            java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
                                                                at c.mycompany.cart.SignIn$1$1.onDataChange(SignIn.java:63)
                                                                at com.google.android.gms.internal.zzbpx.zza(Unknown Source:13)
                                                                at com.google.android.gms.internal.zzbqx.zzZS(Unknown Source:2)
                                                                at com.google.android.gms.internal.zzbra$1.run(Unknown Source:63)
                                                                at android.os.Handler.handleCallback(Handler.java:789)
                                                                at android.os.Handler.dispatchMessage(Handler.java:98)
                                                                at android.os.Looper.loop(Looper.java:164)
                                                                at android.app.ActivityThread.main(ActivityThread.java:6541)
                                                                at java.lang.reflect.Method.invoke(Native Method)
                                                                at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Here is the logcat.

public void onDataChange(DataSnapshot dataSnapshot) {

                    //Check if user dosen't exist in database
                    if (dataSnapshot.child(edtPhone.getText().toString()).exists()) {
                        //Get user information

                        mDialog.dismiss();

                        User user = dataSnapshot.child(edtPhone.getText().toString()).getValue(User.class);
                        if (user.getpassword().equals(edtPassword.getText().toString())) {

                                Intent homeIntent = new Intent(SignIn.this,Home.class);
                                Common.currentUser=user;
                                startActivity(homeIntent);
                                finish();
                            }
                         else {
                            Toast.makeText(SignIn.this, "Incorrect Password !!!", Toast.LENGTH_SHORT).show();
                        }
                    }
                    else
                    {
                        mDialog.dismiss();
                        Toast.makeText(SignIn.this, "User dosen't exist in Database", Toast.LENGTH_SHORT).show();
                    }

                }

Here is the code of the onDataChange function.

share your code basically, the problem is with onDataChange(SignIn.java:63) line number, try to debug your code as well. — yashkal, Jan 15 '18 at 11:11
try to use if(user.getPassword()!=null && user.getpassword().equals(edtPassword.getText().toString())) — yashkal, Jan 15 '18 at 11:54
Sir, I had just used the code that you provided but the same thing is happening. App is getting closed. — Pushpak Chakraborty, Jan 15 '18 at 12:18
Mention the line number with code on which it is crashing. Earlier it is crashing at line number 63 in Signin — yashkal, Jan 15 '18 at 12:30
Sir, I am encountering a problem. Everytime I am trying to run the emulator, it is waiting forever saying "Waiting for target device to come online." Is there any way to find out the logcat while running the app on android device? — Pushpak Chakraborty, Jan 15 '18 at 12:54

Pulak · Answer 1 · 2018-01-15T12:42:33.000

1

Read this question: What is a NullPointerException, and how do I fix it?

You are using equals() on a String object that has not been initialized yet. Check your code and prevent this from happening by making sure your object is initialized before equals() is called.

Wrap your code around if (stringObject != null) so that your app doesn't crash:

if (user.getpassword() != null) {
    if(user.getpassword().equals(edtPassword.getText().toString())) {
        Intent homeIntent = new Intent(SignIn.this,Home.class);
        Common.currentUser=user;
        startActivity(homeIntent);
        finish();
        }else {
            Toast.makeText(SignIn.this, "Incorrect Password !!!", Toast.LENGTH_SHORT).show();
        }
}else {
    Toast.makeText(SignIn.this, "getpassword returned null", Toast.LENGTH_SHORT).show();
}

edited Jan 15 '18 at 12:42

answered Jan 15 '18 at 11:12

Pulak

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I have tried using if (edtPassword != null) But it has not been resolved. – Pushpak Chakraborty Jan 15 '18 at 11:47
Its seems that you try to use equal on null object of User check if the user is null using debugger – Ahmad Nasser Jan 15 '18 at 12:02
I tried using if(user.getpassword()!=null && user.getpassword().equals(edtPassword.getText().toString())) but the app is still getting closed. – Pushpak Chakraborty Jan 15 '18 at 12:19
Even if the above should work, I say you put the second expression inside the `if(user.getpassword() != null)`. Just a shot in the dark. – Pulak Jan 15 '18 at 12:37
@PushpakChakraborty I've edited the answer, have a look – Pulak Jan 15 '18 at 12:43

How to debug "Attempt to invoke virtual method on null object reference"?

1 Answers1