尝试在以下位置的空对象引用上调用虚拟方法'boolean java.lang.String.equals（java.lang.Object）'

Question

 This is the errror, tried a few things but still to no avail.

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object referenc e at com.dllibrary.cart.SigninMainActivity$1$1.onDataChange( SigninMainActivity.java:56) at com.google.android.gms.internal.zzegf.zza(Unknown Source) at com.google.android.gms.internal.zzeia.zzbyc(Unknown Source) at com.google.android.gms.internal.zzeig.run(Unknown Source) at android.os.Handler.handleCallback(Handler.java:815) at android.os.Handler.dispatchMessage(Handler.java:104) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5637) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

code for my sign in method

     signin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

           final ProgressDialog mdialog = new       ProgressDialog(SigninMainActivity.this);
            mdialog.setMessage("Please waiting");
            mdialog.show();
            table_user.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    //check if user not exist
                    if (dataSnapshot.child(phone.getText().toString()).exists()) {
                        //Get User Information
                        mdialog.dismiss();

                        User user = dataSnapshot.child(phone.getText().toString()).getValue(User.class);
                       if (user.getPassword().equals(password.getText().toString())) {
                            Intent homeIntent= new Intent(SigninMainActivity.this, home.class);
                            Common.currentUser = user;
                            startActivity(homeIntent);
                            finish();
                        } else {

                            Toast.makeText(SigninMainActivity.this, "Sign in failed", Toast.LENGTH_SHORT).show();


                        }
                    }else{
                        mdialog.dismiss();
                        Toast.makeText(SigninMainActivity.this, "User Does Not exist", Toast.LENGTH_SHORT).show();
                    }
                }

line 56 is at "if(user.getPassword.equals)"

Answer 1

Check the below code I implement with the change I expected.

    signin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

               final ProgressDialog mdialog = new       ProgressDialog(SigninMainActivity.this);
                mdialog.setMessage("Please waiting");
                mdialog.show();
                table_user.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        //check if user not exist
                        if (dataSnapshot.child(phone.getText().toString()).exists()) {
                            //Get User Information
                            mdialog.dismiss();

                            User user = dataSnapshot.child(phone.getText().toString()).getValue(User.class);
//Check the null
                           if (user.getPassword() != null && password.getText() != null && user.getPassword().equals(password.getText().toString())) {
                                Intent homeIntent= new Intent(SigninMainActivity.this, home.class);
                                Common.currentUser = user;
                                startActivity(homeIntent);
                                finish();
                            } else {

                                Toast.makeText(SigninMainActivity.this, "Sign in failed", Toast.LENGTH_SHORT).show();


                            }
                        }else{
                            mdialog.dismiss();
                            Toast.makeText(SigninMainActivity.this, "User Does Not exist", Toast.LENGTH_SHORT).show();
                        }
                    }

Answer 2

The following error:

Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference

Tells you what is all about. It means that in this line of code:

if (user.getPassword().equals(password.getText().toString()))

That exists at line 56 , user.getPassword() returns null .

This is happening because the User object that you are trying to get from the database has the value of null . So to solve this, make sure you get the correct User object. Also, check this object for nullity before actually using it:

if(user != null) {}