JAVA Error: Variable might not have been initialized in Android Studio

I was trying to create a simple registration app in Android Studio using Java Language.

But I am getting this typical errors cannot find symbol and Variable 'email' might not have been initialized at line number 25 which is String email = email.getText().toString(); in MainActivity.java, even though I am sure that I have initialized all of my variables.

Below is my code of MainActivity.java:

public class MainActivity extends AppCompatActivity {

    EditText firstname, lastname, email, password, repassword;
    Button signup, signin;
    DBHelper DB;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        firstname = (EditText) findViewById(R.id.firstname);
        lastname = (EditText) findViewById(R.id.lastname);
        email = (EditText) findViewById(R.id.email);
        password = (EditText) findViewById(R.id.password);
        repassword = (EditText) findViewById(R.id.repassword);
        signup = (Button) findViewById(R.id.btnsignup);
        signin = (Button) findViewById(R.id.btnsignin);
        DB = new DBHelper(this);

        signup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String fname = firstname.getText().toString();
                String lname = lastname.getText().toString();
                String email = email.getText().toString();
                String pass = password.getText().toString();
                String repass = repassword.getText().toString();

                if(email.equals("")||pass.equals("")||repass.equals(""))
                    Toast.makeText(MainActivity.this, "Please enter all the fields", Toast.LENGTH_SHORT).show();
                else{
                    if(pass.equals(repass)){
                        Boolean checkuser = DB.checkEmail(email);
                        if(checkuser==false){
                            Boolean insert = DB.insertData(fname, lname, email, pass);
                            if(insert==true){
                                Toast.makeText(MainActivity.this, "Registered successfully", Toast.LENGTH_SHORT).show();
                                Intent intent = new Intent(getApplicationContext(),HomeActivity.class);
                                startActivity(intent);
                            }else{
                                Toast.makeText(MainActivity.this, "Registration failed", Toast.LENGTH_SHORT).show();
                            }
                        }
                        else{
                            Toast.makeText(MainActivity.this, "User already exists! please sign in", Toast.LENGTH_SHORT).show();
                        }
                    }else{
                        Toast.makeText(MainActivity.this, "Passwords do not match", Toast.LENGTH_SHORT).show();
                    }
                } }
        });
        signin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), LoginActivity.class);
                startActivity(intent);
            }
        });
    }
}

Below is my code for activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/firstname"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="First Name"
        android:layout_marginTop="50dp"/>

    <EditText
        android:id="@+id/lastname"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Last Name"
        android:layout_marginTop="50dp"
        android:layout_below="@id/firstname"/>

    <EditText
        android:id="@+id/email"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Email"
        android:layout_marginTop="50dp"
        android:layout_below="@id/lastname"/>

    <EditText
        android:id="@+id/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Password"
        android:layout_marginTop="50dp"
        android:layout_below="@+id/email"/>

    <EditText
        android:id="@+id/repassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Retype Password"
        android:layout_marginTop="50dp"
        android:layout_below="@+id/password"/>

    <Button
        android:id="@+id/btnsignup"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Register"
        android:layout_marginTop="50dp"
        android:layout_below="@+id/repassword"/>

    <Button
        android:id="@+id/btnsignin"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Existing user! Go to Sign in page"
        android:layout_marginTop="50dp"
        android:layout_below="@+id/btnsignup"/>

</RelativeLayout>

Any help would be appreciated. I have been going through it a lot of time and reviewed all my variables and I think that I have initialized them before using them. I have searched over the internet and viewed many links, but all of those states that variables should be initialized before using them, and I have made it sure thrice that my variables are initialized. I am fed up with this error. Anyone please look into it and help me sort it out. Thanks in advanced.

>Solution :

Try to change the name of the variable to something other than email:

String mail = email.getText().toString();