public class MainActivity extends AppCompatActivity {


EditText Username_input, Password_input;
String Username, Password;

//if false then no, if true then yes
boolean Registered;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    final SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);

    Button RegisterButton = (Button) findViewById(R.id.Register_btn);
    Button Loginbutton = (Button) findViewById(R.id.Login_btn);

    // If the user is registered.
    if (Registered == false) {

        Loginbutton.setEnabled(false);
        RegisterButton.setEnabled(true);

        // If the user is registered already.
    } else if (Registered == true) {

        Loginbutton.setEnabled(true);
        RegisterButton.setEnabled(false);
    }

    RegisterButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Username_input = (EditText) findViewById(R.id.Username_input);
            Password_input = (EditText) findViewById(R.id.Password_input);
            Username = (String) Username_input.getText().toString();
            Password = (String) Password_input.getText().toString();

            Registered = true;
            SharedPreferences.Editor editor = sharedPref.edit();
            editor.putBoolean("Registered", Registered);
            editor.putString("Username", Username);
            editor.putString("Password", Password);

            Intent intent = getIntent();
            finish();
            startActivity(intent);

        }
    });
}
}