public class MainActivity extends AppCompatActivity {

    EditText username;
    EditText password;
    Button loginbutton;
    DataModel data;

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

        data = new DataModel();

        data.setUsername("Don");
        data.setPassword("Bradman");

        username = (EditText) findViewById(R.id.editusername);
        password = (EditText) findViewById(R.id.editpassword);

        loginbutton = (Button) findViewById(R.id.loginbutton);
        loginbutton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                // Perform action on click
                if (username.getText().toString().equals("Prashant") && password.getText().toString().equals("Joshi")){
                    Toast.makeText(MainActivity.this, "You have successfully logged in", Toast.LENGTH_SHORT).show();
                }
                else {
                    Toast.makeText(MainActivity.this, "Wrong Username or Password", Toast.LENGTH_SHORT).show();
                }
            }
        });

    }
}

public class DataModel {

    String username;
    String password;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="10dp"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="10dp"
    >

    <EditText
        android:id="@+id/editusername"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Username"
        android:inputType="textNoSuggestions"/>

    <EditText
        android:id="@+id/editpassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Password"
        android:inputType="textPassword"/>

    <Button
        android:id="@+id/loginbutton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onLoginClicked"
        android:text="Login Button"/>
</LinearLayout>