Login Application in Android

FileName: activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.abbu.login_page.MainActivity">

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="187dp"
        android:id="@+id/editTextPass"
        android:hint="password" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textPersonName"
        android:ems="10"
        android:layout_alignBottom="@+id/editTextPass"
        android:layout_alignEnd="@+id/editTextPass"
        android:layout_marginBottom="80dp"
        android:id="@+id/editTextUser"
        android:hint="username" />

    <Button
        android:text="Login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editTextPass"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="72dp"
        android:id="@+id/button" />
</RelativeLayout>

FileName: MainActivity.java

package com.example.abbu.login_page;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    EditText username, password;
    Button login;

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

        username = (EditText) findViewById(R.id.editTextUser);
        password = (EditText) findViewById(R.id.editTextPass);
        login = (Button) findViewById(R.id.button);

        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(username.getText().toString().equals("admin") &&
                        password.getText().toString().equals("admin")){
                    Toast.makeText(MainActivity.this, "Welcome " +
                            username.getText().toString(),
                            Toast.LENGTH_SHORT).show();
                }
                else{
                    Toast.makeText(MainActivity.this, "Invalid Details",
                            Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

Output:
activity_main.xml
After Successful Login
After unsuccessful Login