public class MainActivity extends AppCompatActivity implements View.OnClickListener {

TextView tvRegisterLink;


DatabaseHelper helper = new DatabaseHelper(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    tvRegisterLink = (TextView) findViewById(R.id.tvRegisterLink);

    tvRegisterLink.setOnClickListener(this);
}

public void onButtonClick(View v)
{
    if(v.getId() == R.id.bLogin)
    {
        EditText a = (EditText) findViewById(R.id.etUsername);
        String str = a.getText().toString();
        EditText b = (EditText) findViewById(R.id.etPassword);
        String pass = b.getText().toString();

        String password = helper.searchPass(str);
        if(pass.equals(password))
        {
            Intent i = new Intent(MainActivity.this, Options.class);
            i.putExtra("Username",str);
            startActivity(i);
        }
        else
        {
            Toast temp = Toast.makeText(MainActivity.this , "Username and Password Dont Match!" , Toast.LENGTH_SHORT);
            temp.show();
        }
    }
}

@Override
public void onClick(View v) {
    switch(v.getId()){
        case R.id.tvRegisterLink:
            startActivity(new Intent(this, register.class));

            break;
    }
}

}

public class register extends AppCompatActivity {

DatabaseHelper helper = new DatabaseHelper(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);
}

public void onbRegisterClick(View v)
{
    if(v.getId() == R.id.bRegister)
    {
        EditText username = (EditText) findViewById(R.id.RegUsername);
        EditText password = (EditText) findViewById(R.id.RegPassword);
        EditText password2 = (EditText) findViewById(R.id.RegPassword2);

        String usernamestr = username.getText().toString();
        String passwordstr = password.getText().toString();
        String password2str = password2.getText().toString();

        if(!passwordstr.equals(password2))
        {
            //pop-up message
            Toast pass = Toast.makeText(register.this , "Passwords Do Not Match!" , Toast.LENGTH_SHORT);
            pass.show();
        }
        else
        {
            //insert the details in the database
            Contact c = new Contact();
            c.setUsername(usernamestr);
            c.setPassword(passwordstr);

            helper.insertContact(c);
        }
    }
}
}

public class Options extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_options);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });


    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}

}

public class Contact {

String username, password;

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

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

public class DatabaseHelper extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "contacts.db";
private static final String TABLE_NAME = "contacts";
private static final String COLUMN_ID = "id";
private static final String COLUMN_USERNAME = "username";
private static final String COLUMN_PASSWORD = "password";
SQLiteDatabase db;
private static final String TABLE_CREATE = "create table contacts (id integer primary key not null , " +
        "username text not null , password text not null);";

public DatabaseHelper(Context context)
{
    super(context , DATABASE_NAME , null , DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(TABLE_CREATE);
    this.db = db;
}

public void insertContact(Contact c)
{
    db = this.getWritableDatabase();
    ContentValues values = new ContentValues();

    String query = "Select * from contacts";
    Cursor cursor = db.rawQuery(query, null);
    int count = cursor.getCount();

    values.put(COLUMN_ID, count);
    values.put(COLUMN_USERNAME, c.getUsername());
    values.put(COLUMN_PASSWORD, c.getPassword());

    db.insert(TABLE_NAME, null, values);
    db.close();
}

public String searchPass(String username)
{
    db = this.getReadableDatabase();
    String query = "select username, password from "+TABLE_NAME;
    Cursor cursor = db.rawQuery(query , null);
    String a, b;
    b = "not found";
    if(cursor.moveToFirst())
    {
        do{
            a = cursor.getString(0);


            if(a.equals(username))
            {
                b = cursor.getString(1);
                break;
            }
        }
        while(cursor.moveToNext());
    }

    return b;
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    String query = "DROP TABLE IF EXISTS"+TABLE_NAME;
    db.execSQL(query);
    this.onCreate(db);
}
}