LoginActivity.java

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 LoginActivity extends AppCompatActivity {

    //mendeklarasikan variable global dengan tipe akses Private
    private EditText edt_username, edt_password;
    private Button btn_login;
    private String username, password;

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

        //mendeklarasikan id tiap View
        edt_username = (EditText)findViewById(R.id.edt_username);
        edt_password = (EditText)findViewById(R.id.edt_password);
        btn_login = (Button)findViewById(R.id.login);

        //memberikan tombol aksi pada tombol Login
        btn_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                username = edt_username.getText().toString();
                password = edt_password.getText().toString();
                if (username.equals("") || password.equals("")) {
                    Toast.makeText(LoginActivity.this, "Mohon Diisi Dulu", Toast.LENGTH_SHORT).show();
                } else if (username.equals("admin")|| password.equals("admin")) {
                    Intent i = new Intent(LoginActivity.this, MainActivity.class);
                    startActivity(i);
                } else {
                    Toast.makeText(LoginActivity.this, "Username dan Password Salah", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    @Override
    protected void onPause() {
        super.onPause();
        finish();
    }
}