Prueba

import android.os.Bundle; import android.widget.Button; import androidx.appcompat.app.AppCompatActivity; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Button button1 = findViewById(R.id.button1); Button button2 = findViewById(R.id.button2); Button button3 = findViewById(R.id.button3); } }