import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

        final Button btn =findViewById(R.id.btn_next);
        btn.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v) {
                Toast.makeText(MainActivity.this, "HelloWorl", Toast.LENGTH_SHORT).show();
            }
        });
    }
}