Create Android UI using Java Programming

public class LayoutsActivity extends Activity {
  
    LinearLayout linear;
  
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
      
        LinearLayout linear = new LinearLayout(this);
        Button btn = new Button(this);
        btn.setLayoutParams(new LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,ViewGroup.LayoutParams.WRAP_CONTENT));
        btn.setText("Helllo world");
        linear.addView(btn);
       setContentView(linear);