public class MyActivity extends Activity {
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...

        // Pass in the theme attribute that'll resolve to the
        // desired button style resource. The current theme
        // must have a value set for this attribute.
        Button myButton = new Button(this, null, R.attr.myButtonStyle);
        myButton.setText("Hello world");

        ViewGroup containerView = (ViewGroup) findViewById(R.id.container);
        containerView.addView(myButton);
    }
}