[Einsteiger] Button wird nicht angezeigt

ackage com.example.helloandroid;

import android.app.Activity;
import android.os.Bundle;
import android.widget.*;

public class HelloAndroid extends Activity
{
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);


Button button = new Button (this);

button.setWidth(50);
button.setHeight(50);
button.setEnabled (true);
button.setText ("Beenden");
setContentView (button);

TextView tv = new TextView(this);
tv.setText("Hello, Android");
setContentView(tv);


}
}

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