What should i learn for selecting element from XML file in java android devlopement.

Answer 1

ID of the element in the xml file.
In the java file, access this element by id.

Answer 2

Xml file:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">

<TextView
android:id="@+id/tvOut"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginBottom="50dp"
android:text="TextView">
</TextView>

</LinearLayout>

Answer 3

Java class file:
public class MainActivity extends Activity {
TextView tvOut;

@Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

tvOut = (TextView) findViewById(R.id.tvOut);
tvOut. setText("New some text");
}
}