Set Default Start Up Activity Class Java AndroidManifest xml

Example from SDK C:\Program Files\Android\android-sdk-windows\samples\android-10\ApiDemos\src\com\example\android\apis\text\Link.java
Source: //developer.android.com/resources/browser.html?tag=sample
License: //www.apache.org/licenses/LICENSE-2.0
1.) Automatically linkifies using android:autoLink="all"

// res/values/strings.xml
<string name="link_text_auto"><b>text1:</b> This is some text.  In
      this text are some things that are actionable.  For instance,
      you can click on //www.google.com and it will launch the
      web browser.  You can click on google.com too.  And, if you
      click on (415) 555-1212 it should dial the phone.
    </string>
// main.xml
<!-- text1 automatically linkifies things like URLs and phone numbers. -->
  <TextView xmlns:android="//schemas.android.com/apk/res/android"
            android:id="@+id/text1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:autoLink="all"
            android:text="@string/link_text_auto"
            />

2.) Link text by setMovementMethod

// MainActivity.java onCreate
/*Be warned that if you want a TextView with a key listener or movement method not to be focusable, or if you want a TextView without a key listener or movement method to be focusable, you must call setFocusable(boolean) again after calling this to get the focusability back the way you want it. */

TextView t2 = (TextView) findViewById(R.id.text2);
t2.setMovementMethod(LinkMovementMethod.getInstance());

// main.xml
<!-- text2 uses a string resource containing explicit <a> tags to
       specify links. -->
  <TextView xmlns:android="//schemas.android.com/apk/res/android"
            android:id="@+id/text2"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="@string/link_text_manual"
            />

//strings.xml

<string name="link_text_manual"><b>text2:</b> This is some other
      text, with a <a href="//www.google.com">link</a> specified
      via an <a> tag.  Use a \"tel:\" URL
      to <a href="tel:4155551212">dial a phone number</a>.
    </string>

3.) Link as html code using Html.fromHtml()

// MainActivity.java onCreate
        TextView t3 = (TextView) findViewById(R.id.text3);
        t3.setText(
            Html.fromHtml(
                "<b>text3:</b>  Text with a " +
                "<a href=\"//www.google.com\">link</a> " +
                "created in the Java source code using HTML."));
        t3.setMovementMethod(LinkMovementMethod.getInstance());

4.) Link string by SpannableString

        SpannableString ss = new SpannableString(
            "text4: Click here to dial the phone.");

        ss.setSpan(new StyleSpan(Typeface.BOLD), 0, 6,
                   Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        ss.setSpan(new URLSpan("tel:4155551212"), 13, 17,
                   Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);

        TextView t4 = (TextView) findViewById(R.id.text4);
        t4.setText(ss);
        t4.setMovementMethod(LinkMovementMethod.getInstance());

public class Main extends Activity {

private TextView mTextView;
private Activity mAct;
private Intent mIntent;

protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main_layout);
  mTextView = findViewById(R.id.mTextView);
  mAct = getActivity();
  mIntent = getIntent();
 }

}

to:

public class Main extends Fragment{

 private TextView mTextView;
 private FragmentActivity mFrgAct;
 private Intent mIntent;
 private LinearLayout mLinearLayout;
 public View onCreateView(LayoutInflater inflater, ViewGroup container,
          Bundle savedInstanceState) {
          View root = inflater.inflate(R.layout.fragment_main, null);
        return root;
    }

 public void onViewCreated(View view, Bundle savedInstanceState) {
          // you can add listener of elements here
          /*Button mButton = (Button) view.findViewById(R.id.button);
            mButton.setOnClickListener(this); */
          mTextView = view.findViewById(R.id.mTextView);
          mLinearLayout = (LinearLayout)view;
 }
 public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
          mFrgAct = getActivity();
          mIntent = mFrgAct.getIntent(); //  Intent intent = new Intent(getActivity().getIntent());
 }

}

Problem: erroneous entry of id

<RadioButton android:id="idRadio"
                android:text="My radio button"/>

Solution: @+id/

<RadioButton android:id="@+id/idRadio"
                android:text="My radio button"/>

float, double is NaN isNaN() isInfinite() Java Android example.

float f = 0.f;
boolean bIsNaN = Float.isNaN(f);
boolean bIsInfinite = Float.isInfinite(f);

 double d = Math.sqrt(-10);
 boolean b = Double.isNaN(d);

onCreate in MainActivity.java

    @Override
	protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
        setContentView(R.layout.main.xml);
        getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.custom_title);
}

You can add to titlebar different Views by xml file.
custom_title.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="//schemas.android.com/apk/res/android" android:id="@+id/screen"
    android:layout_width="fill_parent" android:layout_height="fill_parent"
    android:orientation="vertical">
    <TextView android:id="@+id/left_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:text="Some text" />

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentRight="true"
       
        android:src="@drawable/ic_launcher" />
    
</RelativeLayout>