How do you change text to bold in Android?

Programmatically:

You can do programmatically using setTypeface():

textView.setTypeface(null, Typeface.NORMAL);      // for Normal Text
textView.setTypeface(null, Typeface.BOLD);        // for Bold only
textView.setTypeface(null, Typeface.ITALIC);      // for Italic
textView.setTypeface(null, Typeface.BOLD_ITALIC); // for Bold and Italic

XML:

You can set Directly in XML file in <TextView /> like:

android:textStyle="normal"
android:textStyle="normal|bold"
android:textStyle="normal|italic"
android:textStyle="bold"
android:textStyle="bold|italic"

Source:  here

Programmatically:
You can do programmatically using setTypeface() method:



Below is the code for default Typeface 



textView.setTypeface(null, Typeface.NORMAL);      // for Normal Text
textView.setTypeface(null, Typeface.BOLD);        // for Bold only
textView.setTypeface(null, Typeface.ITALIC);      // for Italic
textView.setTypeface(null, Typeface.BOLD_ITALIC); // for Bold and Italic
and if you want to set custom Typeface:



textView.setTypeface(textView.getTypeface(), Typeface.NORMAL);      // for Normal Text
textView.setTypeface(textView.getTypeface(), Typeface.BOLD);        // for Bold only
textView.setTypeface(textView.getTypeface(), Typeface.ITALIC);      // for Italic
textView.setTypeface(textView.getTypeface(), Typeface.BOLD_ITALIC); // for Bold and Italic

XML:
You can set directly in XML file in <TextView /> like this: 



android:textStyle="normal"
android:textStyle="normal|bold"
android:textStyle="normal|italic"
android:textStyle="bold"
android:textStyle="bold|italic"
Or you can set your fav font (from assets). for more info see link