Android - set TextView TextStyle programmatically?

textview.setTypeface(Typeface.DEFAULT_BOLD);

setTypeface is the Attribute textStyle.

As Shankar V added, to preserve the previously set typeface attributes you can use:

textview.setTypeface(textview.getTypeface(), Typeface.BOLD);

Let's say you have a style called RedHUGEText on your values/styles.xml:

<style name="RedHUGEText" parent="@android:style/Widget.TextView">
    <item name="android:textSize">@dimen/text_size_huge</item>
    <item name="android:textColor">@color/red</item>
    <item name="android:textStyle">bold</item>
</style>

Just create your TextView as usual in the XML layout/your_layout.xml file, let's say:

<TextView android:id="@+id/text_view_title" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content 
    android:text="FOO" />

And in the java code of your Activity you do this:

TextView textViewTitle = (TextView) findViewById(R.id.text_view_title);
textViewTitle.setTextAppearance(this, R.style.RedHUGEText);

It worked for me! And it applied color, size, gravity, etc. I've used it on handsets and tablets with Android API Levels from 8 to 17 with no problems. Note that as of Android 23, that method has been deprecated. The context argument has been dropped, so the last line would need to be:

textViewTitle.setTextAppearance(R.style.RedHUGEText);

To support all API levels use androidX TextViewCompat

TextViewCompat.setTextAppearance(textViewTitle, R.style.RedHUGEText)

Remember... this is useful only if the style of the text really depends on a condition on your Java logic or you are building the UI "on the fly" with code... if it doesn't, it is better to just do:

<TextView android:id="@+id/text_view_title" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content 
    android:text="FOO" 
    style="@style/RedHUGEText" />

You can always have it your way!

Search for setTextAppearance or also setTextTypeface. There is similar question on stackoverflow: How to change a TextView's style at runtime