코드로 숨기기

// 액션바 제거하기
ActionBar actionBar = getSupportActionBar();
if (actionBar != null) {
	actionBar.hide();
}

res/values/themes/themes.xml

<style name="Theme.MyApplication" parent="Theme.AppCompat.Light.NoActionBar">

app bar에 대할 정의를 바꾸기

app bar 색상 변경

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Base application theme. -->
    <style name="Theme.MyApplication" parent="Theme.AppCompat.Light">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/purple_500</item>
        <item name="colorPrimaryVariant">@color/purple_700</item>
        <item name="colorOnPrimary">@color/white</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/teal_200</item>
        <item name="colorSecondaryVariant">@color/teal_700</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor">?attr/colorPrimaryVariant</item>
        <!-- Customize your theme here. -->
    </style>
</resources>

위와 같은 themes.xml 파일에서 android:statusBarColor 속성의 값을 변경하면 된다.