<activity
        android:name="com.example.LoginMain"
        android:label="@string/app_name"
        android:screenOrientation="portrait"
        android:theme="@style/Theme.AppCompat.Light.NoActionBar.FullScreen"
        android:windowSoftInputMode="stateAlwaysHidden" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

<style name="Theme.AppCompat.Light.NoActionBar.FullScreen" parent="@style/Theme.AppCompat.Light">
    <item name="android:windowNoTitle">true</item>
    <item name="windowActionBar">false</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowContentOverlay">@null</item>
</style>

public class LoginMain extends Activity{

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.login);
}

public class LoginMain extends Activity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.login);
    }

android:theme="@android:style/Theme.Black.NoTitleBar"

<style name="myOwnTheme" parent="@style/Theme.AppCompat.Light">
        <item name="windowNoTitle">true</item>
        <item name="windowActionBar">false</item>
        <item name="android:windowFullscreen">true</item>
        <item name="android:windowContentOverlay">@null</item>
    </style>

android:theme="@style/myOwnTheme"

getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                    WindowManager.LayoutParams.FLAG_FULLSCREEN);

<style name="Theme.AppCompat.Light.NoActionBar"  parent="@style/Theme.AppCompat.Light">
<item name="windowNoTitle">true</item>
<item name="windowActionBar">false</item>
</style>

parent="@style/Theme.AppCompat.Light.NoActionBar"