Your oncreate should be like this 
@Override
protected void onCreate(Bundle savedInstanceState) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
        Window w = getWindow();
        w.addFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
        w.addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION);
    }
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}
The Layout File should be like this. 
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#fff"
    tools:context="sslwireless.com.testfullscreen.MainActivity">
    <!--RePresent Toolbar-->
    <LinearLayout
        android:orientation="horizontal"
        android:background="@drawable/gradient"
        android:layout_width="match_parent"
        android:layout_height="100dp">
        <ImageView
            android:layout_gravity="center_vertical"
            android:src="@drawable/ic_arrow_back_white_24dp"
            android:layout_marginLeft="10dp"
            android:layout_width="35dp"
            android:layout_height="35dp" />
        <TextView
            android:layout_gravity="center_vertical"
            android:textSize="25sp"
            android:gravity="center_horizontal"
            android:textColor="#fff"
            android:text="Test Title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </LinearLayout>
</RelativeLayout>
And the gradient file looks like this . 
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient android:angle="135" android:startColor="#f56f2c" android:endColor="#fa9f46"/>
</shape>
The ui will be look like this . 
