<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
   ...>
   <android.support.design.widget.AppBarLayout
    ...>
       <android.support.design.widget.CollapsingToolbarLayout
        ...>
           <android.support.v7.widget.Toolbar
            .../>
       </android.support.design.widget.CollapsingToolbarLayout>
   </android.support.design.widget.AppBarLayout>

   <include layout="@layout/content_scrolling"/>

    <Button
       android:id="@+id/my_button"
       android:layout_width="match_parent"
       android:layout_height="40dp"
       android:text="my sticky button"
       android:background="#ff0000"
       android:layout_gravity="center_horizontal"
       app:layout_anchor="@id/anchor"
       app:layout_anchorGravity="top"/>

    <android.support.design.widget.FloatingActionButton
    .../>

</android.support.design.widget.CoordinatorLayout>

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="1000dp"
        .../>

    <View
        android:id="@+id/anchor"
        android:layout_height="40dp"
        android:layout_width="match_parent"/>
    <TextView
        android:layout_width="match_parent"
        android:layout_height="200dp"
        .../>
</LinearLayout>

public class StickyBottomBehavior extends CoordinatorLayout.Behavior {
    private Integer mInitialMargin = 100;

@Override
public boolean onStartNestedScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull
        View child, @NonNull View directTargetChild, @NonNull View target, int axes, int type) {
    return (axes == SCROLL_AXIS_VERTICAL);
}

@Override
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull View
        child, @NonNull View target, int dx, int dy, @NonNull int[] consumed, int type) {
    super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);

    updateMargin(coordinatorLayout, child);
}

private void updateMargin(CoordinatorLayout coordinatorLayout, View child) {

    int coordBottom = coordinatorLayout.getBottom();

    //Get anchored View to know its position
    int id = ((CoordinatorLayout.LayoutParams) child.getLayoutParams()).getAnchorId();
    View anchor = coordinatorLayout.findViewById(id);
    int[] anchorLocation = new int[2];
    anchor.getLocationInWindow(anchorLocation);

    int diff = Math.max(coordBottom - anchorLocation[1], 0);

    //add margins according to how close the child is from the bottom
    ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) child.getLayoutParams();
        layoutParams.leftMargin = Math.min(diff/2, mInitialMargin);
        layoutParams.rightMargin = Math.min(diff/2, mInitialMargin);
        child.setLayoutParams(layoutParams);
}