ToolbarJustifyFullButton Class

protected void Page_Load(object sender, EventArgs e) {
    HtmlEditorToolbar stToolbar1 = HtmlEditorToolbar.CreateStandardToolbar1();
    ToolbarJustifyLeftButton ljButton = new ToolbarJustifyLeftButton();
    ToolbarJustifyRightButton rjButton = new ToolbarJustifyRightButton();
    ToolbarJustifyCenterButton cjButton = new ToolbarJustifyCenterButton();
    ToolbarJustifyFullButton fjButton = new ToolbarJustifyFullButton();
    stToolbar1.Items.Add(ljButton);
    stToolbar1.Items.Add(rjButton);
    stToolbar1.Items.Add(cjButton);
    stToolbar1.Items.Add(fjButton);
    ASPxHtmlEditor1.Toolbars.Add(stToolbar1);
}

<dx:ASPxHtmlEditor ID="ASPxHtmlEditor1" runat="server">
    <Toolbars>
        <dx:HtmlEditorToolbar Name="StandardToolbar1">
            <Items>
                <dx:ToolbarJustifyLeftButton>
                </dx:ToolbarJustifyLeftButton>
                <dx:ToolbarJustifyCenterButton>
                </dx:ToolbarJustifyCenterButton>
                <dx:ToolbarJustifyRightButton>
                </dx:ToolbarJustifyRightButton>
                <dx:ToolbarJustifyFullButton>
                </dx:ToolbarJustifyFullButton>
            </Items>
        </dx:HtmlEditorToolbar>
    </Toolbars>
</dx:ASPxHtmlEditor>