How Java Swing keeps the vertical scroll bar at the bottom

How Java Swing keeps the vertical scroll bar at the bottom
See picture to speak:

The middle Arrow refers to a Jtextpane
Jtextpane was wrapped in JScrollPane.

//Execution results display window Resulttextpane = new Assistpopuptextpane ()  Resulttextpane.setcontenttype  ( "text/html;        Charset=utf-8 ") ;         Resulttextpane.seteditable  (false)  Defaultcaret caret = (Defaultcaret) resulttextpane.getcaret  ()  Caret.setupdatepolicy  (Defaultcaret _update) ;  Scrollpane.setviewportview  (resulttextpane)  

When a push message is received, the content in the Jtextpane dynamically increases to a certain extent, resulting in a vertical scrollbar, so how do you keep the vertical scroll bar at the bottom of Jtextpane?
This way, you can always see the latest push messages.
Realize:
(1) Setting the Jtextpane policy

DefaultCaret caret = (DefaultCaret)resultTextPane.getCaret();        caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

(2) When Jtextpane dynamically adds content

resultTextPane.setSelectionStart(resultTextPane.getText().length());        JScrollBar vertical = scrollPane.getVerticalScrollBar();        vertical.setValue( vertical.getMaximum());

Description
(1) The type of Resulttextpane is Jtextpane;
(2) The difference between Jtextpane and JTextArea:
Jtextpane can set HTML style;
JTextArea cannot be set as HTML style

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Dependent jar Packages:
Dependency Packages

How Java Swing keeps the vertical scroll bar at the bottom