该函数必须在frame.setVisible(true) 之后使用才有用。
下面是官方帮助
Sets the divider location as a percentage of the JSplitPane's size.
This method is implemented in terms of
setDividerLocation(int). This method immediately changes the
size of the split pane based on its current size.
If the split pane is not correctly realized and on
screen, this method will have no effect (new divider
location will become (current size * proportionalLocation)
which is 0)