在JFrame中调整JEditorPane的大小

我正在尝试将JEditorPane添加到JFrame中,并使用pack()调整JFrame的大小。当我启动程序时,默认大小不起任何作用,pack会生成一个高度约为10像素的JEditorPane。如何使JEditorPane以我定义的大小开始?

public class GUIManager extends JFrame {

JButton copyButton = new JButton("Copy");
JButton cutButton = new JButton("Cut");
JButton pasteButton = new JButton("Paste");
JButton selectButton = new JButton("Select All");
JButton clearButton = new JButton("Clear");
JButton searchButton = new JButton("Search");
JButton replaceButton = new JButton("Replace");

JEditorPane editPane;
JScrollPane scrollPane;

JPanel buttons = new JPanel();

public GUIManager(){

    buttons.setLayout(new FlowLayout(FlowLayout.LEFT, 10, 10));

    editPane = new JEditorPane(){

        public boolean getScrollableTrackViewportWidth(){

            return true;

        }

    };
    editPane.setSize(500, 500);
    scrollPane = new JScrollPane(editPane);

    buttons.add(copyButton);
    buttons.add(cutButton);
    buttons.add(pasteButton);
    buttons.add(selectButton);
    buttons.add(clearButton);
    buttons.add(searchButton);
    buttons.add(replaceButton);

    this.add(buttons, BorderLayout.NORTH);
    this.add(scrollPane, BorderLayout.CENTER);
}

}