使用同一类的数据类型的受保护方法时出错

Question

I'm new to Java and I've been trying to create a text program. I've been trying to use a protected method .getRowHeight() from the JTextArea class and call it on an JTextArea object (like in the code below) but I'm getting an error saying "getRowHeight has protected access in javax.swing.JTextArea".

I read online that you can only use protected methods in classes that inherit from the class. But I'm trying to use it on a variable that is from that class, so I thought it would work? Is there a way of making this work without having to inherit from the JTextArea class, because I only really need to use this method once?

Here's a snippet of the code pertaining to userText:

    public class Client extends JFrame {

        private JTextArea userText;

        public Client() {
            userText = new JTextArea(); //2, 2
            userText.setLineWrap(true);     // turns on line wrapping
            userText.setWrapStyleWord(true);
            add(userText, BorderLayout.SOUTH);
            System.out.println(userText.getRowHeight());
        }
    }

Answer 1

You can only call getRowHeight() from a class that belongs to javax.swing package or extends JTextArea .

However, looking at the code of JTextArea , it looks like you can use this method, which is public :

public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
    switch (orientation) {
    case SwingConstants.VERTICAL:
        return getRowHeight(); // this is what you need
    case SwingConstants.HORIZONTAL:
        return getColumnWidth();
    default:
        throw new IllegalArgumentException("Invalid orientation: " + orientation);
    }
}

So, userText.getScrollableUnitIncrement(null,SwingConstants.VERTICAL,0) should return the same output as userText.getRowHeight() .

And in your code :

    public Client() {
        userText = new JTextArea(); //2, 2
        userText.setLineWrap(true);     // turns on line wrapping
        userText.setWrapStyleWord(true);
        add(userText, BorderLayout.SOUTH);
        System.out.println(userText.getScrollableUnitIncrement(null,SwingConstants.VERTICAL,0));
    }