如何在JTextArea中的行之间切换

Question

Am trying to set the goto line number for switching between lines in my swing application. I got the number of lines in the JTextArea instance using getLineCount() but don't know how to switch between lines?

Could any one suggest me?

Answer 1

You can set the caret position with textArea.setCaretPosition . Something like this would work

textArea.setCaretPosition(textArea.getDocument().getDefaultRootElement()
                         .getElement(index).getStartOffset());

In the example below, I just use a JComboBox that I populate with the indexes using the line numbers of the JTextArea . When you select on an number in combo box, the caret will move to that line of the JTextArea .

The program is not a great program though. You would probably want to populate the ComboBoxModel dynamically with the addition and removal of lines. But this should give you the answer you're looking for.

Disclaimer

I haven't added any functionality to bring the scrollpane focus the the current line. You may want to look at @Balder comment below for help with that.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;


public class TestCaret {

    public TestCaret() {
        JTextArea textArea = createTextArea();
        JComboBox cBox = createComboBox(textArea);

        JFrame frame = new JFrame();
        frame.add(new JScrollPane(textArea));
        frame.add(cBox, BorderLayout.SOUTH);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private JComboBox createComboBox(final JTextArea textArea) {
        DefaultComboBoxModel<Integer> model  = new DefaultComboBoxModel<>();
        int lines = textArea.getLineCount();
        for (int i = 0; i < lines; i++) {
            model.addElement(i);
        }
        final JComboBox cBox = new JComboBox(model);
        cBox.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e) {
                int index = (Integer)cBox.getSelectedItem();
                textArea.setCaretPosition(
                        textArea.getDocument().getDefaultRootElement().getElement(index).getStartOffset());
                textArea.requestFocusInWindow();
            }
        });
        return cBox;
    }

    private JTextArea createTextArea() {
        JTextArea textArea = new JTextArea(10, 50);
        textArea.setMargin(new Insets(15, 15, 15, 15));
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);
        String text 
                = "0 Hello World\n" + 
                "1 Hello World\n" + 
                "2 Hello World\n" + 
                "3 Hello World\n" + 
                "4 Hello World\n" + 
                "5 Hello World\n" + 
                "6 Hello World\n" +
                "7 Hello World\n" + 
                "8 Hello World\n" + 
                "9 Hello World\n"; 
        textArea.setText(text);
        return textArea;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable(){
            public void run() {
                new TestCaret();
            }
        });
    }
}

Answer 2

One way would be to set up a while statement in the following manner:

String line = null;
while ((line = text.readLine())!=null && line.getLineNumber() < desiredNumber) {}

At the end, line will refer to the line with the desired line number.