Java: column number and line number of cursor'

问题:

I want to know the column number and row number where the cursor in JTextArea. ie. in notepad when i m at first line than status bar shows Ln 1, Col 1.

thanks in advance...

回答1:

Here is the code

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

public class caretDemo extends JFrame {
    // Two controls, one is the editor and the other is our little status bar at the bottom.
    // When we update the editor, the change in caret will update the status text field.
    private JTextArea editor;
    private JTextField status;

    // Start of our caretDemo class
    public caretDemo() {
        setTitle("Caret Demo");
        setSize(500,500);

        // Lets create a border layout to make positioning of items easy and quick.
        setLayout(new BorderLayout());
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        editor = new JTextArea();

        // Add a caretListener to the editor. This is an anonymous class because it is inline and has no specific name.
        editor.addCaretListener(new CaretListener() {
            // Each time the caret is moved, it will trigger the listener and its method caretUpdate.
            // It will then pass the event to the update method including the source of the event (which is our textarea control)
            public void caretUpdate(CaretEvent e) {
                JTextArea editArea = (JTextArea)e.getSource();

                // Lets start with some default values for the line and column.
                int linenum = 1;
                int columnnum = 1;

                // We create a try catch to catch any exceptions. We will simply ignore such an error for our demonstration.
                try {
                    // First we find the position of the caret. This is the number of where the caret is in relation to the start of the JTextArea
                    // in the upper left corner. We use this position to find offset values (eg what line we are on for the given position as well as
                    // what position that line starts on.
                    int caretpos = editArea.getCaretPosition();
                    linenum = editArea.getLineOfOffset(caretpos);

                    // We subtract the offset of where our line starts from the overall caret position.
                    // So lets say that we are on line 5 and that line starts at caret position 100, if our caret position is currently 106
                    // we know that we must be on column 6 of line 5.
                    columnnum = caretpos - editArea.getLineStartOffset(linenum);

                    // We have to add one here because line numbers start at 0 for getLineOfOffset and we want it to start at 1 for display.
                    linenum += 1;
                }
                catch(Exception ex) { }

                // Once we know the position of the line and the column, pass it to a helper function for updating the status bar.
                updateStatus(linenum, columnnum);
            }
        });

        // Add the fields to the layout, the editor in the middle and the status at the bottom.
        add(editor, BorderLayout.CENTER);

        status = new JTextField();
        add(status, BorderLayout.SOUTH);

        // Give the status update value
        updateStatus(1,1);
    }

    // This helper function updates the status bar with the line number and column number.
    private void updateStatus(int linenumber, int columnnumber) {
        status.setText("Line: " + linenumber + " Column: " + columnnumber);
    }

    // Entry point to the program. It kicks off by creating an instance of our class and making it visible.
    public static void main(String args[]) {
        caretDemo caretDemoApp = new caretDemo();
        caretDemoApp.setVisible(true);
    }
}

---

Output

回答2:

You need to use Utilities.getRowStart along with the caret position as shown below:

To get the row number:

int caretPos = textArea.getCaretPosition();
int rowNum = (caretPos == 0) ? 1 : 0;
for (int offset = caretPos; offset > 0;) {
    offset = Utilities.getRowStart(textArea, offset) - 1;
    rowNum++;
}
System.out.println("Row: " + rowNum);    

To get the column number:

int offset = Utilities.getRowStart(textArea, caretPos);
int colNum = caretPos - offset + 1;
System.out.println("Col: " + colNum);

回答3:

Have you tried getCaretPosition?

You have to count \n to know which line you have, and you have to count the difference between current caret position and last occurrence of \n character.