如何找出所选文本的行号？

Question

Assume this very small program:

 1.  package ex1;    
 2.  public interface Resizable {
 3.  void resize();
 4.  }

In my editor, if I select line 2-3 using mouse and say click on a button, I want to highlight these texts and also print, which line numbers were selected exactly for the button.

I can do the highlighting part, but I don't know how to find the line numbers of highlighted texts, As I think, I should use a listener, which will detect any changes in editor.

I think I should use an action listener, which will detect when the button is pressed after selecting text blocks. But how I will know, which lines are selected exactly?

Answer 1

The start and end of the highlight can be taken from the caret position dot and mark respectively. These are offsets in the Document . You must then calculate the number of newlines from the start of the document until the mark/do

    textArea.addCaretListener(new CaretListener() {
        @Override
        public void caretUpdate(CaretEvent e) {
            int startLine = getLine(e.getDot());
            int endLine = getLine(e.getMark());
            ...
        }
    });

private int getLine(int offset) {
    String text = textArea.getDocument().getText(0, offset);
    int linenr = 0;
    int idx = text.indexOf("\n");
    while (idx != -1) {
        linenr++;
        idx = text.indexOf("\n", idx);
    }
    return linenr;
}