How to calculate the number of rows (and columns in each row) a text takes in a JTextArea?

Question

After getting interested in the problem presented in the question I tried to approach it few times and failed, and I do not like that :)

I think if the problem was split into sub issues it might help to solve it.

For simplicity lets assume the JTextArea will not change its size, so we do not need to worry about re-evaluation etc. I think the important issues are:

1.How to calculate the number of rows a certain text takes in a JTextArea?

2.What is the relation between the number of columns in a JTextArea and a number of characters it can fit in a row? So we can calculate row length.

Please find included below the sample code presenting the text area to process:

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class TextAreaLines
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                JPanel p = new JPanel();
                JFrame f = new JFrame();
                JTextArea ta = new JTextArea("dadsad sasdasdasdasdasd");
                ta.setWrapStyleWord(true);
                ta.setLineWrap(true);
                ta.setRows(5);
                ta.setColumns(5);
                p.add(ta);
                f.setContentPane(p);
                f.setSize(400, 300);
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.setVisible(true);             
                //BTW the code below prints 1
                System.out.println("ta.getLineCount()="+ta.getLineCount());
            }
        });
    }
}

EDIT1: So I have come up with the following code but the problem is that the output is not what you see, i.e

//for input
//JTextArea ta = new JTextArea("alfred abcdefghijklmnoprstuwvxyz abcdefg");

//we have output    
//s=alfred abcdefghijk
//s=lmnoprstuwvxyz a
//s=bcdefg



        FontMetrics fm = ta.getFontMetrics(ta.getFont());
        String text = ta.getText();
        List<String> texts = new ArrayList<String>();               
        String line = "";
        //no word wrap
        for(int i = 0;i < text.length(); i++)  
        {       
            char c = text.charAt(i);
            if(fm.stringWidth(line +c)  <= ta.getPreferredSize().width)
            {                       
                //System.out.println("in; line+c ="+(line + c));
                line += c;
            }
            else
            {
                texts.add(line);//store the text
                line = ""+c;//empty the line, add the last char
            }
        }
        texts.add(line);                
        for(String s: texts)
            System.out.println("s="+s);

What am I doing wrong, what am I forgetting about? There is no word wrap on the text area.

EDIT2: @trashgod This is the output I am getting. Apparent from this is that we have different default fonts. And the problem in fact might be either font or even system dependent. (PS: I am on Win7).

line: Twas brillig and the slithy tovesD
line: id gyre and gimble in the wabe;
line count: 2
preferred: java.awt.Dimension[width=179,height=48]
bounds1: java.awt.geom.Rectangle2D$Float[x=0.0,y=-12.064453,w=170.0,h=15.09375]
layout1: java.awt.geom.Rectangle2D$Float[x=0.28125,y=-8.59375,w=168.25,h=11.125]
bounds2: java.awt.geom.Rectangle2D$Float[x=0.0,y=-12.064453,w=179.0,h=15.09375]
layout2: java.awt.geom.Rectangle2D$Float[x=0.921875,y=-8.59375,w=177.34375,h=11.125]

Compiling in my head what all of you guys are saying I think that the possibly reliable solution might be to hack the way in which the text area sets its text, and take a full control over it. By running the algorithm (above one, please notice, as suggested by @trashgod the '<' was changed to '<=') in the setText of the area.

What got me to think like this... for example in the sample I have provided if you change text of the textarea to JTextArea ta = new JTextArea("alfred abcdefghijkl\nmnoprstuwvxyz ab\ncdefg"); as it is calculated in my case then it will fit perfectly into the textarea.

EDIT3: This is a kind of solution I quickly hacked, at least now the shown characters and calculated are exactly the same. Can someone else please check it out and let me know, possibly how it works on other machine then Win7? The example below is ready to use you should be able to resize the window and get the printout of lines the same as you see.

import java.awt.BorderLayout;
import java.awt.FontMetrics;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class TextAreaLines
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                JPanel p = new JPanel(new BorderLayout());
                JFrame f = new JFrame();
                final JTextArea ta = new JTextArea("alfred abcdefghijklmnoprstuwvxyz abcdefg");
                ta.addComponentListener(new ComponentAdapter()
                {
                    @Override
                    public void componentResized(ComponentEvent e)
                    {
                        super.componentResized(e);
                        System.out.println("ta componentResized");
                        reformatTextAreaText(ta);
                    }
                });
                //ta.setWrapStyleWord(true);
                ta.setLineWrap(true);
                p.add(ta);
                f.setContentPane(p);
                f.setSize(200, 100);
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.setVisible(true);
            }

            private void reformatTextAreaText(JTextArea ta)
            {
                String text = ta.getText();
                //remove all new line characters since we want to control line braking
                text = text.replaceAll("\n", "");
                FontMetrics fm = ta.getFontMetrics(ta.getFont());
                List<String> texts = new ArrayList<String>();
                String line = "";
                //no word wrap
                for(int i = 0; i < text.length(); i++)
                {
                    char c = text.charAt(i);
                    if(fm.stringWidth(line + c) <= ta.getPreferredSize().width)
                    {
                        //System.out.println("in; line+c ="+(line + c));
                        line += c;
                    }
                    else
                    {
                        texts.add(line);//store the text
                        line = "" + c;//empty the line, add the last char
                    }
                }
                texts.add(line);
                //print out of the lines
                for(String s : texts)
                    System.out.println("s=" + s);
                //build newText for the
                String newText = "";
                for(String s : texts)
                    newText += s + "\n";
                ta.setText(newText);
            }
        });
    }
}

Thanks in advance.

Answer 1

What am I doing wrong, what am I forgetting about?

Nothing, really. I modified your example to use "<=" on the width and to highlight a few features:

1. FontMetrics notes, "the advance of a String is not necessarily the sum of the advances of its characters measured in isolation…"

2. The preferred size of the text component matches the metric bounds pretty well for the widest line. This varies by font due to proportional spacing.

3. TextLayout shows even tighter bounds, but note the "baseline-relative coordinates."

4. The getLineCount() method counts line.separator delimited lines, not wrapped lines.

line: Twas brillig and the slithy toves
line: Did gyre and gimble in the wabe;
line count: 2
preferred: java.awt.Dimension[width=207,height=48]
bounds1: java.awt.geom.Rectangle2D$Float[x=0.0,y=-12.568359,w=205.0,h=15.310547]
layout1: java.awt.geom.Rectangle2D$Float[x=0.0,y=-10.0,w=200.0,h=13.0]
bounds2: java.awt.geom.Rectangle2D$Float[x=0.0,y=-12.568359,w=207.0,h=15.310547]
layout2: java.awt.geom.Rectangle2D$Float[x=1.0,y=-10.0,w=205.0,h=13.0]

import java.awt.Dimension;
import java.awt.FontMetrics;
import java.awt.font.FontRenderContext;
import java.awt.font.TextLayout;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

/** #see http://stackoverflow.com/questions/5979795 */
public class TextAreaLine {

    private static final String text1 =
        "Twas brillig and the slithy toves\n";
    private static final String text2 =
        "Did gyre and gimble in the wabe;";
    private static final JTextArea ta = new JTextArea(text1 + text2);

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

            @Override
            public void run() {
                display();
            }
        });
    }

    static void display() {
        JFrame f = new JFrame();
        ta.setWrapStyleWord(false);
        ta.setLineWrap(false);
        ta.setRows(3);
        f.add(ta);
        f.pack();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
        FontMetrics fm = ta.getFontMetrics(ta.getFont());
        List<String> texts = new ArrayList<String>();
        Dimension d = ta.getPreferredSize();
        String text = ta.getText();
        String line = "";
        for (int i = 0; i < text.length(); i++) {
            char c = text.charAt(i);
            if (c != '\n') {
                if (fm.stringWidth(line + c) <= d.width) {
                    line += c;
                } else {
                    texts.add(line);
                    line = "" + c;
                }
            }
        }
        texts.add(line);
        for (String s : texts) {
            System.out.println("line: " + s);
        }
        System.out.println("line count: " + ta.getLineCount());
        System.out.println("preferred: " + d);
        System.out.println("bounds1: " + fm.getStringBounds(text1, null));
        FontRenderContext frc = new FontRenderContext(null, false, false);
        TextLayout layout = new TextLayout(text1, ta.getFont(), frc);
        System.out.println("layout1: " + layout.getBounds());
        System.out.println("bounds2: " + fm.getStringBounds(text2, null));
        layout = new TextLayout(text2, ta.getFont(), frc);
        System.out.println("layout2: " + layout.getBounds());
    }
}

Answer 2

One thing you can do is use FontMetrics. I wrote some code for splitting JTextAreas up at certain line numbers. The setup code looked like:

Graphics2D g = (Graphics2D) g2;
FontMetrics m = g.getFontMetrics();
int lineHeight = m.getHeight();

This will tell you how tall a line of text is.

Unfortunately, letters have different widths in most fonts. But, you can use the following code to determine the width of a String.

int width = m.getStringBounds("Some String", g).getWidth();

I know this doesn't fully answer your question, but I hope it helps.

If you aren't using word wrap, here is the general algorithm you could use: (in the paint component method)

String text[] = getText().split("\n");
String newText = "";
for (String line: text) {
    newText = line + "| " + line.length() + "\n";
}
setText(newText);

That's the general idea. Not sure how well it would work out. Let me know if you try it.