Length of a string (text) in pixels.

Question

I'm trying to locate a String's center on an exact position, drawing it to a JPanel. But since i don't know the exact length of the string, it's not that easy. Can anybody help me out there?

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.font.*;
import java.awt.geom.*;
import javax.swing.*;
public class CenteringStrings
    public static void main(String[] args)
        StringDemoPanel demo = new StringDemoPanel();
        DemoActionPanel action = new DemoActionPanel(demo);
        JFrame f = new JFrame("Centering Strings");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(action, "East");
        f.getContentPane().add(demo);
        f.setSize(500,300);
        f.setLocation(200,200);
        f.setVisible(true);
class StringDemoPanel extends JPanel
    String text;
    Font font;
    final int
        ASCENT   = 0,
        DESCENT  = 1,
        LEADING  = 2,
        BASELINE = 3;
    int index = -1;
    boolean sizeFlag, boundsFlag;
    public StringDemoPanel()
        text = "Centered text";
        font = new Font("lucida sans oblique", Font.PLAIN, 36);
        sizeFlag = false;
        boundsFlag = false;
        setBackground(Color.white);
    public void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setFont(font);
        FontRenderContext frc = g2.getFontRenderContext();
        LineMetrics lm = font.getLineMetrics(text, frc);
        TextLayout tl = new TextLayout(text, font, frc);
        int w = getWidth();
        int h = getHeight();
        float textWidth = (float)font.getStringBounds(text, frc).getWidth();
        float ascent  = lm.getAscent();
        float descent = lm.getDescent();
        float leading = lm.getLeading();
        float height  = lm.getHeight();
        float x = (w - textWidth)/2;
        float y = (h + height)/2 - descent;
        g2.drawString(text, x, y);
        // marker for string origin (x,y) on baseline
        //g2.setPaint(Color.blue);
        //g2.fill(new Ellipse2D.Double(x - 1, y - 1, 2, 2));
        // physical space of text
        Rectangle2D textSize = tl.getBounds();
        textSize.setFrame(x, y - textSize.getHeight(),
                          textSize.getWidth(), textSize.getHeight());
        // string bounds
        Rectangle2D bounds = font.getStringBounds(text, frc);
        bounds.setFrame(x, y - ascent - leading, bounds.getWidth(), bounds.getHeight());
        switch(index)
            case ASCENT:
                Rectangle2D r1 = new Rectangle2D.Double(x, y - ascent, textWidth, ascent);
                g2.setPaint(Color.magenta);
                g2.draw(r1);
                break;
            case DESCENT:
                Rectangle2D r2 = new Rectangle2D.Double(x , y, textWidth, descent);
                g2.setPaint(Color.orange);
                g2.draw(r2);
                break;
            case LEADING:
                Rectangle2D r3 = new Rectangle2D.Double(x, y - ascent - leading,
                                                        textWidth, leading);
                g2.setPaint(Color.yellow);
                g2.draw(r3);
                break;
            case BASELINE:
                Line2D line = new Line2D.Double(x, y, x + textWidth, y);
                g2.setPaint(Color.blue);
                g2.draw(line);
        if(sizeFlag)
            g2.setPaint(Color.green);
            g2.draw(textSize);
            System.out.println("above size = " + (int)textSize.getY() + "\n" +
                               "below size = " +
                               (int)(h - (textSize.getY() + textSize.getHeight())));
        if(boundsFlag)
            g2.setPaint(Color.red);
            g2.draw(bounds);
            System.out.println("above bounds = " + (int)bounds.getY() + "\n" +
                               "below bounds = " +
                               (int)(h - (bounds.getY() + bounds.getHeight())));
    public void setIndex(int i)
        index = i;
        repaint();
    public void setSizeFlag(boolean flag)
        sizeFlag = flag;
        repaint();
    public void setBoundsFlag(boolean flag)
        boundsFlag = flag;
        repaint();
class DemoActionPanel extends JPanel
    StringDemoPanel sdp;
    JRadioButton
        ascentButton, descentButton, leadingButton, baselineButton, clearButton;
    JRadioButton[] buttons;
    JCheckBox
        sizeCheck, boundsCheck;
    JCheckBox[] checks;
    public DemoActionPanel(StringDemoPanel p)
        sdp = p;
        createComponents();
    private void createComponents()
        ascentButton   = new JRadioButton("ascent");
        descentButton  = new JRadioButton("descent");
        leadingButton  = new JRadioButton("leading");
        baselineButton = new JRadioButton("baseline");
        clearButton    = new JRadioButton("clear");
        buttons = new JRadioButton[] {
            ascentButton, descentButton, leadingButton, baselineButton, clearButton
        ButtonGroup group = new ButtonGroup();
        RadioButtonListener buttonListener = new RadioButtonListener();
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weighty = 1.0;
        gbc.insets = new Insets(2,2,2,2);
        gbc.gridwidth = gbc.REMAINDER;
        gbc.anchor = gbc.WEST;
        for(int i = 0; i < buttons.length; i++)
            add(buttons, gbc);
group.add(buttons[i]);
buttons[i].addActionListener(buttonListener);
sizeCheck = new JCheckBox("text size");
boundsCheck = new JCheckBox("bounds");
checks = new JCheckBox[] { sizeCheck, boundsCheck };
CheckBoxListener checkBoxListener = new CheckBoxListener();
for(int i = 0; i < checks.length; i++)
add(checks[i], gbc);
checks[i].addActionListener(checkBoxListener);
private class RadioButtonListener implements ActionListener
public void actionPerformed(ActionEvent e)
JRadioButton button = (JRadioButton)e.getSource();
if(button == clearButton)
sdp.setIndex(-1);
return;
for(int i = 0; i < buttons.length; i++)
if(button == buttons[i])
sdp.setIndex(i);
break;
private class CheckBoxListener implements ActionListener
public void actionPerformed(ActionEvent e)
JCheckBox checkBox = (JCheckBox)e.getSource();
if(checkBox == sizeCheck)
sdp.setSizeFlag(sizeCheck.isSelected());
if(checkBox == boundsCheck)
sdp.setBoundsFlag(boundsCheck.isSelected());