746: Mainline

When you write strings, the strings are placed on a baseline. Portions of all characters appear above the baseline. Characters such as g and p have descenders that appear below the baseline.

The distance by which a font extends above the baseline is that font's height, whereas the distance by which the font's characters extends below the baseline is the font's descent.

The getFontMetrics method returns an instance of the FontMetrics class. That instance provides height and descent information, via the getHeight and getDescent methods, for the font currently associated with a graphics context. The FontMetrics instance also provides string-width information, via the stringWidth method, for a string argument. The stringWidth method returns the width that the string would occupy if the string were displayed in the font associated with the FontMetrics instance.

You can use information about height and width—using getHeight and stringWidth—to position a string that you draw. In the following example, stringWidth makes it possible to center the string on a baseline located at the middle of the window. The size of the font used varies with the width of the window.

import java.awt.*;
import javax.swing.*;
public class Meter extends JComponent implements MeterInterface {
 String title = "Title to Be Supplied";
 int minValue, maxValue, value;
 public Meter (int x, int y) {
  minValue = x; maxValue = y; value = (y + x) / 2;
 }
 public void setValue(int v) {value = v; repaint();}
 public void setTitle(String t) {title = t; repaint();}
// Define getValuesAtCoordinates as in Segment 745
 public void paint(Graphics g) {
  // Determine window size:
  Dimension d = getSize();                               
  // Prepare font
  int fontSize = d.width / 30;                           
  g.setFont(new Font("Helvetica", Font.BOLD, fontSize)); 
  // Write title:
  FontMetrics f = g.getFontMetrics();                    
  int stringWidth = f.stringWidth(title);                
  int xOffset = (d.width - stringWidth) / 2;             
  int yOffset = d.height / 2;                            
  g.drawString(title, xOffset, yOffset);                 
 } 
 public Dimension getMinimumSize() {return new Dimension(150, 100);}  
 public Dimension getPreferredSize() {return new Dimension(150, 100);}  
}