java.lang.Object | +----java.awt.FontMetrics
public abstract class FontMetrics
extends Object
implements Serializable
A font metrics object, which gives information about the rendering of a particular font on a particular screen. Note that the implementations of these methods are inefficient, they are usually overridden with more efficient toolkit-specific implementations.
Note to subclassers: Since many of these methods form closed mutually recursive loops, you must take care that you implement at least one of the methods in each such loop in order to prevent infinite recursion when your subclass is used. In particular, the following is the minimal suggested set of methods to override in order to ensure correctness and prevent infinite recursion (though other subsets are equally feasible):
When an application asks AWT to place a character at the position
(x, y), the character is placed so that its
reference point (shown as the dot in the accompanying image) is
put at that position. The reference point specifies a horizontal
line called the baseline of the character. In normal
printing, the baselines of characters should align.
In addition, every character in a font has an ascent, a descent, and an advance width. The ascent is the amount by which the character ascends above the baseline. The descent is the amount by which the character descends below the baseline. The advance width indicates the position at which AWT should place the next character.
If the current character is placed with its reference point at the position (x, y), and the character's advance width is w, then the following character is placed with its reference point at the position (x + w, y). The advance width is often the same as the width of character's bounding box, but need not be so. In particular, oblique and italic fonts often have characters whose top-right corner extends slightly beyond the advance width.
An array of characters or a string can also have an ascent, a descent, and an advance width. The ascent of the array is the maximum ascent of any character in the array. The descent is the maximum descent of any character in the array. The advance width is the sum of the advance widths of each of the characters in the array.