- All Implemented Interfaces:
Serializable
FontMetrics
class defines a font metrics object, which
encapsulates information about the rendering of a particular font on a
particular screen.
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 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):
Note that the implementations of these methods are inefficient, so they are usually overridden with more efficient toolkit-specific implementations.
When an application asks 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.
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
character array. The advance of a String
is the
distance along the baseline of the String
. This
distance is the width that should be used for centering or
right-aligning the String
.
Note that the advance of a String
is not necessarily
the sum of the advances of its characters measured in isolation
because the width of a character can vary depending on its context.
For example, in Arabic text, the shape of a character can change
in order to connect to other characters. Also, in some scripts,
certain character sequences can be represented by a single shape,
called a ligature. Measuring characters individually does
not account for these transformations.
Font metrics are baseline-relative, meaning that they are
generally independent of the rotation applied to the font (modulo
possible grid hinting effects). See Font
.
- Since:
- 1.0
- See Also:
-
Field Summary
-
Constructor Summary
ModifierConstructorDescriptionprotected
FontMetrics
(Font font) Creates a newFontMetrics
object for finding out height and width information about the specifiedFont
and specific character glyphs in thatFont
. -
Method Summary
Modifier and TypeMethodDescriptionint
bytesWidth
(byte[] data, int off, int len) Returns the total advance width for showing the specified array of bytes in thisFont
.int
charsWidth
(char[] data, int off, int len) Returns the total advance width for showing the specified array of characters in thisFont
.int
charWidth
(char ch) Returns the advance width of the specified character in thisFont
.int
charWidth
(int codePoint) Returns the advance width of the specified character in thisFont
.int
Determines the font ascent of theFont
described by thisFontMetrics
object.int
Determines the font descent of theFont
described by thisFontMetrics
object.getFont()
Gets theFont
described by thisFontMetrics
object.Gets theFontRenderContext
used by thisFontMetrics
object to measure text.int
Gets the standard height of a line of text in this font.int
Determines the standard leading of theFont
described by thisFontMetrics
object.getLineMetrics
(char[] chars, int beginIndex, int limit, Graphics context) Returns theLineMetrics
object for the specified character array in the specifiedGraphics
context.getLineMetrics
(String str, int beginIndex, int limit, Graphics context) getLineMetrics
(String str, Graphics context) getLineMetrics
(CharacterIterator ci, int beginIndex, int limit, Graphics context) Returns theLineMetrics
object for the specifiedCharacterIterator
in the specifiedGraphics
context.int
Returns an estimate of the maximum advance width of any character in theFont
described by thisFontMetrics
object, with important caveats, enumerated below.int
Determines the maximum ascent of theFont
described by thisFontMetrics
object.getMaxCharBounds
(Graphics context) Returns the bounds for the character with the maximum bounds in the specifiedGraphics
context.int
Deprecated.int
Determines the maximum descent of theFont
described by thisFontMetrics
object.getStringBounds
(char[] chars, int beginIndex, int limit, Graphics context) Returns the bounds of the specified array of characters in the specifiedGraphics
context.getStringBounds
(String str, int beginIndex, int limit, Graphics context) Returns the bounds of the specifiedString
in the specifiedGraphics
context.getStringBounds
(String str, Graphics context) Returns the bounds of the specifiedString
in the specifiedGraphics
context.getStringBounds
(CharacterIterator ci, int beginIndex, int limit, Graphics context) Returns the bounds of the characters indexed in the specifiedCharacterIterator
in the specifiedGraphics
context.int[]
Gets the advance widths of the first 256 characters in theFont
.boolean
Checks to see if theFont
has uniform line metrics.int
stringWidth
(String str) Returns the total advance width for showing the specifiedString
in thisFont
.toString()
Returns a representation of thisFontMetrics
object's values as aString
.
-
Field Details
-
font
-
-
Constructor Details
-
FontMetrics
Creates a newFontMetrics
object for finding out height and width information about the specifiedFont
and specific character glyphs in thatFont
.- Parameters:
font
- theFont
- See Also:
-
-
Method Details
-
getFont
Gets theFont
described by thisFontMetrics
object.- Returns:
- the
Font
described by thisFontMetrics
object.
-
getFontRenderContext
Gets theFontRenderContext
used by thisFontMetrics
object to measure text.Note that methods in this class which take a
Graphics
parameter measure text using theFontRenderContext
of thatGraphics
object, and not thisFontRenderContext
- Returns:
- the
FontRenderContext
used by thisFontMetrics
object. - Since:
- 1.6
-
getLeading
public int getLeading()Determines the standard leading of theFont
described by thisFontMetrics
object. The standard leading, or interline spacing, is the logical amount of space to be reserved between the descent of one line of text and the ascent of the next line. The height metric is calculated to include this extra space.- Returns:
- the standard leading of the
Font
. - See Also:
-
getAscent
public int getAscent()Determines the font ascent of theFont
described by thisFontMetrics
object. The font ascent is the distance from the font's baseline to the top of most alphanumeric characters. Some characters in theFont
might extend above the font ascent line.- Returns:
- the font ascent of the
Font
. - See Also:
-
getDescent
public int getDescent()Determines the font descent of theFont
described by thisFontMetrics
object. The font descent is the distance from the font's baseline to the bottom of most alphanumeric characters with descenders. Some characters in theFont
might extend below the font descent line.- Returns:
- the font descent of the
Font
. - See Also:
-
getHeight
public int getHeight()Gets the standard height of a line of text in this font. This is the distance between the baseline of adjacent lines of text. It is the sum of the leading + ascent + descent. Due to rounding this may not be the same as getAscent() + getDescent() + getLeading(). There is no guarantee that lines of text spaced at this distance are disjoint; such lines may overlap if some characters overshoot either the standard ascent or the standard descent metric.- Returns:
- the standard height of the font.
- See Also:
-
getMaxAscent
public int getMaxAscent()Determines the maximum ascent of theFont
described by thisFontMetrics
object. No character extends further above the font's baseline than this height.- Returns:
- the maximum ascent of any character in the
Font
. - See Also:
-
getMaxDescent
public int getMaxDescent()Determines the maximum descent of theFont
described by thisFontMetrics
object. No character extends further below the font's baseline than this height.- Returns:
- the maximum descent of any character in the
Font
. - See Also:
-
getMaxDecent
Deprecated.As of JDK version 1.1.1, replaced bygetMaxDescent()
.For backward compatibility only.- Returns:
- the maximum descent of any character in the
Font
. - See Also:
-
getMaxAdvance
public int getMaxAdvance()Returns an estimate of the maximum advance width of any character in theFont
described by thisFontMetrics
object, with important caveats, enumerated below.The advance is the distance from the leftmost point used to position the character to the rightmost point along the baseline. This is not the same thing as the visible width of the glyph image representing the character.
The advance of a
String
is not necessarily the sum of the advances of its characters. It may differ substantially if complex text layout is required for proper rendering.Some of the caveats of the reported value include
- The returned value is relying upon information from some underlying system font, and the correctness of that information is outside of AWT's control.
- When specific characters are mapped into glyphs in some rendering context, instructions in the font itself together with the rasterization process may cause some glyph to have a wider advance than reported.
- When a font is requested in some style, eg
Font.BOLD
, for which no exact match is available, then techniques to satisfy the requested rendering may similarly result in glyphs that are wider than the reported maximum. - Depending on the implementation, an AWT logical font or
physical font may need to locate some characters from one or more
"fall back" fonts, when the primary underlying physical font does not
support the character. These fonts may not all be known or considered
in the calculation of the reported maximum advance. It is common
for the design center of such fall back fonts to be for a different
script than the design center of the primary font, so their
advances can be quite different. This can also lead to the
unexpected result that a font such as
Font.MONOSPACED
can render glyphs that are not all the same width.
String
is not necessarily the sum of the advances the value still needs to be used with caution.In summary, this method makes no absolute guarantee, nor can it even make a guarantee to be correct within some margin of error. So it should be used at most only for estimating the total space sufficient to display some number of as yet unknown characters from the font. And that might be either an overestimate, or an underestimate depending on the specific text and rendering context.
- Returns:
- an estimate of the maximum advance width of any character
in the
Font
, or-1
if the maximum advance width is not known.
-
charWidth
public int charWidth(int codePoint) Returns the advance width of the specified character in thisFont
. The advance is the distance from the leftmost point to the rightmost point on the character's baseline. Note that the advance of aString
is not necessarily the sum of the advances of its characters.This method doesn't validate the specified character to be a valid Unicode code point. The caller must validate the character value using
Character.isValidCodePoint
if necessary.- Parameters:
codePoint
- the character (Unicode code point) to be measured- Returns:
- the advance width of the specified character
in the
Font
described by thisFontMetrics
object. - See Also:
-
charWidth
public int charWidth(char ch) Returns the advance width of the specified character in thisFont
. The advance is the distance from the leftmost point to the rightmost point on the character's baseline. Note that the advance of aString
is not necessarily the sum of the advances of its characters.Note: This method cannot handle supplementary characters. To support all Unicode characters, including supplementary characters, use the
charWidth(int)
method.- Parameters:
ch
- the character to be measured- Returns:
- the advance width of the specified character
in the
Font
described by thisFontMetrics
object. - See Also:
-
stringWidth
Returns the total advance width for showing the specifiedString
in thisFont
. The advance is the distance from the leftmost point to the rightmost point on the string's baseline.Note that the advance of a
String
is not necessarily the sum of the advances of its characters.- Parameters:
str
- theString
to be measured- Returns:
- the advance width of the specified
String
in theFont
described by thisFontMetrics
. - Throws:
NullPointerException
- if str is null.- See Also:
-
charsWidth
public int charsWidth(char[] data, int off, int len) Returns the total advance width for showing the specified array of characters in thisFont
. The advance is the distance from the leftmost point to the rightmost point on the string's baseline. The advance of aString
is not necessarily the sum of the advances of its characters. This is equivalent to measuring aString
of the characters in the specified range.- Parameters:
data
- the array of characters to be measuredoff
- the start offset of the characters in the arraylen
- the number of characters to be measured from the array- Returns:
- the advance width of the subarray of the specified
char
array in the font described by thisFontMetrics
object. - Throws:
NullPointerException
- ifdata
is null.IndexOutOfBoundsException
- if theoff
andlen
arguments index characters outside the bounds of thedata
array.- See Also:
-
bytesWidth
public int bytesWidth(byte[] data, int off, int len) Returns the total advance width for showing the specified array of bytes in thisFont
. The advance is the distance from the leftmost point to the rightmost point on the string's baseline. The advance of aString
is not necessarily the sum of the advances of its characters. This is equivalent to measuring aString
of the characters in the specified range.- Parameters:
data
- the array of bytes to be measuredoff
- the start offset of the bytes in the arraylen
- the number of bytes to be measured from the array- Returns:
- the advance width of the subarray of the specified
byte
array in theFont
described by thisFontMetrics
object. - Throws:
NullPointerException
- ifdata
is null.IndexOutOfBoundsException
- if theoff
andlen
arguments index bytes outside the bounds of thedata
array.- See Also:
-
getWidths
public int[] getWidths()Gets the advance widths of the first 256 characters in theFont
. The advance is the distance from the leftmost point to the rightmost point on the character's baseline. Note that the advance of aString
is not necessarily the sum of the advances of its characters.- Returns:
- an array storing the advance widths of the
characters in the
Font
described by thisFontMetrics
object.
-
hasUniformLineMetrics
public boolean hasUniformLineMetrics()Checks to see if theFont
has uniform line metrics. A composite font may consist of several different fonts to cover various character sets. In such cases, theFontLineMetrics
objects are not uniform. Different fonts may have a different ascent, descent, metrics and so on. This information is sometimes necessary for line measuring and line breaking.- Returns:
true
if the font has uniform line metrics;false
otherwise.- See Also:
-
getLineMetrics
- Parameters:
str
- the specifiedString
context
- the specifiedGraphics
context- Returns:
- a
LineMetrics
object created with the specifiedString
andGraphics
context. - See Also:
-
getLineMetrics
- Parameters:
str
- the specifiedString
beginIndex
- the initial offset ofstr
limit
- the end offset ofstr
context
- the specifiedGraphics
context- Returns:
- a
LineMetrics
object created with the specifiedString
andGraphics
context. - See Also:
-
getLineMetrics
Returns theLineMetrics
object for the specified character array in the specifiedGraphics
context.- Parameters:
chars
- the specified character arraybeginIndex
- the initial offset ofchars
limit
- the end offset ofchars
context
- the specifiedGraphics
context- Returns:
- a
LineMetrics
object created with the specified character array andGraphics
context. - See Also:
-
getLineMetrics
public LineMetrics getLineMetrics(CharacterIterator ci, int beginIndex, int limit, Graphics context) Returns theLineMetrics
object for the specifiedCharacterIterator
in the specifiedGraphics
context.- Parameters:
ci
- the specifiedCharacterIterator
beginIndex
- the initial offset inci
limit
- the end index ofci
context
- the specifiedGraphics
context- Returns:
- a
LineMetrics
object created with the specified arguments. - See Also:
-
getStringBounds
Returns the bounds of the specifiedString
in the specifiedGraphics
context. The bounds is used to layout theString
.Note: The returned bounds is in baseline-relative coordinates (see
class notes
).- Parameters:
str
- the specifiedString
context
- the specifiedGraphics
context- Returns:
- a
Rectangle2D
that is the bounding box of the specifiedString
in the specifiedGraphics
context. - See Also:
-
getStringBounds
Returns the bounds of the specifiedString
in the specifiedGraphics
context. The bounds is used to layout theString
.Note: The returned bounds is in baseline-relative coordinates (see
class notes
).- Parameters:
str
- the specifiedString
beginIndex
- the offset of the beginning ofstr
limit
- the end offset ofstr
context
- the specifiedGraphics
context- Returns:
- a
Rectangle2D
that is the bounding box of the specifiedString
in the specifiedGraphics
context. - See Also:
-
getStringBounds
Returns the bounds of the specified array of characters in the specifiedGraphics
context. The bounds is used to layout theString
created with the specified array of characters,beginIndex
andlimit
.Note: The returned bounds is in baseline-relative coordinates (see
class notes
).- Parameters:
chars
- an array of charactersbeginIndex
- the initial offset of the array of characterslimit
- the end offset of the array of characterscontext
- the specifiedGraphics
context- Returns:
- a
Rectangle2D
that is the bounding box of the specified character array in the specifiedGraphics
context. - See Also:
-
getStringBounds
public Rectangle2D getStringBounds(CharacterIterator ci, int beginIndex, int limit, Graphics context) Returns the bounds of the characters indexed in the specifiedCharacterIterator
in the specifiedGraphics
context.Note: The returned bounds is in baseline-relative coordinates (see
class notes
).- Parameters:
ci
- the specifiedCharacterIterator
beginIndex
- the initial offset inci
limit
- the end index ofci
context
- the specifiedGraphics
context- Returns:
- a
Rectangle2D
that is the bounding box of the characters indexed in the specifiedCharacterIterator
in the specifiedGraphics
context. - See Also:
-
getMaxCharBounds
Returns the bounds for the character with the maximum bounds in the specifiedGraphics
context.- Parameters:
context
- the specifiedGraphics
context- Returns:
- a
Rectangle2D
that is the bounding box for the character with the maximum bounds. - See Also:
-
toString
-
getMaxDescent()
.