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Copyright © 2006 Sun Microsystems, Inc. All rights reserved.

java.awt
Class FontMetrics

java.lang.Object
  java.awt.FontMetrics

All Implemented Interfaces:

Serializable

public abstract class FontMetrics

extends Object

implements Serializable

The 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):

• getAscent()
• getLeading()
• getMaxAdvance()
• charWidth(char)
• charsWidth(char[], int, int)

Note that the implementations of these methods are inefficient, so they are usually overridden with more efficient toolkit-specific implementations.

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.

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.

Since:

JDK1.0

See Also:

Font, Serialized Form

Field Summary

protected Font

font The actual Font from which the font metrics are created.

Constructor Summary

protected

FontMetrics(Font font) Creates a new FontMetrics object for finding out height and width information about the specified Font and specific character glyphs in that Font.

Method Summary

int	bytesWidth(byte[] data, int off, int len) Returns the total advance width for showing the specified array of bytes in this Font.
int	charsWidth(char[] data, int off, int len) Returns the total advance width for showing the specified array of characters in this Font.
int	charWidth(char ch) Returns the advance width of the specified character in this Font.
int	charWidth(int ch) Returns the advance width of the specified character in this Font.
int	getAscent() Determines the font ascent of the Font described by this FontMetrics object.
int	getDescent() Determines the font descent of the Font described by this FontMetrics object.
Font	getFont() Gets the Font described by this FontMetrics object.
int	getHeight() Gets the standard height of a line of text in this font.
int	getLeading() Determines the standard leading of the Font described by this FontMetrics object.
int	getMaxAdvance() Gets the maximum advance width of any character in this Font.
int	getMaxAscent() Determines the maximum ascent of the Font described by this FontMetrics object.
int	getMaxDescent() Determines the maximum descent of the Font described by this FontMetrics object.
int[]	getWidths() Gets the advance widths of the first 256 characters in the Font.
int	stringWidth(String str) Returns the total advance width for showing the specified String in this Font.
String	toString() Returns a representation of this FontMetrics object's values as a String.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

font

protected Font font

The actual Font from which the font metrics are created. This cannot be null.

See Also:

getFont()

Constructor Detail

FontMetrics

protected FontMetrics(Font font)

Creates a new FontMetrics object for finding out height and width information about the specified Font and specific character glyphs in that Font.

Parameters:

font - the Font

See Also:

Font

Method Detail

getFont

public Font getFont()

Gets the Font described by this FontMetrics object.

Returns:

the Font described by this FontMetrics object.

getLeading

public int getLeading()

Determines the standard leading of the Font described by this FontMetrics 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:

getHeight(), getAscent(), getDescent()

getAscent

public int getAscent()

Determines the font ascent of the Font described by this FontMetrics object. The font ascent is the distance from the font's baseline to the top of most alphanumeric characters. Some characters in the Font might extend above the font ascent line.

Returns:

the font ascent of the Font.

See Also:

getMaxAscent()

getDescent

public int getDescent()

Determines the font descent of the Font described by this FontMetrics object. The font descent is the distance from the font's baseline to the bottom of most alphanumeric characters with descenders. Some characters in the Font might extend below the font descent line.

Returns:

the font descent of the Font.

See Also:

getMaxDescent()

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:

getLeading(), getAscent(), getDescent()

getMaxAscent

public int getMaxAscent()

Determines the maximum ascent of the Font described by this FontMetrics 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:

getAscent()

getMaxDescent

public int getMaxDescent()

Determines the maximum descent of the Font described by this FontMetrics 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:

getDescent()

getMaxAdvance

public int getMaxAdvance()

Gets the maximum advance width of any character in this Font. The advance is the distance from the leftmost point to the rightmost point on the string's baseline. The advance of a String is not necessarily the sum of the advances of its characters.

Returns:

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 ch)

Returns the advance width of the specified character in this Font. The advance is the distance from the leftmost point to the rightmost point on the character's baseline. Note that the advance of a String is not necessarily the sum of the advances of its characters.

Parameters:

ch - the character to be measured

Returns:

the advance width of the specified char in the Font described by this FontMetrics object.

See Also:

charsWidth(char[], int, int), stringWidth(String)

charWidth

public int charWidth(char ch)

Returns the advance width of the specified character in this Font. The advance is the distance from the leftmost point to the rightmost point on the character's baseline. Note that the advance of a String is not necessarily the sum of the advances of its characters.

Parameters:

ch - the character to be measured

Returns:

the advance width of the specified char in the Font described by this FontMetrics object.

See Also:

charsWidth(char[], int, int), stringWidth(String)

stringWidth

public int stringWidth(String str)

Returns the total advance width for showing the specified String in this Font. The advance is the distance from the leftmost point to the rightmost point on the string's baseline.

Note that the total advance width returned from this method does not take into account the rendering context. Therefore, the anti-aliasing and fractional metrics hints can affect the value of the advance. The advance of a String is not necessarily the sum of the advances of its characters.

Parameters:

str - the String to be measured

Returns:

the advance width of the specified String in the Font described by this FontMetrics.

See Also:

bytesWidth(byte[], int, int), charsWidth(char[], int, int)

charsWidth

public int charsWidth(char[] data,
                      int off,
                      int len)

Returns the total advance width for showing the specified array of characters in this Font. The advance is the distance from the leftmost point to the rightmost point on the string's baseline. The advance of a String is not necessarily the sum of the advances of its characters. This is equivalent to measuring a String of the characters in the specified range.

Parameters:

data - the array of characters to be measured

off - the start offset of the characters in the array

len - 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 this FontMetrics object.

See Also:

charWidth(int), charWidth(char), bytesWidth(byte[], int, int), stringWidth(String)

bytesWidth

public int bytesWidth(byte[] data,
                      int off,
                      int len)

Returns the total advance width for showing the specified array of bytes in this Font. The advance is the distance from the leftmost point to the rightmost point on the string's baseline. The advance of a String is not necessarily the sum of the advances of its characters. This is equivalent to measuring a String of the characters in the specified range.

Parameters:

data - the array of bytes to be measured

off - the start offset of the bytes in the array

len - the number of bytes to be measured from the array

Returns:

the advance width of the subarray of the specified byte array in the Font described by this FontMetrics object.

See Also:

charsWidth(char[], int, int), stringWidth(String)

getWidths

public int[] getWidths()

Gets the advance widths of the first 256 characters in the Font. The advance is the distance from the leftmost point to the rightmost point on the character's baseline. Note that the advance of a String 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 this FontMetrics object.

toString

public String toString()

Returns a representation of this FontMetrics object's values as a String.

Overrides:

toString in class Object

Returns:

a String representation of this FontMetrics object.

Since:

JDK1.0.