Module java.desktop
Package 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):

The letter 'p' showing its 'reference point' 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

    Fields
    Modifier and Type
    Field
    Description
    protected Font
    font
    The actual Font from which the font metrics are created.

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    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

    Modifier and Type
    Method
    Description
    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 codePoint)
    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.
    FontRenderContext
    getFontRenderContext()
    Gets the FontRenderContext used by this FontMetrics object to measure text.
    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.
    LineMetrics
    getLineMetrics(char[] chars, int beginIndex, int limit, Graphics context)
    Returns the LineMetrics object for the specified character array in the specified Graphics context.
    LineMetrics
    getLineMetrics(String str, int beginIndex, int limit, Graphics context)
    Returns the LineMetrics object for the specified String in the specified Graphics context.
    LineMetrics
    getLineMetrics(String str, Graphics context)
    Returns the LineMetrics object for the specified String in the specified Graphics context.
    LineMetrics
    getLineMetrics(CharacterIterator ci, int beginIndex, int limit, Graphics context)
    Returns the LineMetrics object for the specified CharacterIterator in the specified Graphics context.
    int
    getMaxAdvance()
    Returns an estimate of the maximum advance width of any character in the Font described by this FontMetrics object, with important caveats, enumerated below.
    int
    getMaxAscent()
    Determines the maximum ascent of the Font described by this FontMetrics object.
    Rectangle2D
    getMaxCharBounds(Graphics context)
    Returns the bounds for the character with the maximum bounds in the specified Graphics context.
    int
    getMaxDecent()
    Deprecated.
    As of JDK version 1.1.1, replaced by getMaxDescent().
    int
    getMaxDescent()
    Determines the maximum descent of the Font described by this FontMetrics object.
    Rectangle2D
    getStringBounds(char[] chars, int beginIndex, int limit, Graphics context)
    Returns the bounds of the specified array of characters in the specified Graphics context.
    Rectangle2D
    getStringBounds(String str, int beginIndex, int limit, Graphics context)
    Returns the bounds of the specified String in the specified Graphics context.
    Rectangle2D
    getStringBounds(String str, Graphics context)
    Returns the bounds of the specified String in the specified Graphics context.
    Rectangle2D
    getStringBounds(CharacterIterator ci, int beginIndex, int limit, Graphics context)
    Returns the bounds of the characters indexed in the specified CharacterIterator in the specified Graphics context.
    int[]
    getWidths()
    Gets the advance widths of the first 256 characters in the Font.
    boolean
    hasUniformLineMetrics()
    Checks to see if the Font has uniform line metrics.
    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 declared in class java.lang.Object

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

  • Field Details

    • font

      protected Font font
      The actual Font from which the font metrics are created. This cannot be null.
      See Also:

  • Constructor Details

    • 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:

  • Method Details

    • getFont

      public Font getFont()
      Gets the Font described by this FontMetrics object.
      Returns:
      the Font described by this FontMetrics object.

    • getFontRenderContext

      public FontRenderContext getFontRenderContext()
      Gets the FontRenderContext used by this FontMetrics object to measure text.

      Note that methods in this class which take a Graphics parameter measure text using the FontRenderContext of that Graphics object, and not this FontRenderContext

      Returns:
      the FontRenderContext used by this FontMetrics object.
      Since:
      1.6

    • 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:

    • 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:

    • 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:

    • 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 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:

    • 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:

    • getMaxDecent

      @Deprecated public int getMaxDecent()
      Deprecated.
      As of JDK version 1.1.1, replaced by getMaxDescent().
      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 the Font described by this FontMetrics 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.
      None of these caveats are exposed as they are all implementation details, and there is no practical way to determine when these are in effect. An application which needs a better estimate of the maximum advance, and knows the subset of characters it expects to display can query the advance of each such character to find the widest, however, as discussed above, since the displayed width of a 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 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.

      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 this FontMetrics object.
      See Also:

    • 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.

      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 this FontMetrics object.
      See Also:

    • 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 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.
      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 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.
      Throws:
      NullPointerException - if data is null.
      IndexOutOfBoundsException - if the off and len arguments index characters outside the bounds of the data 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 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.
      Throws:
      NullPointerException - if data is null.
      IndexOutOfBoundsException - if the off and len arguments index bytes outside the bounds of the data array.
      See Also:

    • 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.

    • hasUniformLineMetrics

      public boolean hasUniformLineMetrics()
      Checks to see if the Font has uniform line metrics. A composite font may consist of several different fonts to cover various character sets. In such cases, the FontLineMetrics 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

      public LineMetrics getLineMetrics(String str, Graphics context)
      Returns the LineMetrics object for the specified String in the specified Graphics context.
      Parameters:
      str - the specified String
      context - the specified Graphics context
      Returns:
      a LineMetrics object created with the specified String and Graphics context.
      See Also:

    • getLineMetrics

      public LineMetrics getLineMetrics(String str, int beginIndex, int limit, Graphics context)
      Returns the LineMetrics object for the specified String in the specified Graphics context.
      Parameters:
      str - the specified String
      beginIndex - the initial offset of str
      limit - the end offset of str
      context - the specified Graphics context
      Returns:
      a LineMetrics object created with the specified String and Graphics context.
      See Also:

    • getLineMetrics

      public LineMetrics getLineMetrics(char[] chars, int beginIndex, int limit, Graphics context)
      Returns the LineMetrics object for the specified character array in the specified Graphics context.
      Parameters:
      chars - the specified character array
      beginIndex - the initial offset of chars
      limit - the end offset of chars
      context - the specified Graphics context
      Returns:
      a LineMetrics object created with the specified character array and Graphics context.
      See Also:

    • getLineMetrics

      public LineMetrics getLineMetrics(CharacterIterator ci, int beginIndex, int limit, Graphics context)
      Returns the LineMetrics object for the specified CharacterIterator in the specified Graphics context.
      Parameters:
      ci - the specified CharacterIterator
      beginIndex - the initial offset in ci
      limit - the end index of ci
      context - the specified Graphics context
      Returns:
      a LineMetrics object created with the specified arguments.
      See Also:

    • getStringBounds

      public Rectangle2D getStringBounds(String str, Graphics context)
      Returns the bounds of the specified String in the specified Graphics context. The bounds is used to layout the String.

      Note: The returned bounds is in baseline-relative coordinates (see class notes).

      Parameters:
      str - the specified String
      context - the specified Graphics context
      Returns:
      a Rectangle2D that is the bounding box of the specified String in the specified Graphics context.
      See Also:

    • getStringBounds

      public Rectangle2D getStringBounds(String str, int beginIndex, int limit, Graphics context)
      Returns the bounds of the specified String in the specified Graphics context. The bounds is used to layout the String.

      Note: The returned bounds is in baseline-relative coordinates (see class notes).

      Parameters:
      str - the specified String
      beginIndex - the offset of the beginning of str
      limit - the end offset of str
      context - the specified Graphics context
      Returns:
      a Rectangle2D that is the bounding box of the specified String in the specified Graphics context.
      See Also:

    • getStringBounds

      public Rectangle2D getStringBounds(char[] chars, int beginIndex, int limit, Graphics context)
      Returns the bounds of the specified array of characters in the specified Graphics context. The bounds is used to layout the String created with the specified array of characters, beginIndex and limit.

      Note: The returned bounds is in baseline-relative coordinates (see class notes).

      Parameters:
      chars - an array of characters
      beginIndex - the initial offset of the array of characters
      limit - the end offset of the array of characters
      context - the specified Graphics context
      Returns:
      a Rectangle2D that is the bounding box of the specified character array in the specified Graphics context.
      See Also:

    • getStringBounds

      public Rectangle2D getStringBounds(CharacterIterator ci, int beginIndex, int limit, Graphics context)
      Returns the bounds of the characters indexed in the specified CharacterIterator in the specified Graphics context.

      Note: The returned bounds is in baseline-relative coordinates (see class notes).

      Parameters:
      ci - the specified CharacterIterator
      beginIndex - the initial offset in ci
      limit - the end index of ci
      context - the specified Graphics context
      Returns:
      a Rectangle2D that is the bounding box of the characters indexed in the specified CharacterIterator in the specified Graphics context.
      See Also:

    • getMaxCharBounds

      public Rectangle2D getMaxCharBounds(Graphics context)
      Returns the bounds for the character with the maximum bounds in the specified Graphics context.
      Parameters:
      context - the specified Graphics context
      Returns:
      a Rectangle2D that is the bounding box for the character with the maximum bounds.
      See Also:

    • 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.