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):

- `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 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:
  - `Font`
  - Serialized Form

- ## 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:
      - `getFont()`

- ## 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:
      - `Font`

- ## 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:
      - `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()`

  - ### 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:
      - `getMaxDescent()`

  - ### 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:
      - `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.

    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:
      - `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 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:
      - `bytesWidth(byte[], int, int)`
      - `charsWidth(char[], int, int)`
      - `getStringBounds(String, Graphics)`

  - ### 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:
      - `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.
    Throws:
      `NullPointerException` - if `data` is null.
      `IndexOutOfBoundsException` - if the `off` and `len` arguments index bytes outside the bounds of the `data` array.
    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.

  - ### 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:
      - `Font.hasUniformLineMetrics()`

  - ### 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:
      - `Font.getLineMetrics(String, FontRenderContext)`

  - ### 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:
      - `Font.getLineMetrics(String, int, int, FontRenderContext)`

  - ### 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:
      - `Font.getLineMetrics(char[], int, int, FontRenderContext)`

  - ### 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:
      - `Font.getLineMetrics(CharacterIterator, int, int, FontRenderContext)`

  - ### 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:
      - `Font.getStringBounds(String, FontRenderContext)`

  - ### 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:
      - `Font.getStringBounds(String, int, int, FontRenderContext)`

  - ### 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:
      - `Font.getStringBounds(char[], int, int, FontRenderContext)`

  - ### 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:
      - `Font.getStringBounds(CharacterIterator, int, int, FontRenderContext)`

  - ### 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:
      - `Font.getMaxCharBounds(FontRenderContext)`

  - ### 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.