Module java.desktop
Package javax.swing.text

Class StyleContext

  • All Implemented Interfaces:
    Serializable, AbstractDocument.AttributeContext
    Direct Known Subclasses:
    StyleSheet
    public class StyleContext
extends Object
implements Serializable, AbstractDocument.AttributeContext
    A pool of styles and their associated resources. This class determines the lifetime of a group of resources by being a container that holds caches for various resources such as font and color that get reused by the various style definitions. This can be shared by multiple documents if desired to maximize the sharing of related resources.

    This class also provides efficient support for small sets of attributes and compresses them by sharing across uses and taking advantage of their immutable nature. Since many styles are replicated, the potential for sharing is significant, and copies can be extremely cheap. Larger sets reduce the possibility of sharing, and therefore revert automatically to a less space-efficient implementation.

    Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

    • Field Detail

      • DEFAULT_STYLE

        public static final String DEFAULT_STYLE
        The name given to the default logical style attached to paragraphs.
        See Also:
        Constant Field Values

    • Constructor Detail

      • StyleContext

        public StyleContext()
        Creates a new StyleContext object.

    • Method Detail

      • getDefaultStyleContext

        public static final StyleContext getDefaultStyleContext()
        Returns default AttributeContext shared by all documents that don't bother to define/supply their own context.
        Returns:
        the context

      • addStyle

        public Style addStyle​(String nm,
                      Style parent)
        Adds a new style into the style hierarchy. Style attributes resolve from bottom up so an attribute specified in a child will override an attribute specified in the parent.
        Parameters:
        nm - the name of the style (must be unique within the collection of named styles in the document). The name may be null if the style is unnamed, but the caller is responsible for managing the reference returned as an unnamed style can't be fetched by name. An unnamed style may be useful for things like character attribute overrides such as found in a style run.
        parent - the parent style. This may be null if unspecified attributes need not be resolved in some other style.
        Returns:
        the created style

      • removeStyle

        public void removeStyle​(String nm)
        Removes a named style previously added to the document.
        Parameters:
        nm - the name of the style to remove

      • getStyle

        public Style getStyle​(String nm)
        Fetches a named style previously added to the document
        Parameters:
        nm - the name of the style
        Returns:
        the style

      • getStyleNames

        public Enumeration<?> getStyleNames()
        Fetches the names of the styles defined.
        Returns:
        the list of names as an enumeration

      • addChangeListener

        public void addChangeListener​(ChangeListener l)
        Adds a listener to track when styles are added or removed.
        Parameters:
        l - the change listener

      • removeChangeListener

        public void removeChangeListener​(ChangeListener l)
        Removes a listener that was tracking styles being added or removed.
        Parameters:
        l - the change listener

      • getChangeListeners

        public ChangeListener[] getChangeListeners()
        Returns an array of all the ChangeListeners added to this StyleContext with addChangeListener().
        Returns:
        all of the ChangeListeners added or an empty array if no listeners have been added
        Since:
        1.4

      • getFont

        public Font getFont​(AttributeSet attr)
        Gets the font from an attribute set. This is implemented to try and fetch a cached font for the given AttributeSet, and if that fails the font features are resolved and the font is fetched from the low-level font cache.
        Parameters:
        attr - the attribute set
        Returns:
        the font

      • getForeground

        public Color getForeground​(AttributeSet attr)
        Takes a set of attributes and turn it into a foreground color specification. This might be used to specify things like brighter, more hue, etc. By default it simply returns the value specified by the StyleConstants.Foreground attribute.
        Parameters:
        attr - the set of attributes
        Returns:
        the color

      • getBackground

        public Color getBackground​(AttributeSet attr)
        Takes a set of attributes and turn it into a background color specification. This might be used to specify things like brighter, more hue, etc. By default it simply returns the value specified by the StyleConstants.Background attribute.
        Parameters:
        attr - the set of attributes
        Returns:
        the color

      • getFont

        public Font getFont​(String family,
                    int style,
                    int size)
        Gets a new font. This returns a Font from a cache if a cached font exists. If not, a Font is added to the cache. This is basically a low-level cache for 1.1 font features.
        Parameters:
        family - the font family (such as "Monospaced")
        style - the style of the font (such as Font.PLAIN)
        size - the point size >= 1
        Returns:
        the new font

      • getFontMetrics

        public FontMetrics getFontMetrics​(Font f)
        Returns font metrics for a font.
        Parameters:
        f - the font
        Returns:
        the metrics

      • reclaim

        public void reclaim​(AttributeSet a)
        Returns a set no longer needed by the MutableAttributeSet implementation. This is useful for operation under 1.1 where there are no weak references. This would typically be called by the finalize method of the MutableAttributeSet implementation.

        This method is thread safe, although most Swing methods are not. Please see Concurrency in Swing for more information.

        Specified by:
        reclaim in interface AbstractDocument.AttributeContext
        Parameters:
        a - the set to reclaim

      • getCompressionThreshold

        protected int getCompressionThreshold()
        Returns the maximum number of key/value pairs to try and compress into unique/immutable sets. Any sets above this limit will use hashtables and be a MutableAttributeSet.
        Returns:
        the threshold

      • createSmallAttributeSet

        protected StyleContext.SmallAttributeSet createSmallAttributeSet​(AttributeSet a)
        Create a compact set of attributes that might be shared. This is a hook for subclasses that want to alter the behavior of SmallAttributeSet. This can be reimplemented to return an AttributeSet that provides some sort of attribute conversion.
        Parameters:
        a - The set of attributes to be represented in the the compact form.
        Returns:
        a compact set of attributes that might be shared

      • createLargeAttributeSet

        protected MutableAttributeSet createLargeAttributeSet​(AttributeSet a)
        Create a large set of attributes that should trade off space for time. This set will not be shared. This is a hook for subclasses that want to alter the behavior of the larger attribute storage format (which is SimpleAttributeSet by default). This can be reimplemented to return a MutableAttributeSet that provides some sort of attribute conversion.
        Parameters:
        a - The set of attributes to be represented in the the larger form.
        Returns:
        a large set of attributes that should trade off space for time

      • toString

        public String toString()
        Converts a StyleContext to a String.
        Overrides:
        toString in class Object
        Returns:
        the string

      • writeAttributes

        public void writeAttributes​(ObjectOutputStream out,
                            AttributeSet a)
                     throws IOException
        Context-specific handling of writing out attributes
        Parameters:
        out - the output stream
        a - the attribute set
        Throws:
        IOException - on any I/O error

      • writeAttributeSet

        public static void writeAttributeSet​(ObjectOutputStream out,
                                     AttributeSet a)
                              throws IOException
        Writes a set of attributes to the given object stream for the purpose of serialization. This will take special care to deal with static attribute keys that have been registered wit the registerStaticAttributeKey method. Any attribute key not registered as a static key will be serialized directly. All values are expected to be serializable.
        Parameters:
        out - the output stream
        a - the attribute set
        Throws:
        IOException - on any I/O error

      • readAttributeSet

        public static void readAttributeSet​(ObjectInputStream in,
                                    MutableAttributeSet a)
                             throws ClassNotFoundException,
                                    IOException
        Reads a set of attributes from the given object input stream that have been previously written out with writeAttributeSet. This will try to restore keys that were static objects to the static objects in the current virtual machine considering only those keys that have been registered with the registerStaticAttributeKey method. The attributes retrieved from the stream will be placed into the given mutable set.
        Parameters:
        in - the object stream to read the attribute data from.
        a - the attribute set to place the attribute definitions in.
        Throws:
        ClassNotFoundException - passed upward if encountered when reading the object stream.
        IOException - passed upward if encountered when reading the object stream.

      • registerStaticAttributeKey

        public static void registerStaticAttributeKey​(Object key)
        Registers an object as a static object that is being used as a key in attribute sets. This allows the key to be treated specially for serialization.

        For operation under a 1.1 virtual machine, this uses the value returned by toString concatenated to the classname. The value returned by toString should not have the class reference in it (ie it should be reimplemented from the definition in Object) in order to be the same when recomputed later.

        Parameters:
        key - the non-null object key

      • getStaticAttribute

        public static Object getStaticAttribute​(Object key)
        Returns the object previously registered with registerStaticAttributeKey.
        Parameters:
        key - the object key
        Returns:
        Returns the object previously registered with registerStaticAttributeKey