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Class Image

java.lang.Object
java.awt.Image
Direct Known Subclasses:
AbstractMultiResolutionImage, BufferedImage, VolatileImage 
public abstract class Image extends Object
The abstract class Image is the superclass of all classes that represent graphical images. The image must be obtained in a platform-specific manner.
Since:
1.0

Field Summary

Modifier and Type Field Description
protected float accelerationPriority
Priority for accelerating this image.
static final int SCALE_AREA_AVERAGING
Use the Area Averaging image scaling algorithm.
static final int SCALE_DEFAULT
Use the default image-scaling algorithm.
static final int SCALE_FAST
Choose an image-scaling algorithm that gives higher priority to scaling speed than smoothness of the scaled image.
static final int SCALE_REPLICATE
Use the image scaling algorithm embodied in the ReplicateScaleFilter class.
static final int SCALE_SMOOTH
Choose an image-scaling algorithm that gives higher priority to image smoothness than scaling speed.
static final Object UndefinedProperty
The UndefinedProperty object should be returned whenever a property which was not defined for a particular image is fetched.

Constructor Summary

Image()
Modifier Constructor Description
protected
Constructor for subclasses to call.

Method Summary

Modifier and Type Method Description
void flush()
Flushes all reconstructable resources being used by this Image object.
float getAccelerationPriority()
Returns the current value of the acceleration priority hint.
ImageCapabilities getCapabilities(GraphicsConfiguration gc)
Returns an ImageCapabilities object which can be inquired as to the capabilities of this Image on the specified GraphicsConfiguration.
abstract Graphics getGraphics()
Creates a graphics context for drawing to an off-screen image.
abstract int getHeight(ImageObserver observer)
Determines the height of the image.
abstract Object getProperty(String name, ImageObserver observer)
Gets a property of this image by name.
Image getScaledInstance(int width, int height, int hints)
Creates a scaled version of this image.
abstract ImageProducer getSource()
Gets the object that produces the pixels for the image.
abstract int getWidth(ImageObserver observer)
Determines the width of the image.
void setAccelerationPriority(float priority)
Sets a hint for this image about how important acceleration is.

Methods declared in class java.lang.Object

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

Field Details

accelerationPriority

protected float accelerationPriority
Priority for accelerating this image. Subclasses are free to set different default priorities and applications are free to set the priority for specific images via the setAccelerationPriority(float) method.
Since:
1.5

UndefinedProperty

public static final Object UndefinedProperty
The UndefinedProperty object should be returned whenever a property which was not defined for a particular image is fetched.

SCALE_DEFAULT

public static final int SCALE_DEFAULT
Use the default image-scaling algorithm.
Since:
1.1
See Also:

SCALE_FAST

public static final int SCALE_FAST
Choose an image-scaling algorithm that gives higher priority to scaling speed than smoothness of the scaled image.
Since:
1.1
See Also:

SCALE_SMOOTH

public static final int SCALE_SMOOTH
Choose an image-scaling algorithm that gives higher priority to image smoothness than scaling speed.
Since:
1.1
See Also:

SCALE_REPLICATE

public static final int SCALE_REPLICATE
Use the image scaling algorithm embodied in the ReplicateScaleFilter class. The Image object is free to substitute a different filter that performs the same algorithm yet integrates more efficiently into the imaging infrastructure supplied by the toolkit.
Since:
1.1
See Also:

SCALE_AREA_AVERAGING

public static final int SCALE_AREA_AVERAGING
Use the Area Averaging image scaling algorithm. The image object is free to substitute a different filter that performs the same algorithm yet integrates more efficiently into the image infrastructure supplied by the toolkit.
Since:
1.1
See Also:

Constructor Details

Image

protected Image()
Constructor for subclasses to call.

Method Details

getWidth

public abstract int getWidth(ImageObserver observer)
Determines the width of the image. If the width is not yet known, this method returns -1 and the specified ImageObserver object is notified later.
Parameters:
observer - an object waiting for the image to be loaded.
Returns:
the width of this image, or -1 if the width is not yet known.
See Also:

getHeight

public abstract int getHeight(ImageObserver observer)
Determines the height of the image. If the height is not yet known, this method returns -1 and the specified ImageObserver object is notified later.
Parameters:
observer - an object waiting for the image to be loaded.
Returns:
the height of this image, or -1 if the height is not yet known.
See Also:

getSource

public abstract ImageProducer getSource()
Gets the object that produces the pixels for the image. This method is called by the image filtering classes and by methods that perform image conversion and scaling.
Returns:
the image producer that produces the pixels for this image.
See Also:

getGraphics

public abstract Graphics getGraphics()
Creates a graphics context for drawing to an off-screen image. This method can only be called for off-screen images.
Returns:
a graphics context to draw to the off-screen image.
Throws:
UnsupportedOperationException - if called for a non-off-screen image.
See Also:

getProperty

public abstract Object getProperty(String name, ImageObserver observer)
Gets a property of this image by name.

Individual property names are defined by the various image formats. If a property is not defined for a particular image, this method returns the UndefinedProperty object.

If the properties for this image are not yet known, this method returns null, and the ImageObserver object is notified later.

The property name "comment" should be used to store an optional comment which can be presented to the application as a description of the image, its source, or its author.

Parameters:
name - a property name.
observer - an object waiting for this image to be loaded.
Returns:
the value of the named property.
Throws:
NullPointerException - if the property name is null.
See Also:

getScaledInstance

public Image getScaledInstance(int width, int height, int hints)
Creates a scaled version of this image. A new Image object is returned which will render the image at the specified width and height by default. The new Image object may be loaded asynchronously even if the original source image has already been loaded completely.

If either width or height is a negative number then a value is substituted to maintain the aspect ratio of the original image dimensions. If both width and height are negative, then the original image dimensions are used.

Parameters:
width - the width to which to scale the image.
height - the height to which to scale the image.
hints - flags to indicate the type of algorithm to use for image resampling.
Returns:
a scaled version of the image.
Throws:
IllegalArgumentException - if width or height is zero.
Since:
1.1
See Also:

flush

public void flush()
Flushes all reconstructable resources being used by this Image object. This includes any pixel data that is being cached for rendering to the screen as well as any system resources that are being used to store data or pixels for the image if they can be recreated. The image is reset to a state similar to when it was first created so that if it is again rendered, the image data will have to be recreated or fetched again from its source.

Examples of how this method affects specific types of Image object:

  • BufferedImage objects leave the primary Raster which stores their pixels untouched, but flush any information cached about those pixels such as copies uploaded to the display hardware for accelerated blits.
  • Image objects created by the Component methods which take a width and height leave their primary buffer of pixels untouched, but have all cached information released much like is done for BufferedImage objects.
  • VolatileImage objects release all of their pixel resources including their primary copy which is typically stored on the display hardware where resources are scarce. These objects can later be restored using their validate method.
  • Image objects created by the Toolkit and Component classes which are loaded from files, URLs or produced by an ImageProducer are unloaded and all local resources are released. These objects can later be reloaded from their original source as needed when they are rendered, just as when they were first created.

getCapabilities

public ImageCapabilities getCapabilities(GraphicsConfiguration gc)
Returns an ImageCapabilities object which can be inquired as to the capabilities of this Image on the specified GraphicsConfiguration. This allows programmers to find out more runtime information on the specific Image object that they have created. For example, the user might create a BufferedImage but the system may have no video memory left for creating an image of that size on the given GraphicsConfiguration, so although the object may be acceleratable in general, it does not have that capability on this GraphicsConfiguration.
Parameters:
gc - a GraphicsConfiguration object. A value of null for this parameter will result in getting the image capabilities for the default GraphicsConfiguration.
Returns:
an ImageCapabilities object that contains the capabilities of this Image on the specified GraphicsConfiguration.
Since:
1.5
See Also:

setAccelerationPriority

public void setAccelerationPriority(float priority)
Sets a hint for this image about how important acceleration is. This priority hint is used to compare to the priorities of other Image objects when determining how to use scarce acceleration resources such as video memory. When and if it is possible to accelerate this Image, if there are not enough resources available to provide that acceleration but enough can be freed up by de-accelerating some other image of lower priority, then that other Image may be de-accelerated in deference to this one. Images that have the same priority take up resources on a first-come, first-served basis.
Parameters:
priority - a value between 0 and 1, inclusive, where higher values indicate more importance for acceleration. A value of 0 means that this Image should never be accelerated. Other values are used simply to determine acceleration priority relative to other Images.
Throws:
IllegalArgumentException - if priority is less than zero or greater than 1.
Since:
1.5

getAccelerationPriority

public float getAccelerationPriority()
Returns the current value of the acceleration priority hint.
Returns:
value between 0 and 1, inclusive, which represents the current priority value
Since:
1.5
See Also:

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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