A very important part of the text package is the View class. As the name suggests it represents a view of the text model, or a piece of the text model. It is this class that is responsible for the look of the text component. The view is not intended to be some completely new thing that one must learn, but rather is much like a lightweight component. In fact, the original View implementation was a lightweight component. There were several reasons why the Component implementation was abandoned in favor of an alternative.

  1. There was barely time to get the lightweight component support in the 1.1 version of the JDK. There simply wasn't time to lighten up the component further to where it would need to be to be used for text purposes. The additions made to JComponent increased the memory consumption, and as it currently stands its much too heavy for representing text.

  2. The layout semantics aren't quite right for text, and changing the current layout semantics of component might break existing applications.

  3. The component api uses integers, but in 1.2 one can use floating point device independent coordinates. An api that works in both 1.1 and 1.2 would be convenient for minimizing transition difficulties. The View class uses the Shape interface and float arguments to enable View implementations for the Java 2 platform v1.2 and later while still functioning in the older 1.1 JDK.

By default, a view is very light. It contains a reference to the parent view from which it can fetch many things without holding state, and it contains a reference to a portion of the model (Element). A view does not have to exactly represent an element in the model, that is simply a typical and therefore convenient mapping. A view can alternatively maintain a couple of Position objects to maintain its location in the model (i.e. represent a fragment of an element). This is typically the result of formatting where views have been broken down into pieces. The convenience of a substantial relationship to the element makes it easier to build factories to produce the views, and makes it easier to keep track of the view pieces as the model is changed and the view must be changed to reflect the model. Simple views therefore represent an Element directly and complex views do not.

A view has the following responsibilities:

Participate in layout.

The view has a setSize method which is like doLayout and setSize in Component combined. The view has a preferenceChanged method which is like invalidate in Component except that one can invalidate just one axis and the child requesting the change is identified.

A View expresses the size that it would like to be in terms of three values, a minimum, a preferred, and a maximum span. Layout in a view is can be done independently upon each axis. For a properly functioning View implementation, the minimum span will be <= the preferred span which in turn will be <= the maximum span.

The above text describes this graphic.

The minimum set of methods for layout are:

The setSize method should be prepared to be called a number of times (i.e. It may be called even if the size didn't change). The setSize method is generally called to make sure the View layout is complete prior to trying to perform an operation on it that requires an up-to-date layout. A view's size should always be set to a value within the minimum and maximum span specified by that view. Additionally, the view must always call the preferenceChanged method on the parent if it has changed the values for the layout it would like, and expects the parent to honor. The parent View is not required to recognize a change until the preferenceChanged has been sent. This allows parent View implementations to cache the child requirements if desired. The calling sequence looks something like the following:

Sample calling sequence between parent view and child view: 
       setSize, getMinimum, getPreferred, getMaximum, getAlignment, setSize

The exact calling sequence is up to the layout functionality of the parent view (if the view has any children). The view may collect the preferences of the children prior to determining what it will give each child, or it might iteratively update the children one at a time.

Render a portion of the model.

This is done in the paint method, which is pretty much like a component paint method. Views are expected to potentially populate a fairly large tree. A View has the following semantics for rendering:

  • The view gets its allocation from the parent at paint time, so it must be prepared to redo layout if the allocated area is different from what it is prepared to deal with.
  • The coordinate system is the same as the hosting Component (i.e. the Component returned by the getContainer method). This means a child view lives in the same coordinate system as the parent view unless the parent has explicitly changed the coordinate system. To schedule itself to be repainted a view can call repaint on the hosting Component.
  • The default is to not clip the children. It is more efficient to allow a view to clip only if it really feels it needs clipping.
  • The Graphics object given is not initialized in any way. A view should set any settings needed.
  • A View is inherently transparent. While a view may render into its entire allocation, typically a view does not. Rendering is performed by tranversing down the tree of View implementations. Each View is responsible for rendering its children. This behavior is depended upon for thread safety. While view implementations do not necessarily have to be implemented with thread safety in mind, other view implementations that do make use of concurrency can depend upon a tree traversal to guarantee thread safety.
  • The order of views relative to the model is up to the implementation. Although child views will typically be arranged in the same order that they occur in the model, they may be visually arranged in an entirely different order. View implementations may have Z-Order associated with them if the children are overlapping.

The methods for rendering are:

Translate between the model and view coordinate systems.

Because the view objects are produced from a factory and therefore cannot necessarily be counted upon to be in a particular pattern, one must be able to perform translation to properly locate spatial representation of the model. The methods for doing this are:

The layout must be valid prior to attempting to make the translation. The translation is not valid, and must not be attempted while changes are being broadcasted from the model via a DocumentEvent.

Respond to changes from the model.

If the overall view is represented by many pieces (which is the best situation if one want to be able to change the view and write the least amount of new code), it would be impractical to have a huge number of DocumentListeners. If each view listened to the model, only a few would actually be interested in the changes broadcasted at any given time. Since the model has no knowledge of views, it has no way to filter the broadcast of change information. The view hierarchy itself is instead responsible for propagating the change information. At any level in the view hierarchy, that view knows enough about its children to best distribute the change information further. Changes are therefore broadcasted starting from the root of the view hierarchy. The methods for doing this are:

@author
Timothy Prinzing
@version
1.70 05/18/04
Creates a new View object.
Parameters
elemthe Element to represent
The weight to indicate a view is a bad break opportunity for the purpose of formatting. This value indicates that no attempt should be made to break the view into fragments as the view has not been written to support fragmenting.
Box-orientation constant used to specify the bottom of a box.
The central position in an area. Used for both compass-direction constants (NORTH, etc.) and box-orientation constants (TOP, etc.).
Compass-direction east (right).
The weight to indicate a view supports breaking, and this represents a very attractive place to break.
The weight to indicate a view supports breaking, and must be broken to be represented properly when placed in a view that formats its children by breaking them.
The weight to indicate a view supports breaking, but better opportunities probably exist.
Horizontal orientation. Used for scrollbars and sliders.
Identifies the leading edge of text for use with left-to-right and right-to-left languages. Used by buttons and labels.
Box-orientation constant used to specify the left side of a box.
Identifies the next direction in a sequence.
@since
1.4
Compass-direction North (up).
Compass-direction north-east (upper right).
Compass-direction north west (upper left).
Identifies the previous direction in a sequence.
@since
1.4
Box-orientation constant used to specify the right side of a box.
Compass-direction south (down).
Compass-direction south-east (lower right).
Compass-direction south-west (lower left).
Box-orientation constant used to specify the top of a box.
Identifies the trailing edge of text for use with left-to-right and right-to-left languages. Used by buttons and labels.
Vertical orientation. Used for scrollbars and sliders.
Compass-direction west (left).
Axis for format/break operations.
Axis for format/break operations.
Appends a single child view. This is a convenience call to replace.
Parameters
vthe view
@since
1.3
See Also
Tries to break this view on the given axis. This is called by views that try to do formatting of their children. For example, a view of a paragraph will typically try to place its children into row and views representing chunks of text can sometimes be broken down into smaller pieces.

This is implemented to return the view itself, which represents the default behavior on not being breakable. If the view does support breaking, the starting offset of the view returned should be the given offset, and the end offset should be less than or equal to the end offset of the view being broken.

Parameters
axismay be either View.X_AXIS or View.Y_AXIS
offsetthe location in the document model that a broken fragment would occupy >= 0. This would be the starting offset of the fragment returned
posthe position along the axis that the broken view would occupy >= 0. This may be useful for things like tab calculations
lenspecifies the distance along the axis where a potential break is desired >= 0
Return
the fragment of the view that represents the given span, if the view can be broken. If the view doesn't support breaking behavior, the view itself is returned.
See Also
Gives notification from the document that attributes were changed in a location that this view is responsible for. To reduce the burden to subclasses, this functionality is spread out into the following calls that subclasses can reimplement:
  1. updateChildren is called if there were any changes to the element this view is responsible for. If this view has child views that are represent the child elements, then this method should do whatever is necessary to make sure the child views correctly represent the model.
  2. forwardUpdate is called to forward the DocumentEvent to the appropriate child views.
  3. updateLayout is called to give the view a chance to either repair its layout, to reschedule layout, or do nothing.
Parameters
ethe change information from the associated document
athe current allocation of the view
fthe factory to use to rebuild if the view has children
Creates a view that represents a portion of the element. This is potentially useful during formatting operations for taking measurements of fragments of the view. If the view doesn't support fragmenting (the default), it should return itself.
Parameters
p0the starting offset >= 0. This should be a value greater or equal to the element starting offset and less than the element ending offset.
p1the ending offset > p0. This should be a value less than or equal to the elements end offset and greater than the elements starting offset.
Return
the view fragment, or itself if the view doesn't support breaking into fragments
See Also
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

  • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

Parameters
objthe reference object with which to compare.
Return
true if this object is the same as the obj argument; false otherwise.
Determines the desired alignment for this view along an axis. The desired alignment is returned. This should be a value >= 0.0 and <= 1.0, where 0 indicates alignment at the origin and 1.0 indicates alignment to the full span away from the origin. An alignment of 0.5 would be the center of the view.
Parameters
axismay be either View.X_AXIS or View.Y_AXIS
Return
the value 0.5
Fetches the attributes to use when rendering. By default this simply returns the attributes of the associated element. This method should be used rather than using the element directly to obtain access to the attributes to allow view-specific attributes to be mixed in or to allow the view to have view-specific conversion of attributes by subclasses. Each view should document what attributes it recognizes for the purpose of rendering or layout, and should always access them through the AttributeSet returned by this method.
Determines how attractive a break opportunity in this view is. This can be used for determining which view is the most attractive to call breakView on in the process of formatting. A view that represents text that has whitespace in it might be more attractive than a view that has no whitespace, for example. The higher the weight, the more attractive the break. A value equal to or lower than BadBreakWeight should not be considered for a break. A value greater than or equal to ForcedBreakWeight should be broken.

This is implemented to provide the default behavior of returning BadBreakWeight unless the length is greater than the length of the view in which case the entire view represents the fragment. Unless a view has been written to support breaking behavior, it is not attractive to try and break the view. An example of a view that does support breaking is LabelView. An example of a view that uses break weight is ParagraphView.

Parameters
axismay be either View.X_AXIS or View.Y_AXIS
posthe potential location of the start of the broken view >= 0. This may be useful for calculating tab positions
lenspecifies the relative length from pos where a potential break is desired >= 0
Return
the weight, which should be a value between ForcedBreakWeight and BadBreakWeight
Fetches the allocation for the given child view. This enables finding out where various views are located, without assuming how the views store their location. This returns null since the default is to not have any child views.
Parameters
indexthe index of the child, >= 0 && < getViewCount()
athe allocation to this view
Return
the allocation to the child
Returns the runtime class of an object. That Class object is the object that is locked by static synchronized methods of the represented class.
Return
The java.lang.Class object that represents the runtime class of the object. The result is of type {@code Class} where X is the erasure of the static type of the expression on which getClass is called.
Fetches the container hosting the view. This is useful for things like scheduling a repaint, finding out the host components font, etc. The default implementation of this is to forward the query to the parent view.
Return
the container, null if none
Fetches the model associated with the view.
Return
the view model, null if none
Fetches the structural portion of the subject that this view is mapped to. The view may not be responsible for the entire portion of the element.
Return
the subject
Fetches the portion of the model for which this view is responsible.
Return
the ending offset into the model >= 0
Fetch a Graphics for rendering. This can be used to determine font characteristics, and will be different for a print view than a component view.
Return
a Graphics object for rendering
@since
1.3
Determines the maximum span for this view along an axis.
Parameters
axismay be either View.X_AXIS or View.Y_AXIS
Return
the maximum span the view can be rendered into
Determines the minimum span for this view along an axis.
Parameters
axismay be either View.X_AXIS or View.Y_AXIS
Return
the minimum span the view can be rendered into
Provides a way to determine the next visually represented model location at which one might place a caret. Some views may not be visible, they might not be in the same order found in the model, or they just might not allow access to some of the locations in the model.
Parameters
posthe position to convert >= 0
athe allocated region in which to render
directionthe direction from the current position that can be thought of as the arrow keys typically found on a keyboard. This will be one of the following values:
  • SwingConstants.WEST
  • SwingConstants.EAST
  • SwingConstants.NORTH
  • SwingConstants.SOUTH
Return
the location within the model that best represents the next location visual position
Throws
BadLocationException
IllegalArgumentExceptionif direction doesn't have one of the legal values above
Returns the parent of the view.
Return
the parent, or null if none exists
Determines the preferred span for this view along an axis.
Parameters
axismay be either View.X_AXIS or View.Y_AXIS
Return
the span the view would like to be rendered into. Typically the view is told to render into the span that is returned, although there is no guarantee. The parent may choose to resize or break the view
Determines the resizability of the view along the given axis. A value of 0 or less is not resizable.
Parameters
axismay be either View.X_AXIS or View.Y_AXIS
Return
the weight
Fetches the portion of the model for which this view is responsible.
Return
the starting offset into the model >= 0
Returns the tooltip text at the specified location. The default implementation returns the value from the child View identified by the passed in location.
@since
1.4
Gets the nth child view. Since there are no children by default, this returns null.
Parameters
nthe number of the view to get, >= 0 && < getViewCount()
Return
the view
Returns the number of views in this view. Since the default is to not be a composite view this returns 0.
Return
the number of views >= 0
Fetches the ViewFactory implementation that is feeding the view hierarchy. Normally the views are given this as an argument to updates from the model when they are most likely to need the factory, but this method serves to provide it at other times.
Return
the factory, null if none
Returns the child view index representing the given position in the view. This iterates over all the children returning the first with a bounds that contains x, y.
Parameters
xthe x coordinate
ythe y coordinate
allocationcurrent allocation of the View.
Return
index of the view representing the given location, or -1 if no view represents that position
@since
1.4
Returns the child view index representing the given position in the model. By default a view has no children so this is implemented to return -1 to indicate there is no valid child index for any position.
Parameters
posthe position >= 0
Return
index of the view representing the given position, or -1 if no view represents that position
@since
1.3
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Return
a hash code value for this object.
Inserts a single child view. This is a convenience call to replace.
Parameters
offsthe offset of the view to insert before >= 0
vthe view
@since
1.3
See Also
Gives notification that something was inserted into the document in a location that this view is responsible for. To reduce the burden to subclasses, this functionality is spread out into the following calls that subclasses can reimplement:
  1. updateChildren is called if there were any changes to the element this view is responsible for. If this view has child views that are represent the child elements, then this method should do whatever is necessary to make sure the child views correctly represent the model.
  2. forwardUpdate is called to forward the DocumentEvent to the appropriate child views.
  3. updateLayout is called to give the view a chance to either repair its layout, to reschedule layout, or do nothing.
Parameters
ethe change information from the associated document
athe current allocation of the view
fthe factory to use to rebuild if the view has children
Returns a boolean that indicates whether the view is visible or not. By default all views are visible.
Return
always returns true
Provides a mapping, for a given region, from the document model coordinate space to the view coordinate space. The specified region is created as a union of the first and last character positions.
Parameters
p0the position of the first character (>=0)
b0the bias of the first character position, toward the previous character or the next character represented by the offset, in case the position is a boundary of two views; b0 will have one of these values:
  • Position.Bias.Forward
  • Position.Bias.Backward
p1the position of the last character (>=0)
b1the bias for the second character position, defined one of the legal values shown above
athe area of the view, which encompasses the requested region
Return
the bounding box which is a union of the region specified by the first and last character positions
Throws
BadLocationExceptionif the given position does not represent a valid location in the associated document
IllegalArgumentExceptionif b0 or b1 are not one of the legal Position.Bias values listed above
Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it. This is implemented to default the bias to Position.Bias.Forward which was previously implied.
Parameters
posthe position to convert >= 0
athe allocated region in which to render
Return
the bounding box of the given position is returned
Throws
BadLocationExceptionif the given position does not represent a valid location in the associated document
@deprecated
Provides a mapping, for a given character, from the document model coordinate space to the view coordinate space.
Parameters
posthe position of the desired character (>=0)
athe area of the view, which encompasses the requested character
bthe bias toward the previous character or the next character represented by the offset, in case the position is a boundary of two views; b will have one of these values:
  • Position.Bias.Forward
  • Position.Bias.Backward
Return
the bounding box, in view coordinate space, of the character at the specified position
Throws
BadLocationExceptionif the specified position does not represent a valid location in the associated document
IllegalArgumentExceptionif b is not one of the legal Position.Bias values listed above
Wakes up a single thread that is waiting on this object's monitor. If any threads are waiting on this object, one of them is chosen to be awakened. The choice is arbitrary and occurs at the discretion of the implementation. A thread waits on an object's monitor by calling one of the wait methods.

The awakened thread will not be able to proceed until the current thread relinquishes the lock on this object. The awakened thread will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened thread enjoys no reliable privilege or disadvantage in being the next thread to lock this object.

This method should only be called by a thread that is the owner of this object's monitor. A thread becomes the owner of the object's monitor in one of three ways:

  • By executing a synchronized instance method of that object.
  • By executing the body of a synchronized statement that synchronizes on the object.
  • For objects of type Class, by executing a synchronized static method of that class.

Only one thread at a time can own an object's monitor.

Throws
IllegalMonitorStateExceptionif the current thread is not the owner of this object's monitor.
Wakes up all threads that are waiting on this object's monitor. A thread waits on an object's monitor by calling one of the wait methods.

The awakened threads will not be able to proceed until the current thread relinquishes the lock on this object. The awakened threads will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened threads enjoy no reliable privilege or disadvantage in being the next thread to lock this object.

This method should only be called by a thread that is the owner of this object's monitor. See the notify method for a description of the ways in which a thread can become the owner of a monitor.

Throws
IllegalMonitorStateExceptionif the current thread is not the owner of this object's monitor.
Renders using the given rendering surface and area on that surface. The view may need to do layout and create child views to enable itself to render into the given allocation.
Parameters
gthe rendering surface to use
allocationthe allocated region to render into
See Also
Child views can call this on the parent to indicate that the preference has changed and should be reconsidered for layout. By default this just propagates upward to the next parent. The root view will call revalidate on the associated text component.
Parameters
childthe child view
widthtrue if the width preference has changed
heighttrue if the height preference has changed
Removes one of the children at the given position. This is a convenience call to replace.
@since
1.3
Removes all of the children. This is a convenience call to replace.
@since
1.3
Gives notification that something was removed from the document in a location that this view is responsible for. To reduce the burden to subclasses, this functionality is spread out into the following calls that subclasses can reimplement:
  1. updateChildren is called if there were any changes to the element this view is responsible for. If this view has child views that are represent the child elements, then this method should do whatever is necessary to make sure the child views correctly represent the model.
  2. forwardUpdate is called to forward the DocumentEvent to the appropriate child views.
  3. updateLayout is called to give the view a chance to either repair its layout, to reschedule layout, or do nothing.
Parameters
ethe change information from the associated document
athe current allocation of the view
fthe factory to use to rebuild if the view has children
Replaces child views. If there are no views to remove this acts as an insert. If there are no views to add this acts as a remove. Views being removed will have the parent set to null, and the internal reference to them removed so that they can be garbage collected. This is implemented to do nothing, because by default a view has no children.
Parameters
offsetthe starting index into the child views to insert the new views. This should be a value >= 0 and <= getViewCount
lengththe number of existing child views to remove This should be a value >= 0 and <= (getViewCount() - offset).
viewsthe child views to add. This value can be null to indicate no children are being added (useful to remove).
@since
1.3
Establishes the parent view for this view. This is guaranteed to be called before any other methods if the parent view is functioning properly. This is also the last method called, since it is called to indicate the view has been removed from the hierarchy as well. When this method is called to set the parent to null, this method does the same for each of its children, propogating the notification that they have been disconnected from the view tree. If this is reimplemented, super.setParent() should be called.
Parameters
parentthe new parent, or null if the view is being removed from a parent
Sets the size of the view. This should cause layout of the view along the given axis, if it has any layout duties.
Parameters
widththe width >= 0
heightthe height >= 0
Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 
Return
a string representation of the object.
Provides a mapping from the view coordinate space to the logical coordinate space of the model.
Parameters
xthe X coordinate >= 0
ythe Y coordinate >= 0
athe allocated region in which to render
Return
the location within the model that best represents the given point in the view >= 0
@deprecated
Provides a mapping from the view coordinate space to the logical coordinate space of the model. The biasReturn argument will be filled in to indicate that the point given is closer to the next character in the model or the previous character in the model.
Parameters
xthe X coordinate >= 0
ythe Y coordinate >= 0
athe allocated region in which to render
Return
the location within the model that best represents the given point in the view >= 0. The biasReturn argument will be filled in to indicate that the point given is closer to the next character in the model or the previous character in the model.
Causes current thread to wait until another thread invokes the method or the method for this object. In other words, this method behaves exactly as if it simply performs the call wait(0).

The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until another thread notifies threads waiting on this object's monitor to wake up either through a call to the notify method or the notifyAll method. The thread then waits until it can re-obtain ownership of the monitor and resumes execution.

As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:

     synchronized (obj) {
         while (<condition does not hold>)
             obj.wait();
         ... // Perform action appropriate to condition
     }
 
This method should only be called by a thread that is the owner of this object's monitor. See the notify method for a description of the ways in which a thread can become the owner of a monitor.
Throws
IllegalMonitorStateExceptionif the current thread is not the owner of the object's monitor.
InterruptedExceptionif another thread interrupted the current thread before or while the current thread was waiting for a notification. The interrupted status of the current thread is cleared when this exception is thrown.
Causes current thread to wait until either another thread invokes the method or the method for this object, or a specified amount of time has elapsed.

The current thread must own this object's monitor.

This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. Thread T becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:

  • Some other thread invokes the notify method for this object and thread T happens to be arbitrarily chosen as the thread to be awakened.
  • Some other thread invokes the notifyAll method for this object.
  • Some other thread interrupts thread T.
  • The specified amount of real time has elapsed, more or less. If timeout is zero, however, then real time is not taken into consideration and the thread simply waits until notified.
The thread T is then removed from the wait set for this object and re-enabled for thread scheduling. It then competes in the usual manner with other threads for the right to synchronize on the object; once it has gained control of the object, all its synchronization claims on the object are restored to the status quo ante - that is, to the situation as of the time that the wait method was invoked. Thread T then returns from the invocation of the wait method. Thus, on return from the wait method, the synchronization state of the object and of thread T is exactly as it was when the wait method was invoked.

A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one:

     synchronized (obj) {
         while (<condition does not hold>)
             obj.wait(timeout);
         ... // Perform action appropriate to condition
     }
 
(For more information on this topic, see Section 3.2.3 in Doug Lea's "Concurrent Programming in Java (Second Edition)" (Addison-Wesley, 2000), or Item 50 in Joshua Bloch's "Effective Java Programming Language Guide" (Addison-Wesley, 2001).

If the current thread is interrupted by another thread while it is waiting, then an InterruptedException is thrown. This exception is not thrown until the lock status of this object has been restored as described above.

Note that the wait method, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits.

This method should only be called by a thread that is the owner of this object's monitor. See the notify method for a description of the ways in which a thread can become the owner of a monitor.

Parameters
timeoutthe maximum time to wait in milliseconds.
Throws
IllegalArgumentExceptionif the value of timeout is negative.
IllegalMonitorStateExceptionif the current thread is not the owner of the object's monitor.
InterruptedExceptionif another thread interrupted the current thread before or while the current thread was waiting for a notification. The interrupted status of the current thread is cleared when this exception is thrown.
Causes current thread to wait until another thread invokes the method or the method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.

This method is similar to the wait method of one argument, but it allows finer control over the amount of time to wait for a notification before giving up. The amount of real time, measured in nanoseconds, is given by:

 1000000*timeout+nanos

In all other respects, this method does the same thing as the method of one argument. In particular, wait(0, 0) means the same thing as wait(0).

The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until either of the following two conditions has occurred:

  • Another thread notifies threads waiting on this object's monitor to wake up either through a call to the notify method or the notifyAll method.
  • The timeout period, specified by timeout milliseconds plus nanos nanoseconds arguments, has elapsed.

The thread then waits until it can re-obtain ownership of the monitor and resumes execution.

As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:

     synchronized (obj) {
         while (<condition does not hold>)
             obj.wait(timeout, nanos);
         ... // Perform action appropriate to condition
     }
 
This method should only be called by a thread that is the owner of this object's monitor. See the notify method for a description of the ways in which a thread can become the owner of a monitor.
Parameters
timeoutthe maximum time to wait in milliseconds.
nanosadditional time, in nanoseconds range 0-999999.
Throws
IllegalArgumentExceptionif the value of timeout is negative or the value of nanos is not in the range 0-999999.
IllegalMonitorStateExceptionif the current thread is not the owner of this object's monitor.
InterruptedExceptionif another thread interrupted the current thread before or while the current thread was waiting for a notification. The interrupted status of the current thread is cleared when this exception is thrown.