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):
Note that the implementations of these methods are
inefficient, so they are usually overridden with more efficient
toolkit-specific implementations.
When an application asks AWT 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. 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.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.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 method.
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.
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 returntrue. - It is symmetric: for any non-null reference values
xandy,x.equals(y)should returntrueif and only ify.equals(x)returnstrue. - It is transitive: for any non-null reference values
x,y, andz, ifx.equals(y)returnstrueandy.equals(z)returnstrue, thenx.equals(z)should returntrue. - It is consistent: for any non-null reference values
xandy, multiple invocations of x.equals(y) consistently returntrueor consistently returnfalse, provided no information used inequalscomparisons on the objects is modified. - For any non-null reference value
x,x.equals(null)should returnfalse.
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.
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.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.Font described by this
FontMetrics object.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.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.Font
described by this FontMetrics object. No character
extends further above the font's baseline than this height.Graphics context.Font
described by this FontMetrics object. No character
extends further below the font's baseline than this height.Graphics context.
The bounds is used to layout the String
created with the specified array of characters,
beginIndex and limit.CharacterIterator in the
specified Graphics context.String in the
specified Graphics context. The bounds is used
to layout the String.String in the
specified Graphics context. The bounds is used
to layout the String.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.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
hashCodemethod 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.)
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.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
synchronizedstatement 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.
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.
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 total advance width returned from this method
does not take into account the rendering context. Therefore,
the anti-aliasing and fractional metrics hints can affect the
value of the advance. When enabling the anti-aliasing and
fractional metrics hints, use
getStringBounds(String, Graphics)
instead of this method. The advance of a String is
not necessarily the sum of the advances of its characters.
FontMetrics
object's values as a String.
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.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.
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.
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
notifymethod or thenotifyAllmethod. - The timeout period, specified by
timeoutmilliseconds plusnanosnanoseconds 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.