NumberFormat is the abstract base class for all number
formats. This class provides the interface for formatting and parsing
numbers. NumberFormat also provides methods for determining
which locales have number formats, and what their names are.
NumberFormat helps you to format and parse numbers for any locale.
Your code can be completely independent of the locale conventions for
decimal points, thousands-separators, or even the particular decimal
digits used, or whether the number format is even decimal.
To format a number for the current Locale, use one of the factory class methods:
If you are formatting multiple numbers, it is more efficient to get the format and use it multiple times so that the system doesn't have to fetch the information about the local language and country conventions multiple times.myString = NumberFormat.getInstance().format(myNumber);
NumberFormat nf = NumberFormat.getInstance();
for (int i = 0; i < a.length; ++i) {
output.println(nf.format(myNumber[i]) + "; ");
}
To format a number for a different Locale, specify it in the
call to getInstance.
You can also use aNumberFormat nf = NumberFormat.getInstance(Locale.FRENCH);
NumberFormat to parse numbers:
UsemyNumber = nf.parse(myString);
getInstance or getNumberInstance to get the
normal number format. Use getIntegerInstance to get an
integer number format. Use getCurrencyInstance to get the
currency number format. And use getPercentInstance to get a
format for displaying percentages. With this format, a fraction like
0.53 is displayed as 53%.
You can also control the display of numbers with such methods as
setMinimumFractionDigits.
If you want even more control over the format or parsing,
or want to give your users more control,
you can try casting the NumberFormat you get from the factory methods
to a DecimalFormat. This will work for the vast majority
of locales; just remember to put it in a try block in case you
encounter an unusual one.
NumberFormat and DecimalFormat are designed such that some controls work for formatting and others work for parsing. The following is the detailed description for each these control methods,
setParseIntegerOnly : only affects parsing, e.g. if true, "3456.78" -> 3456 (and leaves the parse position just after index 6) if false, "3456.78" -> 3456.78 (and leaves the parse position just after index 8) This is independent of formatting. If you want to not show a decimal point where there might be no digits after the decimal point, use setDecimalSeparatorAlwaysShown.
setDecimalSeparatorAlwaysShown : only affects formatting, and only where there might be no digits after the decimal point, such as with a pattern like "#,##0.##", e.g., if true, 3456.00 -> "3,456." if false, 3456.00 -> "3456" This is independent of parsing. If you want parsing to stop at the decimal point, use setParseIntegerOnly.
You can also use forms of the parse and format
methods with ParsePosition and FieldPosition to
allow you to:
FieldPosition in your format call, with
field = INTEGER_FIELD. On output,
getEndIndex will be set to the offset between the
last character of the integer and the decimal. Add
(desiredSpaceCount - getEndIndex) spaces at the front of the string.
getEndIndex.
Then move the pen by
(desiredPixelWidth - widthToAlignmentPoint) before drawing the text.
It also works where there is no decimal, but possibly additional
characters at the end, e.g., with parentheses in negative
numbers: "(12)" for -12.
Number formats are generally not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.
format
(obj,
new StringBuffer(), new FieldPosition(0)).toString();
This implementation extracts the number's value using
for all integral type values that
can be converted to long without loss of information,
including BigInteger values with a
bit length
of less than 64,
and
for all other types. It
then calls
or
.
This may result in loss of magnitude information and precision for
BigInteger and BigDecimal values.
AttributedCharacterIterator.
You can use the returned AttributedCharacterIterator
to build the resulting String, as well as to determine information
about the resulting String.
Each attribute key of the AttributedCharacterIterator will be of type
Field. It is up to each Format implementation
to define what the legal values are for each attribute in the
AttributedCharacterIterator, but typically the attribute
key is also used as the attribute value.
The default implementation creates an
AttributedCharacterIterator with no attributes. Subclasses
that support fields should override this and create an
AttributedCharacterIterator with meaningful attributes.
get*Instance methods of this class can return
localized instances.
The array returned must contain at least a Locale
instance equal to Locale.US
.
The default implementation throws
UnsupportedOperationException.
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:
synchronized statement
that synchronizes on the object.
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.
Number.
The method attempts to parse text starting at the index given by
pos.
If parsing succeeds, then the index of pos is updated
to the index after the last character used (parsing does not necessarily
use all characters up to the end of the string), and the parsed
number is returned. The updated pos can be used to
indicate the starting point for the next call to this method.
If an error occurs, then the index of pos is not
changed, the error index of pos is set to the index of
the character where the error occurred, and null is returned.
The default implementation throws
UnsupportedOperationException.
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())
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:
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:
notify method
or the notifyAll method.
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.