String for example, your program can load it
from the resource bundle that is appropriate for the
current user's locale. In this way, you can write
program code that is largely independent of the user's
locale isolating most, if not all, of the locale-specific
information in resource bundles.
This allows you to write programs that can:
Resource bundles belong to families whose members share a common base name, but whose names also have additional components that identify their locales. For example, the base name of a family of resource bundles might be "MyResources". The family should have a default resource bundle which simply has the same name as its family - "MyResources" - and will be used as the bundle of last resort if a specific locale is not supported. The family can then provide as many locale-specific members as needed, for example a German one named "MyResources_de".
Each resource bundle in a family contains the same items, but the items have
been translated for the locale represented by that resource bundle.
For example, both "MyResources" and "MyResources_de" may have a
String that's used on a button for canceling operations.
In "MyResources" the String may contain "Cancel" and in
"MyResources_de" it may contain "Abbrechen".
If there are different resources for different countries, you can make specializations: for example, "MyResources_de_CH" contains objects for the German language (de) in Switzerland (CH). If you want to only modify some of the resources in the specialization, you can do so.
When your program needs a locale-specific object, it loads
the ResourceBundle class using the
getBundle
method:
ResourceBundle myResources =
ResourceBundle.getBundle("MyResources", currentLocale);
Resource bundles contain key/value pairs. The keys uniquely
identify a locale-specific object in the bundle. Here's an
example of a ListResourceBundle that contains
two key/value pairs:
public class MyResources extends ListResourceBundle {
public Object[][] getContents() {
return contents;
}
static final Object[][] contents = {
// LOCALIZE THIS
{"OkKey", "OK"},
{"CancelKey", "Cancel"},
// END OF MATERIAL TO LOCALIZE
};
}
Keys are always Strings.
In this example, the keys are "OkKey" and "CancelKey".
In the above example, the values
are also Strings--"OK" and "Cancel"--but
they don't have to be. The values can be any type of object.
You retrieve an object from resource bundle using the appropriate
getter method. Because "OkKey" and "CancelKey"
are both strings, you would use getString to retrieve them:
button1 = new Button(myResources.getString("OkKey"));
button2 = new Button(myResources.getString("CancelKey"));
The getter methods all require the key as an argument and return
the object if found. If the object is not found, the getter method
throws a MissingResourceException.
Besides getString, ResourceBundle also provides
a method for getting string arrays, getStringArray,
as well as a generic getObject method for any other
type of object. When using getObject, you'll
have to cast the result to the appropriate type. For example:
int[] myIntegers = (int[]) myResources.getObject("intList");
The Java 2 platform provides two subclasses of ResourceBundle,
ListResourceBundle and PropertyResourceBundle,
that provide a fairly simple way to create resources.
As you saw briefly in a previous example, ListResourceBundle
manages its resource as a List of key/value pairs.
PropertyResourceBundle uses a properties file to manage
its resources.
If ListResourceBundle or PropertyResourceBundle
do not suit your needs, you can write your own ResourceBundle
subclass. Your subclasses must override two methods: handleGetObject
and getKeys().
The following is a very simple example of a ResourceBundle
subclass, MyResources, that manages two resources (for a larger number of
resources you would probably use a Hashtable).
Notice that you don't need to supply a value if
a "parent-level" ResourceBundle handles the same
key with the same value (as for the okKey below).
Example:
// default (English language, United States)
public class MyResources extends ResourceBundle {
public Object handleGetObject(String key) {
if (key.equals("okKey")) return "Ok";
if (key.equals("cancelKey")) return "Cancel";
return null;
}
}
// German language
public class MyResources_de extends MyResources {
public Object handleGetObject(String key) {
// don't need okKey, since parent level handles it.
if (key.equals("cancelKey")) return "Abbrechen";
return null;
}
}
You do not have to restrict yourself to using a single family of
ResourceBundles. For example, you could have a set of bundles for
exception messages, ExceptionResources
(ExceptionResources_fr, ExceptionResources_de, ...),
and one for widgets, WidgetResource (WidgetResources_fr,
WidgetResources_de, ...); breaking up the resources however you like.
The equals method implements an equivalence relation
on non-null object references:
x, x.equals(x) should return
true.
x and y, x.equals(y)
should return true if and only if
y.equals(x) returns true.
x, y, and z, if
x.equals(y) returns true and
y.equals(z) returns true, then
x.equals(z) should return true.
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.
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.
getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader()),
except that getClassLoader() is run with the security
privileges of ResourceBundle.
See getBundle
for a complete description of the search and instantiation strategy.
getBundle(baseName, locale, this.getClass().getClassLoader()),
except that getClassLoader() is run with the security
privileges of ResourceBundle.
See getBundle
for a complete description of the search and instantiation strategy.
Conceptually, getBundle uses the following strategy for locating and instantiating
resource bundles:
getBundle uses the base name, the specified locale, and the default
locale (obtained from Locale.getDefault
)
to generate a sequence of candidate bundle names.
If the specified locale's language, country, and variant are all empty
strings, then the base name is the only candidate bundle name.
Otherwise, the following sequence is generated from the attribute
values of the specified locale (language1, country1, and variant1)
and of the default locale (language2, country2, and variant2):
Candidate bundle names where the final component is an empty string are omitted. For example, if country1 is an empty string, the second candidate bundle name is omitted.
getBundle then iterates over the candidate bundle names to find the first
one for which it can instantiate an actual resource bundle. For each candidate
bundle name, it attempts to create a resource bundle:
getBundle creates a new instance of this class and uses it as the result
resource bundle.
getBundle attempts to locate a property resource file.
It generates a path name from the candidate bundle name by replacing all "." characters
with "/" and appending the string ".properties".
It attempts to find a "resource" with this name using
ClassLoader.getResource
.
(Note that a "resource" in the sense of getResource has nothing to do with
the contents of a resource bundle, it is just a container of data, such as a file.)
If it finds a "resource", it attempts to create a new
PropertyResourceBundle
instance from its contents.
If successful, this instance becomes the result resource bundle.
If no result resource bundle has been found, a MissingResourceException
is thrown.
Once a result resource bundle has been found, its parent chain is instantiated.
getBundle iterates over the candidate bundle names that can be
obtained by successively removing variant, country, and language
(each time with the preceding "_") from the bundle name of the result resource bundle.
As above, candidate bundle names where the final component is an empty string are omitted.
With each of the candidate bundle names it attempts to instantiate a resource bundle, as
described above.
Whenever it succeeds, it calls the previously instantiated resource
bundle's setParent
method
with the new resource bundle, unless the previously instantiated resource
bundle already has a non-null parent.
Implementations of getBundle may cache instantiated resource bundles
and return the same resource bundle instance multiple times. They may also
vary the sequence in which resource bundles are instantiated as long as the
selection of the result resource bundle and its parent chain are compatible with
the description above.
The baseName argument should be a fully qualified class name. However, for
compatibility with earlier versions, Sun's Java 2 runtime environments do not verify this,
and so it is possible to access PropertyResourceBundles by specifying a
path name (using "/") instead of a fully qualified class name (using ".").
Example: The following class and property files are provided:
MyResources.class, MyResources_fr_CH.properties, MyResources_fr_CH.class,
MyResources_fr.properties, MyResources_en.properties, MyResources_es_ES.class.
The contents of all files are valid (that is, public non-abstract subclasses of ResourceBundle for
the ".class" files, syntactically correct ".properties" files).
The default locale is Locale("en", "GB").
Calling getBundle with the shown locale argument values instantiates
resource bundles from the following sources:
getObject method.
If still not successful, it throws a MissingResourceException.
(String) getObject
(key).
(String[]) getObject
(key).
java.util.Hashtable.
The general contract of hashCode is:
hashCode method on each of
the two objects must produce the same integer result.
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.)
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.
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.