Serializable
, Cloneable
, Map<Object,Object>
Provider
public class Properties extends Hashtable<Object,Object>
Properties
class represents a persistent set of
properties. The Properties
can be saved to a stream
or loaded from a stream. Each key and its corresponding value in
the property list is a string.
A property list can contain another property list as its "defaults"; this second property list is searched if the property key is not found in the original property list.
Because Properties
inherits from Hashtable
, the
put
and putAll
methods can be applied to a
Properties
object. Their use is strongly discouraged as they
allow the caller to insert entries whose keys or values are not
Strings
. The setProperty
method should be used
instead. If the store
or save
method is called
on a "compromised" Properties
object that contains a
non-String
key or value, the call will fail. Similarly,
the call to the propertyNames
or list
method
will fail if it is called on a "compromised" Properties
object that contains a non-String
key.
The iterators returned by the iterator
method of this class's
"collection views" (that is, entrySet()
, keySet()
, and
values()
) may not fail-fast (unlike the Hashtable implementation).
These iterators are guaranteed to traverse elements as they existed upon
construction exactly once, and may (but are not guaranteed to) reflect any
modifications subsequent to construction.
The load(Reader)
/
store(Writer, String)
methods load and store properties from and to a character based stream
in a simple line-oriented format specified below.
The load(InputStream)
/
store(OutputStream, String)
methods work the same way as the load(Reader)/store(Writer, String) pair, except
the input/output stream is encoded in ISO 8859-1 character encoding.
Characters that cannot be directly represented in this encoding can be written using
Unicode escapes as defined in section 3.3 of
The Java™ Language Specification;
only a single 'u' character is allowed in an escape
sequence.
The loadFromXML(InputStream)
and storeToXML(OutputStream, String, String)
methods load and store properties
in a simple XML format. By default the UTF-8 character encoding is used,
however a specific encoding may be specified if required. Implementations
are required to support UTF-8 and UTF-16 and may support other encodings.
An XML properties document has the following DOCTYPE declaration:
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">Note that the system URI (http://java.sun.com/dtd/properties.dtd) is not accessed when exporting or importing properties; it merely serves as a string to uniquely identify the DTD, which is:
<?xml version="1.0" encoding="UTF-8"?> <!-- DTD for properties --> <!ELEMENT properties ( comment?, entry* ) > <!ATTLIST properties version CDATA #FIXED "1.0"> <!ELEMENT comment (#PCDATA) > <!ELEMENT entry (#PCDATA) > <!ATTLIST entry key CDATA #REQUIRED>
This class is thread-safe: multiple threads can share a single
Properties
object without the need for external synchronization.
Modifier and Type | Field | Description |
---|---|---|
protected Properties |
defaults |
A property list that contains default values for any keys not
found in this property list.
|
Constructor | Description |
---|---|
Properties() |
Creates an empty property list with no default values.
|
Properties(Properties defaults) |
Creates an empty property list with the specified defaults.
|
Modifier and Type | Method | Description |
---|---|---|
void |
clear() |
Clears this hashtable so that it contains no keys.
|
Object |
clone() |
Creates a shallow copy of this hashtable.
|
Object |
compute(Object key,
BiFunction<? super Object,? super Object,?> remappingFunction) |
Attempts to compute a mapping for the specified key and its current
mapped value (or
null if there is no current mapping). |
Object |
computeIfAbsent(Object key,
Function<? super Object,?> mappingFunction) |
If the specified key is not already associated with a value (or is mapped
to
null ), attempts to compute its value using the given mapping
function and enters it into this map unless null . |
Object |
computeIfPresent(Object key,
BiFunction<? super Object,? super Object,?> remappingFunction) |
If the value for the specified key is present and non-null, attempts to
compute a new mapping given the key and its current mapped value.
|
boolean |
contains(Object value) |
Tests if some key maps into the specified value in this hashtable.
|
boolean |
containsKey(Object key) |
Tests if the specified object is a key in this hashtable.
|
boolean |
containsValue(Object value) |
Returns true if this hashtable maps one or more keys to this value.
|
Enumeration<Object> |
elements() |
Returns an enumeration of the values in this hashtable.
|
Set<Map.Entry<Object,Object>> |
entrySet() |
Returns a
Set view of the mappings contained in this map. |
boolean |
equals(Object o) |
Compares the specified Object with this Map for equality,
as per the definition in the Map interface.
|
void |
forEach(BiConsumer<? super Object,? super Object> action) |
Performs the given action for each entry in this map until all entries
have been processed or the action throws an exception.
|
Object |
get(Object key) |
Returns the value to which the specified key is mapped,
or
null if this map contains no mapping for the key. |
Object |
getOrDefault(Object key,
Object defaultValue) |
Returns the value to which the specified key is mapped, or
defaultValue if this map contains no mapping for the key. |
String |
getProperty(String key) |
Searches for the property with the specified key in this property list.
|
String |
getProperty(String key,
String defaultValue) |
Searches for the property with the specified key in this property list.
|
int |
hashCode() |
Returns the hash code value for this Map as per the definition in the
Map interface.
|
boolean |
isEmpty() |
Tests if this hashtable maps no keys to values.
|
Enumeration<Object> |
keys() |
Returns an enumeration of the keys in this hashtable.
|
Set<Object> |
keySet() |
Returns a
Set view of the keys contained in this map. |
void |
list(PrintStream out) |
Prints this property list out to the specified output stream.
|
void |
list(PrintWriter out) |
Prints this property list out to the specified output stream.
|
void |
load(InputStream inStream) |
Reads a property list (key and element pairs) from the input
byte stream.
|
void |
load(Reader reader) |
Reads a property list (key and element pairs) from the input
character stream in a simple line-oriented format.
|
void |
loadFromXML(InputStream in) |
Loads all of the properties represented by the XML document on the
specified input stream into this properties table.
|
Object |
merge(Object key,
Object value,
BiFunction<? super Object,? super Object,?> remappingFunction) |
If the specified key is not already associated with a value or is
associated with null, associates it with the given non-null value.
|
Enumeration<?> |
propertyNames() |
Returns an enumeration of all the keys in this property list,
including distinct keys in the default property list if a key
of the same name has not already been found from the main
properties list.
|
Object |
put(Object key,
Object value) |
Maps the specified
key to the specified
value in this hashtable. |
void |
putAll(Map<?,?> t) |
Copies all of the mappings from the specified map to this hashtable.
|
Object |
putIfAbsent(Object key,
Object value) |
If the specified key is not already associated with a value (or is mapped
to
null ) associates it with the given value and returns
null , else returns the current value. |
protected void |
rehash() |
Increases the capacity of and internally reorganizes this
hashtable, in order to accommodate and access its entries more
efficiently.
|
Object |
remove(Object key) |
Removes the key (and its corresponding value) from this
hashtable.
|
boolean |
remove(Object key,
Object value) |
Removes the entry for the specified key only if it is currently
mapped to the specified value.
|
Object |
replace(Object key,
Object value) |
Replaces the entry for the specified key only if it is
currently mapped to some value.
|
void |
replaceAll(BiFunction<? super Object,? super Object,?> function) |
Replaces each entry's value with the result of invoking the given
function on that entry until all entries have been processed or the
function throws an exception.
|
void |
save(OutputStream out,
String comments) |
Deprecated.
This method does not throw an IOException if an I/O error
occurs while saving the property list. The preferred way to save a
properties list is via the
store(OutputStream out,
String comments) method or the
storeToXML(OutputStream os, String comment) method. |
Object |
setProperty(String key,
String value) |
Calls the
Hashtable method put . |
int |
size() |
Returns the number of keys in this hashtable.
|
void |
store(OutputStream out,
String comments) |
Writes this property list (key and element pairs) in this
Properties table to the output stream in a format suitable
for loading into a Properties table using the
load(InputStream) method. |
void |
store(Writer writer,
String comments) |
Writes this property list (key and element pairs) in this
Properties table to the output character stream in a
format suitable for using the load(Reader)
method. |
void |
storeToXML(OutputStream os,
String comment) |
Emits an XML document representing all of the properties contained
in this table.
|
void |
storeToXML(OutputStream os,
String comment,
String encoding) |
Emits an XML document representing all of the properties contained
in this table, using the specified encoding.
|
Set<String> |
stringPropertyNames() |
Returns an unmodifiable set of keys from this property list
where the key and its corresponding value are strings,
including distinct keys in the default property list if a key
of the same name has not already been found from the main
properties list.
|
String |
toString() |
Returns a string representation of this
Hashtable object
in the form of a set of entries, enclosed in braces and separated
by the ASCII characters " , " (comma and space). |
Collection<Object> |
values() |
Returns a
Collection view of the values contained in this map. |
protected Properties defaults
public Properties()
public Properties(Properties defaults)
defaults
- the defaults.public Object setProperty(String key, String value)
Hashtable
method put
. Provided for
parallelism with the getProperty
method. Enforces use of
strings for property keys and values. The value returned is the
result of the Hashtable
call to put
.key
- the key to be placed into this property list.value
- the value corresponding to key
.null
if it did not have one.getProperty(java.lang.String)
public void load(Reader reader) throws IOException
Properties are processed in terms of lines. There are two
kinds of line, natural lines and logical lines.
A natural line is defined as a line of
characters that is terminated either by a set of line terminator
characters (\n
or \r
or \r\n
)
or by the end of the stream. A natural line may be either a blank line,
a comment line, or hold all or some of a key-element pair. A logical
line holds all the data of a key-element pair, which may be spread
out across several adjacent natural lines by escaping
the line terminator sequence with a backslash character
\
. Note that a comment line cannot be extended
in this manner; every natural line that is a comment must have
its own comment indicator, as described below. Lines are read from
input until the end of the stream is reached.
A natural line that contains only white space characters is
considered blank and is ignored. A comment line has an ASCII
'#'
or '!'
as its first non-white
space character; comment lines are also ignored and do not
encode key-element information. In addition to line
terminators, this format considers the characters space
(' '
, '\u0020'
), tab
('\t'
, '\u0009'
), and form feed
('\f'
, '\u000C'
) to be white
space.
If a logical line is spread across several natural lines, the backslash escaping the line terminator sequence, the line terminator sequence, and any white space at the start of the following line have no affect on the key or element values. The remainder of the discussion of key and element parsing (when loading) will assume all the characters constituting the key and element appear on a single natural line after line continuation characters have been removed. Note that it is not sufficient to only examine the character preceding a line terminator sequence to decide if the line terminator is escaped; there must be an odd number of contiguous backslashes for the line terminator to be escaped. Since the input is processed from left to right, a non-zero even number of 2n contiguous backslashes before a line terminator (or elsewhere) encodes n backslashes after escape processing.
The key contains all of the characters in the line starting
with the first non-white space character and up to, but not
including, the first unescaped '='
,
':'
, or white space character other than a line
terminator. All of these key termination characters may be
included in the key by escaping them with a preceding backslash
character; for example,
\:\=
would be the two-character key ":="
. Line
terminator characters can be included using \r
and
\n
escape sequences. Any white space after the
key is skipped; if the first non-white space character after
the key is '='
or ':'
, then it is
ignored and any white space characters after it are also
skipped. All remaining characters on the line become part of
the associated element string; if there are no remaining
characters, the element is the empty string
""
. Once the raw character sequences
constituting the key and element are identified, escape
processing is performed as described above.
As an example, each of the following three lines specifies the key
"Truth"
and the associated element value
"Beauty"
:
Truth = Beauty Truth:Beauty Truth :BeautyAs another example, the following three lines specify a single property:
fruits apple, banana, pear, \ * cantaloupe, watermelon, \ * kiwi, mangoThe key is
"fruits"
and the associated element is:
"apple, banana, pear, cantaloupe, watermelon, kiwi, mango"Note that a space appears before each
\
so that a space
will appear after each comma in the final result; the \
,
line terminator, and leading white space on the continuation line are
merely discarded and are not replaced by one or more other
characters.
As a third example, the line:
cheesesspecifies that the key is
"cheeses"
and the associated
element is the empty string ""
.
Characters in keys and elements can be represented in escape sequences similar to those used for character and string literals (see sections 3.3 and 3.10.6 of The Java™ Language Specification). The differences from the character escape sequences and Unicode escapes used for characters and strings are:
\b
does not
represent a backspace character.
\
, before a non-valid escape character as an
error; the backslash is silently dropped. For example, in a
Java string the sequence "\z"
would cause a
compile time error. In contrast, this method silently drops
the backslash. Therefore, this method treats the two character
sequence "\b"
as equivalent to the single
character 'b'
.
The specified stream remains open after this method returns.
reader
- the input character stream.IOException
- if an error occurred when reading from the
input stream.IllegalArgumentException
- if a malformed Unicode escape
appears in the input.NullPointerException
- if reader
is null.public void load(InputStream inStream) throws IOException
load(Reader)
and is assumed to use
the ISO 8859-1 character encoding; that is each byte is one Latin1
character. Characters not in Latin1, and certain special characters,
are represented in keys and elements using Unicode escapes as defined in
section 3.3 of
The Java™ Language Specification.
The specified stream remains open after this method returns.
inStream
- the input stream.IOException
- if an error occurred when reading from the
input stream.IllegalArgumentException
- if the input stream contains a
malformed Unicode escape sequence.NullPointerException
- if inStream
is null.@Deprecated public void save(OutputStream out, String comments)
store(OutputStream out,
String comments)
method or the
storeToXML(OutputStream os, String comment)
method.store(OutputStream out, String comments)
method
and suppresses IOExceptions that were thrown.out
- an output stream.comments
- a description of the property list.ClassCastException
- if this Properties
object
contains any keys or values that are not
Strings
.public void store(Writer writer, String comments) throws IOException
Properties
table to the output character stream in a
format suitable for using the load(Reader)
method.
Properties from the defaults table of this Properties
table (if any) are not written out by this method.
If the comments argument is not null, then an ASCII #
character, the comments string, and a line separator are first written
to the output stream. Thus, the comments
can serve as an
identifying comment. Any one of a line feed ('\n'), a carriage
return ('\r'), or a carriage return followed immediately by a line feed
in comments is replaced by a line separator generated by the Writer
and if the next character in comments is not character #
or
character !
then an ASCII #
is written out
after that line separator.
Next, a comment line is always written, consisting of an ASCII
#
character, the current date and time (as if produced
by the toString
method of Date
for the
current time), and a line separator as generated by the Writer
.
Then every entry in this Properties
table is
written out, one per line. For each entry the key string is
written, then an ASCII =
, then the associated
element string. For the key, all space characters are
written with a preceding \
character. For the
element, leading space characters, but not embedded or trailing
space characters, are written with a preceding \
character. The key and element characters #
,
!
, =
, and :
are written
with a preceding backslash to ensure that they are properly loaded.
After the entries have been written, the output stream is flushed. The output stream remains open after this method returns.
writer
- an output character stream writer.comments
- a description of the property list.IOException
- if writing this property list to the specified
output stream throws an IOException
.ClassCastException
- if this Properties
object
contains any keys or values that are not Strings
.NullPointerException
- if writer
is null.public void store(OutputStream out, String comments) throws IOException
Properties
table to the output stream in a format suitable
for loading into a Properties
table using the
load(InputStream)
method.
Properties from the defaults table of this Properties
table (if any) are not written out by this method.
This method outputs the comments, properties keys and values in
the same format as specified in
store(Writer)
,
with the following differences:
\u
xxxx for their appropriate unicode
hexadecimal value xxxx.
\u0020
and characters greater
than \u007E
in property keys or values are written
as \u
xxxx for the appropriate hexadecimal
value xxxx.
After the entries have been written, the output stream is flushed. The output stream remains open after this method returns.
out
- an output stream.comments
- a description of the property list.IOException
- if writing this property list to the specified
output stream throws an IOException
.ClassCastException
- if this Properties
object
contains any keys or values that are not Strings
.NullPointerException
- if out
is null.public void loadFromXML(InputStream in) throws IOException, InvalidPropertiesFormatException
The XML document must have the following DOCTYPE declaration:
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">Furthermore, the document must satisfy the properties DTD described above.
An implementation is required to read XML documents that use the
"UTF-8
" or "UTF-16
" encoding. An implementation may
support additional encodings.
The specified stream is closed after this method returns.
in
- the input stream from which to read the XML document.IOException
- if reading from the specified input stream
results in an IOException
.UnsupportedEncodingException
- if the document's encoding
declaration can be read and it specifies an encoding that is not
supportedInvalidPropertiesFormatException
- Data on input stream does not
constitute a valid XML document with the mandated document type.NullPointerException
- if in
is null.storeToXML(OutputStream, String, String)
,
Character
Encoding in Entitiespublic void storeToXML(OutputStream os, String comment) throws IOException
An invocation of this method of the form props.storeToXML(os,
comment)
behaves in exactly the same way as the invocation
props.storeToXML(os, comment, "UTF-8");
.
os
- the output stream on which to emit the XML document.comment
- a description of the property list, or null
if no comment is desired.IOException
- if writing to the specified output stream
results in an IOException
.NullPointerException
- if os
is null.ClassCastException
- if this Properties
object
contains any keys or values that are not
Strings
.loadFromXML(InputStream)
public void storeToXML(OutputStream os, String comment, String encoding) throws IOException
The XML document will have the following DOCTYPE declaration:
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
If the specified comment is null
then no comment
will be stored in the document.
An implementation is required to support writing of XML documents
that use the "UTF-8
" or "UTF-16
" encoding. An
implementation may support additional encodings.
The specified stream remains open after this method returns.
os
- the output stream on which to emit the XML document.comment
- a description of the property list, or null
if no comment is desired.encoding
- the name of a supported
character encodingIOException
- if writing to the specified output stream
results in an IOException
.UnsupportedEncodingException
- if the encoding is not
supported by the implementation.NullPointerException
- if os
is null
,
or if encoding
is null
.ClassCastException
- if this Properties
object
contains any keys or values that are not
Strings
.loadFromXML(InputStream)
,
Character
Encoding in Entitiespublic String getProperty(String key)
null
if the property is not found.key
- the property key.setProperty(java.lang.String, java.lang.String)
,
defaults
public String getProperty(String key, String defaultValue)
key
- the hashtable key.defaultValue
- a default value.setProperty(java.lang.String, java.lang.String)
,
defaults
public Enumeration<?> propertyNames()
ClassCastException
- if any key in this property list
is not a string.Enumeration
,
defaults
,
stringPropertyNames()
public Set<String> stringPropertyNames()
String
are omitted.
The returned set is not backed by this Properties
object.
Changes to this Properties
object are not reflected in the
returned set.
defaults
public void list(PrintStream out)
out
- an output stream.ClassCastException
- if any key in this property list
is not a string.public void list(PrintWriter out)
out
- an output stream.ClassCastException
- if any key in this property list
is not a string.public int size()
Hashtable
public boolean isEmpty()
Hashtable
public Enumeration<Object> keys()
Hashtable
keys
in class Hashtable<Object,Object>
Enumeration
,
Hashtable.elements()
,
Hashtable.keySet()
,
Map
public Enumeration<Object> elements()
Hashtable
elements
in class Hashtable<Object,Object>
Enumeration
,
Hashtable.keys()
,
Hashtable.values()
,
Map
public boolean contains(Object value)
Hashtable
containsKey
method.
Note that this method is identical in functionality to
containsValue
, (which is part of the
Map
interface in the collections framework).
public boolean containsValue(Object value)
Hashtable
Note that this method is identical in functionality to contains
(which predates the Map
interface).
containsValue
in interface Map<Object,Object>
containsValue
in class Hashtable<Object,Object>
value
- value whose presence in this hashtable is to be testedtrue
if this map maps one or more keys to the
specified valuepublic boolean containsKey(Object key)
Hashtable
containsKey
in interface Map<Object,Object>
containsKey
in class Hashtable<Object,Object>
key
- possible keytrue
if and only if the specified object
is a key in this hashtable, as determined by the
equals
method; false
otherwise.Hashtable.contains(Object)
public Object get(Object key)
Hashtable
null
if this map contains no mapping for the key.
More formally, if this map contains a mapping from a key
k
to a value v
such that (key.equals(k))
,
then this method returns v
; otherwise it returns
null
. (There can be at most one such mapping.)
get
in interface Map<Object,Object>
get
in class Hashtable<Object,Object>
key
- the key whose associated value is to be returnednull
if this map contains no mapping for the keyHashtable.put(Object, Object)
public Object put(Object key, Object value)
Hashtable
key
to the specified
value
in this hashtable. Neither the key nor the
value can be null
.
The value can be retrieved by calling the get
method
with a key that is equal to the original key.
put
in interface Map<Object,Object>
put
in class Hashtable<Object,Object>
key
- the hashtable keyvalue
- the valuenull
if it did not have oneObject.equals(Object)
,
Hashtable.get(Object)
public Object remove(Object key)
Hashtable
public void putAll(Map<?,?> t)
Hashtable
public void clear()
Hashtable
public String toString()
Hashtable
Hashtable
object
in the form of a set of entries, enclosed in braces and separated
by the ASCII characters " ,
" (comma and space). Each
entry is rendered as the key, an equals sign =
, and the
associated element, where the toString
method is used to
convert the key and element to strings.public Set<Object> keySet()
Hashtable
Set
view of the keys contained in this map.
The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own remove
operation), the results of
the iteration are undefined. The set supports element removal,
which removes the corresponding mapping from the map, via the
Iterator.remove
, Set.remove
,
removeAll
, retainAll
, and clear
operations. It does not support the add
or addAll
operations.public Collection<Object> values()
Hashtable
Collection
view of the values contained in this map.
The collection is backed by the map, so changes to the map are
reflected in the collection, and vice-versa. If the map is
modified while an iteration over the collection is in progress
(except through the iterator's own remove
operation),
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove
,
Collection.remove
, removeAll
,
retainAll
and clear
operations. It does not
support the add
or addAll
operations.public Set<Map.Entry<Object,Object>> entrySet()
Hashtable
Set
view of the mappings contained in this map.
The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own remove
operation, or through the
setValue
operation on a map entry returned by the
iterator) the results of the iteration are undefined. The set
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove
,
Set.remove
, removeAll
, retainAll
and
clear
operations. It does not support the
add
or addAll
operations.public boolean equals(Object o)
Hashtable
public int hashCode()
Hashtable
public Object getOrDefault(Object key, Object defaultValue)
Map
defaultValue
if this map contains no mapping for the key.getOrDefault
in interface Map<Object,Object>
getOrDefault
in class Hashtable<Object,Object>
key
- the key whose associated value is to be returneddefaultValue
- the default mapping of the keydefaultValue
if this map contains no mapping for the keypublic void forEach(BiConsumer<? super Object,? super Object> action)
Map
public void replaceAll(BiFunction<? super Object,? super Object,?> function)
Map
replaceAll
in interface Map<Object,Object>
replaceAll
in class Hashtable<Object,Object>
function
- the function to apply to each entrypublic Object putIfAbsent(Object key, Object value)
Map
null
) associates it with the given value and returns
null
, else returns the current value.putIfAbsent
in interface Map<Object,Object>
putIfAbsent
in class Hashtable<Object,Object>
key
- key with which the specified value is to be associatedvalue
- value to be associated with the specified keynull
if there was no mapping for the key.
(A null
return can also indicate that the map
previously associated null
with the key,
if the implementation supports null values.)public boolean remove(Object key, Object value)
Map
public Object replace(Object key, Object value)
Map
replace
in interface Map<Object,Object>
replace
in class Hashtable<Object,Object>
key
- key with which the specified value is associatedvalue
- value to be associated with the specified keynull
if there was no mapping for the key.
(A null
return can also indicate that the map
previously associated null
with the key,
if the implementation supports null values.)public Object computeIfAbsent(Object key, Function<? super Object,?> mappingFunction)
Hashtable
null
), attempts to compute its value using the given mapping
function and enters it into this map unless null
.
If the mapping function returns null
, no mapping is recorded.
If the mapping function itself throws an (unchecked) exception, the
exception is rethrown, and no mapping is recorded. The most
common usage is to construct a new object serving as an initial
mapped value or memoized result, as in:
map.computeIfAbsent(key, k -> new Value(f(k)));
Or to implement a multi-value map, Map<K,Collection<V>>
,
supporting multiple values per key:
map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
The mapping function should not modify this map during computation.
This method will, on a best-effort basis, throw a
ConcurrentModificationException
if the mapping
function modified this map during computation.
computeIfAbsent
in interface Map<Object,Object>
computeIfAbsent
in class Hashtable<Object,Object>
key
- key with which the specified value is to be associatedmappingFunction
- the mapping function to compute a valuepublic Object computeIfPresent(Object key, BiFunction<? super Object,? super Object,?> remappingFunction)
Hashtable
If the remapping function returns null
, the mapping is removed.
If the remapping function itself throws an (unchecked) exception, the
exception is rethrown, and the current mapping is left unchanged.
The remapping function should not modify this map during computation.
This method will, on a best-effort basis, throw a
ConcurrentModificationException
if the remapping
function modified this map during computation.
computeIfPresent
in interface Map<Object,Object>
computeIfPresent
in class Hashtable<Object,Object>
key
- key with which the specified value is to be associatedremappingFunction
- the remapping function to compute a valuepublic Object compute(Object key, BiFunction<? super Object,? super Object,?> remappingFunction)
Hashtable
null
if there is no current mapping). For
example, to either create or append a String
msg to a value
mapping:
map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))
(Method merge()
is often simpler to use for such purposes.)
If the remapping function returns null
, the mapping is removed
(or remains absent if initially absent). If the remapping function
itself throws an (unchecked) exception, the exception is rethrown, and
the current mapping is left unchanged.
The remapping function should not modify this map during computation.
This method will, on a best-effort basis, throw a
ConcurrentModificationException
if the remapping
function modified this map during computation.
compute
in interface Map<Object,Object>
compute
in class Hashtable<Object,Object>
key
- key with which the specified value is to be associatedremappingFunction
- the remapping function to compute a valuepublic Object merge(Object key, Object value, BiFunction<? super Object,? super Object,?> remappingFunction)
Hashtable
null
. This
method may be of use when combining multiple mapped values for a key.
For example, to either create or append a String msg
to a
value mapping:
map.merge(key, msg, String::concat)
If the remapping function returns null
, the mapping is removed.
If the remapping function itself throws an (unchecked) exception, the
exception is rethrown, and the current mapping is left unchanged.
The remapping function should not modify this map during computation.
This method will, on a best-effort basis, throw a
ConcurrentModificationException
if the remapping
function modified this map during computation.
merge
in interface Map<Object,Object>
merge
in class Hashtable<Object,Object>
key
- key with which the resulting value is to be associatedvalue
- the non-null value to be merged with the existing value
associated with the key or, if no existing value or a null value
is associated with the key, to be associated with the keyremappingFunction
- the remapping function to recompute a value if
presentprotected void rehash()
Hashtable
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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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DRAFT 9-internal+0-adhoc.mlchung.jdk9-jdeps