Module java.base
Package java.util

Class Properties

  • All Implemented Interfaces:
    Serializable, Cloneable, Map<Object,Object>
    Direct Known Subclasses:
    Provider

    public class Properties
extends Hashtable<Object,Object>
    The 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.

    Since:
    1.0
    See Also:
    Serialized Form

    • Field Summary

      Fields 
      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 Summary

      Constructors 
      Constructor Description
      Properties​()
      Creates an empty property list with no default values.
      Properties​(Properties defaults)
      Creates an empty property list with the specified defaults.

    • Method Summary

      All Methods Instance Methods Concrete Methods Deprecated Methods 
      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.

    • Field Detail

      • defaults

        protected Properties defaults
        A property list that contains default values for any keys not found in this property list.

    • Constructor Detail

      • Properties

        public Properties​()
        Creates an empty property list with no default values.

      • Properties

        public Properties​(Properties defaults)
        Creates an empty property list with the specified defaults.
        Parameters:
        defaults - the defaults.

    • Method Detail

      • setProperty

        public Object setProperty​(String key,
                          String value)
        Calls the 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.
        Parameters:
        key - the key to be placed into this property list.
        value - the value corresponding to key.
        Returns:
        the previous value of the specified key in this property list, or null if it did not have one.
        Since:
        1.2
        See Also:
        getProperty(java.lang.String)

      • load

        public void load​(Reader reader)
          throws IOException
        Reads a property list (key and element pairs) from the input character stream in a simple line-oriented format.

        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                    :Beauty
        As another example, the following three lines specify a single property: 
         fruits                           apple, banana, pear, \
     *                                  cantaloupe, watermelon, \
     *                                  kiwi, mango
        The 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: 

        cheeses
        specifies 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:

        • Octal escapes are not recognized.
        • The character sequence \b does not represent a backspace character.
        • The method does not treat a backslash 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'.
        • Escapes are not necessary for single and double quotes; however, by the rule above, single and double quote characters preceded by a backslash still yield single and double quote characters, respectively.
        • Only a single 'u' character is allowed in a Unicode escape sequence.

        The specified stream remains open after this method returns.

        Parameters:
        reader - the input character stream.
        Throws:
        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.
        Since:
        1.6

      • load

        public void load​(InputStream inStream)
          throws IOException
        Reads a property list (key and element pairs) from the input byte stream. The input stream is in a simple line-oriented format as specified in 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.

        Parameters:
        inStream - the input stream.
        Throws:
        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.
        Since:
        1.2

      • save

        @Deprecated
public 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.
        Calls the store(OutputStream out, String comments) method and suppresses IOExceptions that were thrown.
        Parameters:
        out - an output stream.
        comments - a description of the property list.
        Throws:
        ClassCastException - if this Properties object contains any keys or values that are not Strings.

      • store

        public void store​(Writer writer,
                  String comments)
           throws IOException
        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.

        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.

        Parameters:
        writer - an output character stream writer.
        comments - a description of the property list.
        Throws:
        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.
        Since:
        1.6

      • store

        public void store​(OutputStream out,
                  String comments)
           throws IOException
        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.

        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:

        • The stream is written using the ISO 8859-1 character encoding.
        • Characters not in Latin-1 in the comments are written as \uxxxx for their appropriate unicode hexadecimal value xxxx.
        • Characters less than \u0020 and characters greater than \u007E in property keys or values are written as \uxxxx 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.

        Parameters:
        out - an output stream.
        comments - a description of the property list.
        Throws:
        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.
        Since:
        1.2

      • loadFromXML

        public void loadFromXML​(InputStream in)
                 throws IOException,
                        InvalidPropertiesFormatException
        Loads all of the properties represented by the XML document on the specified input stream into this properties table.

        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.

        Parameters:
        in - the input stream from which to read the XML document.
        Throws:
        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 supported
        InvalidPropertiesFormatException - Data on input stream does not constitute a valid XML document with the mandated document type.
        NullPointerException - if in is null.
        Since:
        1.5
        See Also:
        storeToXML(OutputStream, String, String), Character Encoding in Entities

      • storeToXML

        public void storeToXML​(OutputStream os,
                       String comment)
                throws IOException
        Emits an XML document representing all of the properties contained in this table.

        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");.

        Parameters:
        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.
        Throws:
        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.
        Since:
        1.5
        See Also:
        loadFromXML(InputStream)

      • storeToXML

        public void storeToXML​(OutputStream os,
                       String comment,
                       String encoding)
                throws IOException
        Emits an XML document representing all of the properties contained in this table, using the specified encoding.

        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.

        Parameters:
        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 encoding
        Throws:
        IOException - 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.
        Since:
        1.5
        See Also:
        loadFromXML(InputStream), Character Encoding in Entities

      • getProperty

        public String getProperty​(String key)
        Searches for the property with the specified key in this property list. If the key is not found in this property list, the default property list, and its defaults, recursively, are then checked. The method returns null if the property is not found.
        Parameters:
        key - the property key.
        Returns:
        the value in this property list with the specified key value.
        See Also:
        setProperty(java.lang.String, java.lang.String), defaults

      • getProperty

        public String getProperty​(String key,
                          String defaultValue)
        Searches for the property with the specified key in this property list. If the key is not found in this property list, the default property list, and its defaults, recursively, are then checked. The method returns the default value argument if the property is not found.
        Parameters:
        key - the hashtable key.
        defaultValue - a default value.
        Returns:
        the value in this property list with the specified key value.
        See Also:
        setProperty(java.lang.String, java.lang.String), defaults

      • propertyNames

        public 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.
        Returns:
        an enumeration of all the keys in this property list, including the keys in the default property list.
        Throws:
        ClassCastException - if any key in this property list is not a string.
        See Also:
        Enumeration, defaults, stringPropertyNames()

      • stringPropertyNames

        public 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. Properties whose key or value is not of type 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.

        Returns:
        an unmodifiable set of keys in this property list where the key and its corresponding value are strings, including the keys in the default property list.
        Since:
        1.6
        See Also:
        defaults

      • list

        public void list​(PrintStream out)
        Prints this property list out to the specified output stream. This method is useful for debugging.
        Parameters:
        out - an output stream.
        Throws:
        ClassCastException - if any key in this property list is not a string.

      • list

        public void list​(PrintWriter out)
        Prints this property list out to the specified output stream. This method is useful for debugging.
        Parameters:
        out - an output stream.
        Throws:
        ClassCastException - if any key in this property list is not a string.
        Since:
        1.1

      • size

        public int size​()
        Description copied from class: Hashtable
        Returns the number of keys in this hashtable.
        Specified by:
        size in interface Map<Object,Object>
        Overrides:
        size in class Hashtable<Object,Object>
        Returns:
        the number of keys in this hashtable.

      • isEmpty

        public boolean isEmpty​()
        Description copied from class: Hashtable
        Tests if this hashtable maps no keys to values.
        Specified by:
        isEmpty in interface Map<Object,Object>
        Overrides:
        isEmpty in class Hashtable<Object,Object>
        Returns:
        true if this hashtable maps no keys to values; false otherwise.

      • keys

        public Enumeration<Object> keys​()
        Description copied from class: Hashtable
        Returns an enumeration of the keys in this hashtable. Use the Enumeration methods on the returned object to fetch the keys sequentially. If the hashtable is structurally modified while enumerating over the keys then the results of enumerating are undefined.
        Overrides:
        keys in class Hashtable<Object,Object>
        Returns:
        an enumeration of the keys in this hashtable.
        See Also:
        Enumeration, Hashtable.elements(), Hashtable.keySet(), Map

      • elements

        public Enumeration<Object> elements​()
        Description copied from class: Hashtable
        Returns an enumeration of the values in this hashtable. Use the Enumeration methods on the returned object to fetch the elements sequentially. If the hashtable is structurally modified while enumerating over the values then the results of enumerating are undefined.
        Overrides:
        elements in class Hashtable<Object,Object>
        Returns:
        an enumeration of the values in this hashtable.
        See Also:
        Enumeration, Hashtable.keys(), Hashtable.values(), Map

      • contains

        public boolean contains​(Object value)
        Description copied from class: Hashtable
        Tests if some key maps into the specified value in this hashtable. This operation is more expensive than the containsKey method.

        Note that this method is identical in functionality to containsValue, (which is part of the Map interface in the collections framework).

        Overrides:
        contains in class Hashtable<Object,Object>
        Parameters:
        value - a value to search for
        Returns:
        true if and only if some key maps to the value argument in this hashtable as determined by the equals method; false otherwise.

      • containsValue

        public boolean containsValue​(Object value)
        Description copied from class: Hashtable
        Returns true if this hashtable maps one or more keys to this value.

        Note that this method is identical in functionality to contains (which predates the Map interface).

        Specified by:
        containsValue in interface Map<Object,Object>
        Overrides:
        containsValue in class Hashtable<Object,Object>
        Parameters:
        value - value whose presence in this hashtable is to be tested
        Returns:
        true if this map maps one or more keys to the specified value

      • get

        public Object get​(Object key)
        Description copied from class: Hashtable
        Returns the value to which the specified key is mapped, or 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.)

        Specified by:
        get in interface Map<Object,Object>
        Overrides:
        get in class Hashtable<Object,Object>
        Parameters:
        key - the key whose associated value is to be returned
        Returns:
        the value to which the specified key is mapped, or null if this map contains no mapping for the key
        See Also:
        Hashtable.put(Object, Object)

      • put

        public Object put​(Object key,
                  Object value)
        Description copied from class: Hashtable
        Maps the specified 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.

        Specified by:
        put in interface Map<Object,Object>
        Overrides:
        put in class Hashtable<Object,Object>
        Parameters:
        key - the hashtable key
        value - the value
        Returns:
        the previous value of the specified key in this hashtable, or null if it did not have one
        See Also:
        Object.equals(Object), Hashtable.get(Object)

      • remove

        public Object remove​(Object key)
        Description copied from class: Hashtable
        Removes the key (and its corresponding value) from this hashtable. This method does nothing if the key is not in the hashtable.
        Specified by:
        remove in interface Map<Object,Object>
        Overrides:
        remove in class Hashtable<Object,Object>
        Parameters:
        key - the key that needs to be removed
        Returns:
        the value to which the key had been mapped in this hashtable, or null if the key did not have a mapping

      • putAll

        public void putAll​(Map<?,?> t)
        Description copied from class: Hashtable
        Copies all of the mappings from the specified map to this hashtable. These mappings will replace any mappings that this hashtable had for any of the keys currently in the specified map.
        Specified by:
        putAll in interface Map<Object,Object>
        Overrides:
        putAll in class Hashtable<Object,Object>
        Parameters:
        t - mappings to be stored in this map

      • toString

        public String toString​()
        Description copied from class: Hashtable
        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). 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.
        Overrides:
        toString in class Hashtable<Object,Object>
        Returns:
        a string representation of this hashtable

      • keySet

        public Set<Object> keySet​()
        Description copied from class: Hashtable
        Returns a 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.
        Specified by:
        keySet in interface Map<Object,Object>
        Overrides:
        keySet in class Hashtable<Object,Object>
        Returns:
        a set view of the keys contained in this map

      • values

        public Collection<Object> values​()
        Description copied from class: Hashtable
        Returns a 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.
        Specified by:
        values in interface Map<Object,Object>
        Overrides:
        values in class Hashtable<Object,Object>
        Returns:
        a collection view of the values contained in this map

      • entrySet

        public Set<Map.Entry<Object,Object>> entrySet​()
        Description copied from class: Hashtable
        Returns a 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.
        Specified by:
        entrySet in interface Map<Object,Object>
        Overrides:
        entrySet in class Hashtable<Object,Object>
        Returns:
        a set view of the mappings contained in this map

      • equals

        public boolean equals​(Object o)
        Description copied from class: Hashtable
        Compares the specified Object with this Map for equality, as per the definition in the Map interface.
        Specified by:
        equals in interface Map<Object,Object>
        Overrides:
        equals in class Hashtable<Object,Object>
        Parameters:
        o - object to be compared for equality with this hashtable
        Returns:
        true if the specified Object is equal to this Map
        See Also:
        Map.equals(Object)

      • getOrDefault

        public Object getOrDefault​(Object key,
                           Object defaultValue)
        Description copied from interface: Map
        Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.
        Specified by:
        getOrDefault in interface Map<Object,Object>
        Overrides:
        getOrDefault in class Hashtable<Object,Object>
        Parameters:
        key - the key whose associated value is to be returned
        defaultValue - the default mapping of the key
        Returns:
        the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key

      • forEach

        public void forEach​(BiConsumer<? super Object,? super Object> action)
        Description copied from interface: Map
        Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of entry set iteration (if an iteration order is specified.) Exceptions thrown by the action are relayed to the caller.
        Specified by:
        forEach in interface Map<Object,Object>
        Overrides:
        forEach in class Hashtable<Object,Object>
        Parameters:
        action - The action to be performed for each entry

      • replaceAll

        public void replaceAll​(BiFunction<? super Object,? super Object,?> function)
        Description copied from interface: Map
        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. Exceptions thrown by the function are relayed to the caller.
        Specified by:
        replaceAll in interface Map<Object,Object>
        Overrides:
        replaceAll in class Hashtable<Object,Object>
        Parameters:
        function - the function to apply to each entry

      • putIfAbsent

        public Object putIfAbsent​(Object key,
                          Object value)
        Description copied from interface: Map
        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.
        Specified by:
        putIfAbsent in interface Map<Object,Object>
        Overrides:
        putIfAbsent in class Hashtable<Object,Object>
        Parameters:
        key - key with which the specified value is to be associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with the specified key, or null 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.)

      • remove

        public boolean remove​(Object key,
                      Object value)
        Description copied from interface: Map
        Removes the entry for the specified key only if it is currently mapped to the specified value.
        Specified by:
        remove in interface Map<Object,Object>
        Overrides:
        remove in class Hashtable<Object,Object>
        Parameters:
        key - key with which the specified value is associated
        value - value expected to be associated with the specified key
        Returns:
        true if the value was removed

      • replace

        public Object replace​(Object key,
                      Object value)
        Description copied from interface: Map
        Replaces the entry for the specified key only if it is currently mapped to some value.
        Specified by:
        replace in interface Map<Object,Object>
        Overrides:
        replace in class Hashtable<Object,Object>
        Parameters:
        key - key with which the specified value is associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with the specified key, or null 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.)

      • computeIfAbsent

        public Object computeIfAbsent​(Object key,
                              Function<? super Object,?> mappingFunction)
        Description copied from class: Hashtable
        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.

        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.

        Specified by:
        computeIfAbsent in interface Map<Object,Object>
        Overrides:
        computeIfAbsent in class Hashtable<Object,Object>
        Parameters:
        key - key with which the specified value is to be associated
        mappingFunction - the mapping function to compute a value
        Returns:
        the current (existing or computed) value associated with the specified key, or null if the computed value is null

      • computeIfPresent

        public Object computeIfPresent​(Object key,
                               BiFunction<? super Object,? super Object,?> remappingFunction)
        Description copied from class: Hashtable
        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.

        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.

        Specified by:
        computeIfPresent in interface Map<Object,Object>
        Overrides:
        computeIfPresent in class Hashtable<Object,Object>
        Parameters:
        key - key with which the specified value is to be associated
        remappingFunction - the remapping function to compute a value
        Returns:
        the new value associated with the specified key, or null if none

      • compute

        public Object compute​(Object key,
                      BiFunction<? super Object,? super Object,?> remappingFunction)
        Description copied from class: Hashtable
        Attempts to compute a mapping for the specified key and its current mapped value (or 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.

        Specified by:
        compute in interface Map<Object,Object>
        Overrides:
        compute in class Hashtable<Object,Object>
        Parameters:
        key - key with which the specified value is to be associated
        remappingFunction - the remapping function to compute a value
        Returns:
        the new value associated with the specified key, or null if none

      • merge

        public Object merge​(Object key,
                    Object value,
                    BiFunction<? super Object,? super Object,?> remappingFunction)
        Description copied from class: Hashtable
        If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value. Otherwise, replaces the associated value with the results of the given remapping function, or removes if the result is 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.

        Specified by:
        merge in interface Map<Object,Object>
        Overrides:
        merge in class Hashtable<Object,Object>
        Parameters:
        key - key with which the resulting value is to be associated
        value - 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 key
        remappingFunction - the remapping function to recompute a value if present
        Returns:
        the new value associated with the specified key, or null if no value is associated with the key

      • rehash

        protected void rehash​()
        Description copied from class: Hashtable
        Increases the capacity of and internally reorganizes this hashtable, in order to accommodate and access its entries more efficiently. This method is called automatically when the number of keys in the hashtable exceeds this hashtable's capacity and load factor.
        Overrides:
        rehash in class Hashtable<Object,Object>

      • clone

        public Object clone​()
        Description copied from class: Hashtable
        Creates a shallow copy of this hashtable. All the structure of the hashtable itself is copied, but the keys and values are not cloned. This is a relatively expensive operation.
        Overrides:
        clone in class Hashtable<Object,Object>
        Returns:
        a clone of the hashtable
        See Also:
        Cloneable