How to use SortedMap interface in Java

Question

I have a   Map lt Float  MyObject gt    What is the best way to keep the map sorted according to the float   Is SortedMap the best answer  TreeMap  How do I use it   I only create the map once and replace the MyObject frequently using myMap put   and myMap get

User · Answer

A TreeMap is probably the most straightforward way of doing this. You use it exactly like a normal Map. i.e.

Map<Float,String> mySortedMap = new TreeMap<Float,MyObject>();
// Put some values in it
mySortedMap.put(1.0f,"One");
mySortedMap.put(0.0f,"Zero");
mySortedMap.put(3.0f,"Three");

// Iterate through it and it'll be in order!
for(Map.Entry<Float,String> entry : mySortedMap.entrySet()) {
    System.out.println(entry.getValue());
} // outputs Zero One Three

It's worth taking a look at the API docs, http://download.oracle.com/javase/6/docs/api/java/util/TreeMap.html to see what else you can do with it.

User · Answer

TreeMap  which is an implementation of the SortedMap interface  would work      How do I use it      Map lt Float  MyObject gt  map   new TreeMap lt Float  MyObject gt

User · Answer

I would use TreeMap  which implements SortedMap  It is designed exactly for that   Example   Map lt Integer  String gt  map   new TreeMap lt Integer  String gt         Add Items to the TreeMap map put 1   One    map put 2   Two    map put 3   Three        Iterate over them for  Map Entry lt Integer  String gt  entry   map entrySet          System out println entry getKey         gt      entry getValue         See the Java tutorial page for SortedMap  And here a list of tutorials related to TreeMap

User · Answer

tl dr  Use either of the Map implementations bundled with Java 6 and later that implement NavigableMap  the successor to SortedMap     Use TreeMap if running single-threaded  or if the map is to be read-only across threads after first being populated   Use ConcurrentSkipListMap if manipulating the map across threads    NavigableMap  FYI  the SortedMap interface was succeeded by the NavigableMap interface   You would only need to use SortedMap if using 3rd-party implementations that have not yet declared their support of NavigableMap  Of the maps bundled with Java  both of the implementations that implement SortedMap also implement NavigableMap    Interface versus concrete class     s SortedMap the best answer  TreeMap     As others mentioned  SortedMap is an interface while TreeMap is one of multiple implementations of that interface  and of the more recent NavigableMap    Having an interface allows you to write code that uses the map without breaking if you later decide to switch between implementations   NavigableMap lt  Employee   Project  gt  currentAssignments   new TreeSet lt  gt      currentAssignments put  alice   writeAdCopyProject      currentAssignments put  bob   setUpNewVendorsProject        This code still works if later change implementations  Perhaps you later need a map that supports concurrency for use across threads  Change that declaration to   NavigableMap lt  Employee   Project  gt  currentAssignments   new ConcurrentSkipListMap lt  gt           and the rest of your code using that map continues to work   Choosing implementation  There are ten implementations of Map bundled with Java 11  And more implementations provided by 3rd parties such as Google Guava    Here is a graphic table I made highlighting the various features of each  Notice that two of the bundled implementations keep the keys in sorted order by examining the key   s content  Also  EnumMap keeps its keys in the order of the objects defined on that enum  Lastly  the LinkedHashMap remembers original insertion order

User · Answer

TreeMap sorts by the key natural ordering  The keys should implement Comparable or be compatible with a Comparator  if you passed one instance to constructor   In you case  Float already implements Comparable so you don t have to do anything special   You can call keySet to retrieve all the keys in ascending order

User · Answer

You can use TreeMap which internally implements the SortedMap below is the example   Sorting by ascending ordering      Map lt Float  String gt  ascsortedMAP   new TreeMap lt Float  String gt        ascsortedMAP put 8f   name8      ascsortedMAP put 5f   name5      ascsortedMAP put 15f   name15      ascsortedMAP put 35f   name35      ascsortedMAP put 44f   name44      ascsortedMAP put 7f   name7      ascsortedMAP put 6f   name6       for  Entry lt Float  String gt  mapData   ascsortedMAP entrySet          System out println  Key       mapData getKey      Value       mapData getValue           Sorting by descending ordering    If you always want this create the map to use descending order in general  if you only need it once create a TreeMap with descending order and put all the data from the original map in        Create the map and provide the comparator as a argument   Map lt Float  String gt  dscsortedMAP   new TreeMap lt Float  String gt  new Comparator lt Float gt           Override     public int compare Float o1  Float o2          return o2 compareTo o1                 dscsortedMAP putAll ascsortedMAP     for further information about SortedMAP read http   examples javacodegeeks com core-java util treemap java-sorted-map-example

[java] How to use SortedMap interface in Java?

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