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

You can use TreeMap which internally implements the SortedMap below is the example

Sorting by ascending ordering :

  Map<Float, String> ascsortedMAP = new TreeMap<Float, String>();

  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<Float, String> 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<Float, String> dscsortedMAP = new TreeMap<Float, String>(new Comparator<Float>() {
    @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/

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

A TreeMap is probably the most straightforward way of doing this   You use it exactly like a normal Map  i e   Map lt Float String gt  mySortedMap   new TreeMap lt Float MyObject gt        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 lt Float String gt  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

[java] How to use SortedMap interface in Java?

Examples related to java

Examples related to sortedmap