How to use the SortedMap interface in Java?

Question

I have

Map<Float, MyObject> 

What is the best way to keep a map sorted by float?

Is SortedMap best answer? TreeMap ? How do i use this?

I create a map only once and often myMap.put() MyObject using myMap.put() and myMap.get() .

Answer 1

I would use TreeMap , which implements SortedMap . It is designed specifically for this.

Example:

 Map<Integer, String> map = new TreeMap<Integer, String>(); // Add Items to the TreeMap map.put(1, "One"); map.put(2, "Two"); map.put(3, "Three"); // Iterate over them for (Map.Entry<Integer, String> entry : map.entrySet()) { System.out.println(entry.getKey() + " => " + entry.getValue()); } 

See the Java tutorial page for SortedMap .
And here is a list of tutorials related to TreeMap.

Answer 2

TreeMap is probably the easiest way to do this. You use it just like a regular card.

t

  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 find out what else you can do with it.

Answer 3

You can use TreeMap, which internally implements SortedMap, below is an example

Sort Ascending:

  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()); } 

Sort Descending:

If you always want the top-down order to be used when creating the map, in general, if you need only once, create a TreeMap with the top-down order and put all the data from the original map.

  // 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 more information about SortedMAP read http://examples.javacodegeeks.com/core-java/util/treemap/java-sorted-map-example/

Answer 4

TreeMap, which is an implementation of the SortedMap interface, will work.

How to use it?

 Map<Float, MyObject> map = new TreeMap<Float, MyObject>(); 

Answer 5

TreeMap sorts by natural ordering. Keys must implement Comparable or be compatible with Comparator (if you passed one instance to the constructor). In this case, Float already implements Comparable , so you don’t have to do anything.

You can call keySet to get all the keys in ascending order.