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What is the difference between headMap(), tailMap() and subMap() methods of NavigableMap?

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Pragya Keshap answered on February 4, 2023 Popularity 1/10 Helpfulness 1/10

answer What is the difference between headMap(), tailMap() and subMap() methods of NavigableMap?

What is the difference between headMap(), tailMap() and subMap() methods of NavigableMap?

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The headMap() method returns a view of the original

NavigableMap that contains the elements that are less than a given

element.

NavigableMap original = new TreeMap();

original.put("1", "1");

original.put("2", "2");

original.put("3", "3");

//this headmap1 will contain elements "1" and "2"

SortedMap headmap1 = original.headMap("3");

//this headmap2 will contain elements "1", "2", and "3" because

"inclusive"=true

NavigableMap headmap2 = original.headMap("3", true);

The tailMap() method works similar to headMap() method, but it

returns all elements that are higher than the given input element.

The subMap() method accepts two parameters demarcating the

boundaries of the view map to return.

All the three methods return a subset of the original map in a view

form.

public class NavigableMapExample {

    public static void main(String args[]) {
     
        //NavigableMap extends SortedMap to provide useful navigation methods
        NavigableMap<String, String> navigableMap = new TreeMap<String, String>();
     
        navigableMap.put("C++", "Good programming language");
        navigableMap.put("Java", "Another good programming language");
        navigableMap.put("Scala", "Another JVM language");
        navigableMap.put("Python", "Language which Google use");
     
        System.out.println("SorteMap : " + navigableMap);
     
        //lowerKey returns key which is less than specified key
        System.out.println("lowerKey from Java : "
                + navigableMap.lowerKey("Java"));
     
        // floorKey returns key which is less than
        // or equal to specified key
        System.out.println("floorKey from Java: "
          + navigableMap.floorKey("Java"));
     
        //ceilingKey returns key which is greater than
        // or equal to specified key
        System.out.println("ceilingKey from Java: "
           + navigableMap.ceilingKey("Java"));
     
        //higherKey returns key which is greater specified key
        System.out.println("higherKey from Java: "
           + navigableMap.higherKey("Java"));
     
     
        //Apart from navigation methods,
        // it also provides a useful method
        //to create subMap from existing Map 
        //  tailMap, headMap and subMap
     
        //an example of headMap - returns NavigableMap whose key is less than specified
        NavigableMap<String, String> headMap = navigableMap.headMap("Python", false);
        System.out.println("headMap created form navigableMap : " + headMap);
             
        //an example of tailMap - returns NavigableMap whose key is greater than specified
        NavigableMap<String, String> tailMap = navigableMap.tailMap("Scala", false);
        System.out.println("tailMap created form navigableMap : " + tailMap);
     
        //an example of subMap - return NavigableMap from toKey to fromKey
        NavigableMap<String, String> subMap
                  = navigableMap.subMap("C++", false 
                                         ,"Python", false);
        System.out.println("subMap created form navigableMap : "
                                      + subMap);
    }
}


Read more: https://javarevisited.blogspot.com/2013/01/what-is-navigablemap-in-java-6-example-submap-head-tail.html#ixzz7sNurbjTu

https://javarevisited.blogspot.com/2013/01/what-is-navigablemap-in-java-6-example-submap-head-tail.html#axzz7sNmYn2qu

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Contributed on Feb 04 2023

Pragya Keshap

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What is the difference between headMap(), tailMap() and subMap() methods of NavigableMap?

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