java.util.TreeMap.headMap() Method
Description
TheheadMap(K toKey,boolean inclusive) method is used to return a view of the portion of this map whose keys are less than (or equal to, if inclusive is true)toKey.
Declaration
Following is the declaration for java.util.TreeMap.headMap() method.
public NavigableMap<K,V> headMap(K toKey,boolean inclusive)
Parameters
toKey − This is the high endpoint of the keys in the returned map.
inclusive − This is true if the high endpoint is to be included in the returned view.
Return Value
The method call returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey.
Exception
ClassCastException − This exception is thrown if toKey is not compatible with this map's comparator.
NullPointerException − This exception is thrown if toKey is null and this map uses natural ordering, or its comparator does not permit null keys.
IllegalArgumentException − This exception is thrown if this map itself has a restricted range, and toKey lies outside the bounds of the range.
Example
The following example shows the usage of java.util.TreeMap.headMap() method.
package com.tutorialspoint;
import java.util.*;
public class TreeMapDemo {
public static void main(String[] args) {
// creating maps
TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();
NavigableMap<Integer, String> treemapheadincl = new TreeMap<Integer, String>();
// populating tree map
treemap.put(2, "two");
treemap.put(1, "one");
treemap.put(3, "three");
treemap.put(6, "six");
treemap.put(5, "five");
// getting head map inclusive 3
treemapheadincl = treemap.headMap(3,true);
System.out.println("Checking values of the map");
System.out.println("Value is: "+ treemapheadincl);
}
}
Let us compile and run the above program, this will produce the following result.
Checking values of the map
Value is: {1=one, 2=two, 3=three}