TreeMap SortedMap headMap(K toKey) Method Example Program


Returns a view of the portion of this map whose keys are strictly less than toKey. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports.

Program

package com.candidjava;

import java.util.TreeMap;
import java.util.SortedMap;

/**
 * @author: Hari Haran
 * @discription:TheheadMap(K toKey) method is used to return a view of the
 *                           portion of this map whose keys are strictly less
 *                           than toKey.
 */

public class TreeMapHeadMap {
	public static void main(String[] args) {

		TreeMap<Integer, String> tm = new TreeMap<Integer, String>();
		SortedMap<Integer, String> tmhead = new TreeMap<Integer, String>();

		tm.put(1, "Anand");
		tm.put(2, "Hari Haran");
		tm.put(8, "Kamal");
		tm.put(4, "Karthikeyan");
		tm.put(5, "Mohan");
		tm.put(6, "Vinoth");
		tm.put(7, "Hari Haran");

		tmhead = tm.headMap(3);

		System.out.println("Checking values of the sorted map");
		System.out.println("Value is: " + tmhead);
	}
}

Output

Checking values of the sorted map
Value is: {1=Anand, 2=Hari Haran}

Explanation

public SortedMap<K,V> headMap(K toKey)
Returns a view of the portion of this map whose keys are strictly less than toKey. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports.
The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Equivalent to headMap(toKey, false).

Specified by:
headMap in interface NavigableMap<K,V>
Specified by:
headMap in interface SortedMap<K,V>
Parameters:
toKey - high endpoint (exclusive) of the keys in the returned map
Returns:
a view of the portion of this map whose keys are strictly less than toKey
Throws:
ClassCastException - if toKey is not compatible with this map's comparator (or, if the map has no comparator, if toKey does not implement Comparable). Implementations may, but are not required to, throw this exception if toKey cannot be compared to keys currently in the map.
NullPointerException - if toKey is null and this map uses natural ordering, or its comparator does not permit null keys
IllegalArgumentException - if this map itself has a restricted range, and toKey lies outside the bounds of the range


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