TreeMap headMap() Method in Java Last Updated : 09 Jul, 2018 Comments Improve Suggest changes Like Article Like Report The java.util.TreeMap.headMap(key_point) method of TreeMap class is used to get all the pairs or portion of the map strictly less than the parameter key_value. The mentioned parameter is excluded from the newly prepared treemap. Since the set is backed by the map, so any changes to the map are reflected in the other map, and vice-versa. Syntax: sorted_map = old_treemap.headMap(key_point) Parameters: The method takes one parameter key_point of the type of key taken in the TreeMap and refers to the point, till which the key-value pair is to be returned. Return Value: The method returns the portion of the treemap whose keys are strictly less than that of the key_point. Exceptions: The method throws three type of exceptions: ClassCastException: This exception is thrown when the key_point is not compatible or comparable to the maps comparator. NullPointerException: This exception is thrown when key-point is Null. IllegalArgumentException: This exception is thrown when the key_point is out of bound or outside the limit of the map range. Below programs illustrate the use of java.util.TreeMap.headMap() method: Program 1: Java // Java code to illustrate the get() method import java.util.*; public class Tree_Map_Demo { public static void main(String[] args) { // Creating an empty TreeMap TreeMap<Integer, String> tree_map = new TreeMap<Integer, String>(); // Mapping string values to int keys tree_map.put(10, "Geeks"); tree_map.put(15, "4"); tree_map.put(20, "Geeks"); tree_map.put(25, "Welcomes"); tree_map.put(30, "You"); // Displaying the TreeMap System.out.println("Initial Tree is: " + tree_map); // Creating the sorted map for map head SortedMap<Integer, String> map_head = new TreeMap<Integer, String>(); map_head = tree_map.headMap(20); // Getting the map head System.out.println("The headmap is: " + map_head); } } Output: Initial Tree is: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You} The headmap is: {10=Geeks, 15=4} Program 2: Java // Java code to illustrate the get() method import java.util.*; public class Tree_Map_Demo { public static void main(String[] args) { // Creating an empty TreeMap TreeMap<String, Integer> tree_map = new TreeMap<String, Integer>(); // Mapping int values to string keys tree_map.put("Geeks", 10); tree_map.put("4", 15); tree_map.put("Geeks", 20); tree_map.put("Welcomes", 25); tree_map.put("You", 30); // Displaying the TreeMap System.out.println("Initial Tree is: " + tree_map); // Creating the sorted map for map head SortedMap<String, Integer> map_head = new TreeMap<String, Integer>(); map_head = tree_map.headMap("You"); // Getting the map head System.out.println("The headmap is: " + map_head); } } Output: Initial Tree is: {4=15, Geeks=20, Welcomes=25, You=30} The headmap is: {4=15, Geeks=20, Welcomes=25} Note: The same operation can be performed with any type of Mappings with variation and combination of different data types. Comment More infoAdvertise with us Next Article TreeMap keySet() Method in Java with Examples chinmoy lenka Follow Improve Article Tags : Misc Java Java-Collections java-TreeMap Practice Tags : JavaJava-CollectionsMisc Similar Reads TreeMap in Java TreeMap is a part of the Java Collection Framework. It implements the Map and NavigableMap interface and extends the AbstractMap class. It stores key-value pairs in a sorted order based on the natural ordering of keys or a custom Comparator. It uses a Red-Black Tree for efficient operations (add, re 11 min read Java TreeMap clear() Method The clear() method is a built-in method of the TreeMap class in Java of the java.util package. This method is used to remove all key-value mappings from the TreeMap. And after invoking this method, the map becomes completely empty.This method is very useful when we want to reset the map or discard a 2 min read TreeMap clone() Method in Java with Examples In Java, clone() method of the TreeMap class is used to return a shallow copy of the mentioned treemap. It just creates a copy of the map. --> java.util Package --> TreeMap Class --> clone() Method Syntax: Tree_Map.clone() Parameters: The method does not take any parameters. Return Type: A 2 min read Java TreeMap containsKey() Method The containsKey() method in Java is used to check if a given key exists in a TreeMap. If the key is present in the map, it returns true, otherwise, it returns false. This method is very helpful when we need to verify whether a mapping exists before performing any operation on it.Syntax of TreeMap co 3 min read TreeMap containsValue() Method in Java With Examples In Java, containsValue() method of the TreeMap class is used to check whether a particular value is being mapped by any key in the TreeMap. It takes the value as a parameter and returns True if that value is mapped by any of the keys in the map. --> java.util Package --> TreeMap class --> c 3 min read TreeMap entrySet() Method in Java The java.util.TreeMap.entrySet() method in Java is used to create a set out of the same elements contained in the treemap. It basically returns a set view of the treemap or we can create a new set and store the map elements into them. Syntax: tree_map.entrySet() Parameters: The method does not take 2 min read TreeMap firstEntry() and firstKey() Method in Java with Examples There are two variants of first() in Java.util.TreeMap, both are discussed in this article. Method 1: firstEntry() It returns a key-value mapping associated with the least key in this map, or null if the map is empty. Syntax: public Map.Entry firstEntry() Return Type: An entry with the least key and 3 min read Java TreeMap get() Method The get() method of the TreeMap class in Java is used to retrieve or fetch the value mapped by a particular key mentioned in the parameter. If the key does not exist in the map, the method returns null.Syntax of TreeMap get() MethodtreeMap.get(Object key)Parameter: key: The method takes one paramete 2 min read TreeMap headMap() Method in Java The java.util.TreeMap.headMap(key_point) method of TreeMap class is used to get all the pairs or portion of the map strictly less than the parameter key_value. The mentioned parameter is excluded from the newly prepared treemap. Since the set is backed by the map, so any changes to the map are refle 3 min read TreeMap keySet() Method in Java with Examples In Java, keySet() method of TreeMap class is present inside java.util package in Java is used to create a set out of the key elements contained in the treemap. It basically returns a set view of the keys or we can create a new set and store the key elements in them in ascending order. Since the set 3 min read Like