What is TreeMap in Java?

Methods of TreeMap

TreeMap offers a wide collection of methods that helps in performing different functions. They are:

• clear(): All the mapping in the map will be removed.
• clone(): A shallow copy will be returned for the TreeMap instance.
• containsKey(Objectk): If there is mapping available for the specified key, true will be returned.
• containsValue(Objectv): If there is mapping available for one or more keys for the value v, true will be returned.
• ceilingKey(Kkey): Least key which is larger than or equal to the specified key will be returned. If there is no key, then null will be returned.
• ceilingEntry(Kkey): Key-value pair for the least key, which is larger than or equal to the specified key will be returned. If there is no key, then null will be returned.
• firstKey(): First or last key in the map will be returned.
• firstEntry(): Key-value pair for the least or first key in the map will be returned. If there is no key, then null will be returned.
• floorKey(Kkey): The Largest key, which is less than or equal to the specified key, will be returned. If there is no key, then null will be returned.
• floorEntry(Kkey): Key-value pair for the largest key, which is less than or equal to the specified key, will be returned. If there is no key, then null will be returned.
• lastKey(): Highest or last key in the map will be returned.
• lastEntry(): Key-value pair for the largest key in the map will be returned. If there is no key, then null will be returned.
• lowerKey(Kkey): The Largest key, which is strictly smaller than the specified key, will be returned. If there is no key, then null will be returned.
• lowerEntry(Kkey): Key-value pair for the largest key, which is strictly smaller than the specified key, will be returned. If there is no key, then null will be returned.
• remove(Objectk): Mapping for the specified key in the map will be removed.
• size(): Count of key-value pairs in the map will be returned.
• higherEntry(Kkey): Key-value pair for the smallest key, which is strictly larger than the specified key, will be returned. If there is no key, then null will be returned.
• higherKey(Kkey): The Smallest key, which is strictly higher than the specified key, will be returned. If there is no key, then null will be returned.
• descendingMap(): Reverse order will be returned for the mappings.
• entrySet(): Set view will be returned for the mappings.
• get(Objectk): The value of the specified key will be returned. If the key does not contain any mapping, then null will be returned.
• keySet(): Set view will be returned for the keys.
• navigableKeySet(): NavigableSet view will be returned for the keys.
• pollFirstEntry(): Key-value pair for the least or first key in the map will be removed and returned. If the map is empty, then null will be returned.
• pollLastEntry(): Key-value pairs for the greatest key in the map will be removed and returned. If the map is empty, then null will be returned.
• values(): Collection view will be returned for the values in the map.

Example to Implement TreeMap in Java

Now, let us see a sample program to create a treemap and add elements to it.

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
public class TreeMapExample {
public static void main(String args[]) {
// Tree Map creation
TreeMap tmap = new TreeMap();
// Add elements to the treemap tmap
tmap.put("Anna Jeshua", new Double(3459.70));
tmap.put("Annamu Jeshua", new Double(321.56));
tmap.put("Izanorah Denan", new Double(1234.87));
tmap.put("Adam Jeshua", new Double(89.35));
tmap.put("Anabeth Jeshua", new Double(-20.98));
// Retrieve the entry set of treemap
Set set = tmap.entrySet();
// Create an iterator itr
Iterator itr = set.iterator();
// Display the elements in treemap using while loop
while(itr.hasNext()) {
Map.Entry mp = (Map.Entry)itr.next();
System.out.print(" Key : " + mp.getKey() + ";");
System.out.println(" Value : "+ mp.getValue());
}
System.out.println();
// Add 2500 to Anabeth's value
double val = ((Double)tmap.get("Anabeth Jeshua")).doubleValue();
tmap.put("Anabeth Jeshua", new Double(val + 2500));
System.out.println("Anabeth's new value: " + tmap.get("Anabeth Jeshua"));
} }

Output:

Keys and corresponding values of the TreeMap will be displayed on executing the code.

Explanation:

• Firstly, create a TreeMap and add elements to it.
• In order to display the elements, an iterator has to be created.
• Using the iterator, all the keys and their corresponding values are displayed.
• To add 2500 to a key’s value, the put() method is also used.

Conclusion

Java TreeMap is an implementation of the Red-Black tree that helps in storing key-value pairs in sorted order. In this document, several details such as declaration, constructors, methods, and sample program of Java TreeMap is discussed in detail.

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