Check If a Particular Value Exists in TreeMap in Java

In this article, we will learn to check if a particular value exists in TreeMap in Java. A Java TreeMap is an ordered map that keeps key-value pairs in ascending order of keys. Although it is efficient to look up a key, checking for a value is inefficient since one has to iterate over the values.

What is TreeMap?

A TreeMap is a Red-Black tree-based implementation it is a part of java.util package and implements the NavigableMap interface. It maintains the natural ordering of keys or a custom order defined by a Comparator. Since it is sorted by keys, searching for values is not as efficient as searching for keys.

Checking if a Value Exists in TreeMap

To check if a particular value exists in TreeMap, use the containsValue() method. This method returns true if the specified value is found; otherwise, it returns false.

boolean containsValue(Object value)

• Parameters: The value to be checked for existence.
  
• Returns: true if the value exists, false otherwise.

Create a TreeMap first and add some elements using the put() method ?

TreeMap<Integer,String> m = new TreeMap<Integer,String>();
m.put(1,"PHP");
m.put(2,"jQuery");
m.put(3,"JavaScript");
m.put(4,"Ruby");
m.put(5,"Java");
m.put(6,"AngularJS");
m.put(7,"ExpressJS");

Now, let's say we need to check whether the value "Java" exists or not. For that, use the containsValue() method like this ?

m.containsValue("Java")

Example

The following is an example to check if a particular value exists in TreeMap ?

import java.util.*;
public class Demo {
   public static void main(String args[]) {
      TreeMap<Integer,String> m = new TreeMap<Integer,String>();
      m.put(1,"PHP");
      m.put(2,"jQuery");
      m.put(3,"JavaScript");
      m.put(4,"Ruby");
      m.put(5,"Java");
      m.put(6,"AngularJS");
      m.put(7,"ExpressJS");
      System.out.println("TreeMap Elements...\n"+m);
      System.out.println("Does value PHP exist in the TreeMap = "+m.containsValue("Java"));
   }
}

Output

TreeMap Elements...
{1=PHP, 2=jQuery, 3=JavaScript, 4=Ruby, 5=Java, 6=AngularJS, 7=ExpressJS}
Does value PHP exist in the TreeMap = true

Time complexity: O(n), as it iterates through all values.
Space complexity: O(1), since it does not use extra space.

Conclusion

The containsValue() method is a simple and effective way to check if a specific value exists in a TreeMap. However, since it requires scanning all values, its time complexity is O(n), making it less efficient than key lookups. If frequent value searches are needed, consider using a bi-directional map or maintaining an additional HashSet of values for faster lookups.