To check if a key exists in TreeMap in Java, you need to call the method containsKey() of the TreeMap.

public boolean containsKey(): This method returns a true Boolean if the key you are looking for is in the TreeMap.

listTo get the value of the key you are looking for in TreeMap in Java, you need to call the get(key).

public Object get(Object key): this method returns the value of the key you are looking for if it exists.

import java.util.*; 

public class recherche_treemap {
 public static void main(String[] args) {
 // creating TreeMap
 TreeMap< String, String> treemap_langue = new TreeMap< String, String> (); 
 
 // insertion in treemap
 treemap_langue.put("fr", "français"); 
 treemap_langue.put("en", "English"); 
 treemap_langue.put("es", "Spanish"); 
 treemap_langue.put("it", "Italian"); 
 treemap_langue.put("ge", "German"); 
 
 //browse keys with Iterator
 System.out.println("Code List"); 
 Set set=treemap_langue.keySet(); 
 Iterator iterator = set.iterator(); 
 while(iterator.hasNext()){
 String key = ((String) iterator.next()); 
 System.out.println(key); 
 }
 
 boolean exists = treemap_langue.containsKey("es"); 
 System.out.println("the es key exists in the list: "+exists); 
 
 String value = treemap_langue.get("en"); 
 System.out.println("en is the code for: "+value); 
 } 
}

The execution of this code gives:

Code List
en
es
fr
ge
it
the es key exists in the list:  true
en is the code for: english

References:
JavaDoc: containsKey() method