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Java Program to demonstrate the use of TreeMap.

Java Code Example — Collection Programs

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Java Program to demonstrate the use of TreeMap.

Objective

Write a Java program to store and traverse Key-Value pairs using a TreeMap.

Algorithm / Approach

  1. Create a TreeMap.
  2. Use put(key, value) to insert Roll Numbers (Strings) as keys and Names as values.
  3. Retrieve a specific value using stud.get("1786").
  4. Extract all keys using stud.keySet() into a Set.
  5. Iterate through the keys using an Iterator, and use get(key) to print the corresponding values.
Test.java 
import java.util.*;
class Test {
 public static void main(String[] a) 
 {
  TreeMap stud = new TreeMap();
  stud.put("1001","Alok");
  stud.put("1005","Deepu");
  stud.put("1002","Anup");
  stud.put("1014","Ayan");
  stud.put("1049","Daneyal");
  stud.put("1786","Faiz");
  System.out.print("Student at 1786- ");
  System.out.println(stud.get("1786"));
  System.out.println("Traversing...");
  Set keys = stud.keySet();
  Iterator i = keys.iterator();
  while(i.hasNext()) {
   String x =(String) i.next();
   System.out.println(x+"- ");
   System.out.println(stud.get(x));
  }
 }
}

Expected Output

Student at 1786- Faiz
Traversing...
1001- Alok
1002- Anup
1005- Deepu
1014- Ayan
1049- Daneyal
1786- Faiz

Explanation of the Program

  • The Map interface is not a true Collection; it stores data in Key-Value pairs (like a dictionary in Python). Keys must be absolutely unique, but values can be duplicated.
  • A TreeMap specifically sorts the entries automatically based on the natural order of the KEYS.
  • Even though we inserted the Roll Numbers randomly (1001, 1005, 1002), when we iterate over the keySet(), they are retrieved in perfect numerical order.

Complexity

Time Complexity O(log n) - For put, get, and remove operations.
Space Complexity O(n)
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