Java Program to convert a Map to a read only map

Let’s say the following is our Map −

Map<String, String>map = new HashMap<String,String>();
map.put("1","A");
map.put("2","B");
map.put("3","C");

Make it read-only using the unmodifiableMap() method −

map = Collections.unmodifiableMap(map);

Example

 Live Demo

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
public class Demo {
   public static void main(String[] argv) throws Exception {
      Map<String, String>map = new HashMap<String,String>();
      map.put("1","A");
      map.put("2","B");
      map.put("3","C");
      // making it read-only
      map = Collections.unmodifiableMap(map);
      try {
         map.put("4","D");
         map.put("5","E");
         map.put("6","F");
      } catch (UnsupportedOperationException e) {
         System.out.println(e.getMessage());
      }
   }
}

Output

null