Java / immutable objects - example: String object

What are immutable objects?
Immutable object are objects whose state cannot be changed.

Example of immutable object (String):

public class MyImmutable 
{
 public static void main(String[] args) 
 {
  String myString = new String( "my string" );
  
  myString.replace("my", "my new");
  System.out.println("Original String (immutable): " + myString);
  
  String newMyString = myString.replace("my", "my new");
  System.out.println("New String: " + newMyString);  
 }
}

Java official immutable tutorial