Why does Collections.unmodifiableList() still change sometimes?

It creates a read-only view, not a copy. If the original list changes, the unmodifiable view reflects those changes.

String str1=new String("prakash");
String str2=new String("prakash");
System.out.println(str1==str2);

String str1=new String("prakash");
String str2=new String("prakash");
System.out.println(str1==str2);