How to remove duplicate objects in a List without equals/hashcode?

Question

I have to remove duplicated objects in a List. It is a List from the object Blog that looks like this:

public class Blog {
    private String title;
    priv         


        

Answer 1

And i can't alter the object. I can't put new methods on it.

How do i do this?

In case you also mean how do I make the object immutable and prevent subclassing: use the final keyword

public final class Blog { //final classes can't be extended/subclassed
   private final String title; //final members have to be set in the constructor and can't be changed
   private final String author;
   private final String url;
   private final String description;
    ...
}

Edit: I just saw some of your comments and it seems you want to change the class but can't (third party I assume).

To prevent duplicates you might use a wrapper that implements appropriate equals() and hashCode(), then use the Set aproach mentioned by the others:

 class BlogWrapper {
   private Blog blog; //set via constructor etc.

   public int hashCode() {
     int hashCode = blog.getTitle().hashCode(); //check for null etc.
     //add the other hash codes as well
     return hashCode;
   }

   public boolean equals(Object other) {
     //check if both are BlogWrappers
     //remember to check for null too!
     Blog otherBlog = ((BlogWrapper)other).getBlog(); 
     if( !blog.getTitle().equals(otherBlog.getTitle()) {
       return false;
     }
     ... //check other fields as well
     return true
   }
 }

Note that this is just a rough and simple version and doesn't contain the obligatory null checks.

Finally use a Set, loop through all the blogs and try to add new BlogWrapper(blog) to the set. In the end, you should only have unique (wrapped) blogs in the set.