java - How to remove duplicate objects in a List<MyObject> 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;
    private String author;
    private String url;
    private String description;
    ...
}

A duplicated object is an object that have title, author, url and description equal to other object.

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

How do I do this?

Answer 1

Here is the complete code which works for this scenario:

class Blog {
    private String title;
    private String author;
    private String url;
    private String description; 

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    Blog(String title, String author, String url, String description)
    {
        this.title = title;
        this.author = author;
        this.url = url;
        this.description = description; 
    }

    @Override
    public boolean equals(Object obj) {
        // TODO Auto-generated method stub
        if(obj instanceof Blog)
        {
            Blog temp = (Blog) obj;
            if(this.title.equals(temp.title) && this.author.equals(temp.author) && this.url.equals(temp.url) && this.description.equals(temp.description))
                return true;
        }
        return false;
    }

    @Override
    public int hashCode() {
        // TODO Auto-generated method stub
        
        return (this.title.hashCode() + this.author.hashCode() + this.url.hashCode() + this.description.hashCode());        
    }
}

Here is the main function which will eliminate the duplicates:

public static void main(String[] args) {
    Blog b1 = new Blog("A", "sam", "a", "desc");
    Blog b2 = new Blog("B", "ram", "b", "desc");
    Blog b3 = new Blog("C", "cam", "c", "desc");
    Blog b4 = new Blog("A", "sam", "a", "desc");
    Blog b5 = new Blog("D", "dam", "d", "desc");
    List<Blog> list = new ArrayList();
    list.add(b1);
    list.add(b2);
    list.add(b3);
    list.add(b4);       
    list.add(b5);
    
    //Removing Duplicates;
    Set<Blog> s= new HashSet<Blog>();
    s.addAll(list);         
    list = new ArrayList<Blog>();
    list.addAll(s);        
    //Now the List has only the identical Elements
}