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

Here is the complete code which works for this scenario:

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

    private String 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 == temp.title && this.author== temp.author && this.url == temp.url && this.description == 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
}

If you can't edit the source of the class (why not?), then you need to iterate over the list and compare each item based on the four criteria mentioned ("title, author, url and description").

To do this in a performant way, I would create a new class, something like BlogKey which contains those four elements and which properly implements equals() and hashCode(). You can then iterate over the original list, constructing a BlogKey for each and adding to a HashMap:

Map<BlogKey, Blog> map = new HashMap<BlogKey, Blog>();
for (Blog blog : blogs) {
     BlogKey key = createKey(blog);
     if (!map.containsKey(key)) {
          map.put(key, blog);
     }
}
Collection<Blog> uniqueBlogs = map.values();

However the far simplest thing is to just edit the original source code of Blog so that it correctly implements equals() and hashCode().

Make sure Blog has methods equals(Object) and hashCode() defined, and addAll(list) then to a new HashSet(), or new LinkedHashSet() if the order is important.

Better yet, use a Set instead of a List from the start, since you obviously don't want duplicates, it's better that your data model reflects that rather than having to remove them after the fact.