Comparator Vs Comparable

• Java provide two interfaces to sort objects using data members

Comparable

• here we need to implements Comparable to our class
• override the method compareTo

  public int compareTo(Movie m)
    {
        return this.year - m.year;
    }
  

• calling Collections.sort will sort the Movie Object based on year

class Movie implements Comparable<Movie>
{
    private double rating;
    private String name;
    private int year;

    // Used to sort movies by year
    public int compareTo(Movie m)
    {
        return this.year - m.year;
    }

    // Constructor
    public Movie(String nm, double rt, int yr)
    {
        this.name = nm;
        this.rating = rt;
        this.year = yr;
    }

    // Getter methods for accessing private data
    public double getRating() { return rating; }
    public String getName() { return name; }
    public int getYear()     { return year; }
}

// Driver class
class Main
{
    public static void main(String[] args)
    {
        ArrayList<Movie> list = new ArrayList<Movie>();
        list.add(new Movie("Force Awakens", 8.3, 2015));
        list.add(new Movie("Star Wars", 8.7, 1977));
        list.add(new Movie("Empire Strikes Back", 8.8, 1980));
        list.add(new Movie("Return of the Jedi", 8.4, 1983));

        Collections.sort(list);

        System.out.println("Movies after sorting : ");
        for (Movie movie: list)
        {
            System.out.println(movie.getName() + " " +
                            movie.getRating() + " " +
                            movie.getYear());
        }
    }
}

Comparator

• here separate class is needed to implement Comparator
• method name is compare
• here we compare two objects and return , -1 , 1 , 0
• how to call
• ` RatingCompare ratingCompare = new RatingCompare();

    `Collections.sort(list, ratingCompare);`
  

Example

```java


// Class to compare Movies by ratings
class RatingCompare implements Comparator<Movie>
{
    public int compare(Movie m1, Movie m2)
    {
        if (m1.getRating() < m2.getRating()) return -1;
        if (m1.getRating() > m2.getRating()) return 1;
        else return 0;
    }
}

// Class to compare Movies by name
class NameCompare implements Comparator<Movie>
{
    public int compare(Movie m1, Movie m2)
    {
        return m1.getName().compareTo(m2.getName());
    }
}


        RatingCompare ratingCompare = new RatingCompare();
        Collections.sort(list, ratingCompare);

        // Call overloaded sort method with RatingCompare
        // (Same three steps as above)
        System.out.println("\nSorted by name");
        NameCompare nameCompare = new NameCompare();
        Collections.sort(list, nameCompare);


        // Uses Comparable to sort by year
        System.out.println("\nSorted by year");
        Collections.sort(list);

    }
}