How does a comparable and comparator work internally?

Asked By: Onisor Nebra | Last Updated: 24th April, 2020
Category: technology and computing programming languages
4.1/5 (543 Views . 24 Votes)
With Comparable, your class needs to implement the comparable interface and you need to override its compareTo method. So when you call the Collections. sort method on an object of your class, your implementation of the compareTo method is called INTERNALLY, and the objects are sorted accordingly.

Click to see full answer


Beside this, what is the difference between comparable and comparator?

Comparable v/s Comparator in Java Comparable interface is used to sort the objects with natural ordering. Comparator in Java is used to sort attributes of different objects. Comparable interface compares “this” reference with the object specified. Comparator provides compare() method, equals() method to sort elements.

Additionally, how do you sort an employee object using comparator and comparable? Difference Between Comparable and Comparator

  1. Java.
  2. To implements comparable interface, class must implement a single method compareTo()
  3. int a.
  4. A comparable object is comparing itself with another object.
  5. You must modify the class whose instance you want to sort.
  6. So that only one sort sequence can be created per class.

Similarly, you may ask, how do you use comparator and comparable?

Comparable vs Comparator

  1. Comparable interface can be used to provide single way of sorting whereas Comparator interface is used to provide different ways of sorting.
  2. For using Comparable, Class needs to implement it whereas for using Comparator we don't need to make any change in the class.

How do you compare two different objects?

If the two objects have the same values, equals() will return true . In the second comparison, equals() checks to see whether the passed object is null, or if it's typed as a different class. If it's a different class then the objects are not equal. Finally, equals() compares the objects' fields.

38 Related Question Answers Found

What is the main purpose of comparator interface?

Methods of Java Comparator Interface
It compares the first object with the second object. It is used to compare the current object with the specified object. It is used to compare the current object with the specified object.

Can we override compareTo method?

Override compareTo Method
It should return a negative integer(usually -1), if the current triggering object is less than the passed one, and positive integer (usually +1) if greater than, and 0 if equal. compareTo method should throws an exception if the passed object has incompatible type or null.

Which one is better comparable or comparator?

Comparable should be used when you compare instances of same class. Comparator can be used to compare instances of different classes. Comparable is implemented by class which need to define a natural ordering for its objects.

How do you use compareTo?

The Java String compareTo() method is used for comparing two strings lexicographically. Each character of both the strings is converted into a Unicode value for comparison. If both the strings are equal then this method returns 0 else it returns positive or negative value.

How do I sort using comparator?


Pass Comparator as argument to sort() method
sort (and Arrays. sort ), allow precise control over the sort order. In the following example, we obtain a Comparator that compares Person objects by their age. Comparator<Person> byAge = Comparator.

How does a TreeMap work?

TreeMap in Java. The TreeMap is used to implement Map interface and NavigableMap along with the Abstract Class. Also, all its elements store in the TreeMap are sorted by key. TreeMap performs sorting in natural order on its key, it also allows you to use Comparator for custom sorting implementation.

Is comparator an interface?

Method 2: Using comparator interface- Comparator interface is used to order the objects of user-defined class. This interface is present in java. util package and contains 2 methods compare(Object obj1, Object obj2) and equals(Object element). Using comparator, we can sort the elements based on data members.

How do you use collection sort?

By default, Collection. sort performs the sorting in ascending order. If we want to sort the elements in reverse order we could use following methods: reverseOrder() : Returns a Comparator that imposes the reverse of natural ordering of elements of the collection.

How can we sort the elements of an object?

To sort an Object by its property, you have to make the Object implement the Comparable interface and override the compareTo() method. Lets see the new Fruit class again. The new Fruit class implemented the Comparable interface, and overrided the compareTo() method to compare its quantity property in ascending order.

What is comparable interface?


Java Comparable interface is used to order the objects of the user-defined class. This interface is found in java. lang package and contains only one method named compareTo(Object). It provides a single sorting sequence only, i.e., you can sort the elements on the basis of single data member only.

What is the difference between Array and ArrayList?

1- First and Major difference between Array and ArrayList in Java is that Array is a fixed length data structure while ArrayList is a variable length Collection class. You can not change length of Array once created in Java but ArrayList re-size itself when gets full depending upon capacity and load factor.

Can we sort HashMap in Java?

HashMap is not meant to keep entries in sorted order, but if you have to sort HashMap based upon keys or values, you can do that in Java. Sorting HashMap on keys is quite easy, all you need to do is to create a TreeMap by copying entries from HashMap. This is similar of how you sort an ArrayList in Java.

How do you sort an ArrayList?

To sort the ArrayList, you need to simply call the Collections. sort() method passing the ArrayList object populated with country names. This method will sort the elements (country names) of the ArrayList using natural ordering (alphabetically in ascending order).

What does the hashCode () method?

Java hashCode()
Java Object hashCode() is a native method and returns the integer hash code value of the object. If two objects are equal according to equals() method, then their hash code must be same. If two objects are unequal according to equals() method, their hash code are not required to be different.

Why is comparable not a functional interface?


1 Answer. Comparable is technically a functional interface, but it makes no sense to actually implement it with a lambda. Comparable objects really have to have other state that you're trying to compare, and you're supposed to compare two objects of the same type. Neither of those make sense for a lambda.

What is Java priority queue?

A priority queue in Java is a special type of queue wherein all the elements are ordered as per their natural ordering or based on a custom Comparator supplied at the time of creation. The Priority Queue class is part of Java's collections framework and implements the Queue interface.

Why is string immutable in Java?

The string is Immutable in Java because String objects are cached in String pool. Another reason of why String class is immutable could die due to HashMap. Since Strings are very popular as HashMap key, it's important for them to be immutable so that they can retrieve the value object which was stored in HashMap.