ANGADJAVA Java Interview Question Java 8 Interview Questions: Comparable and Comparator Interfaces

Java 8 Interview Questions: Comparable and Comparator Interfaces

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Java 8 introduced several enhancements, and among them are improvements to the Comparable and Comparator interfaces. Let’s explore some common interview questions related to these interfaces.

1. What is the purpose of the Comparable interface in Java 8?

The Comparable interface in Java 8 is used for providing a natural ordering of objects. It defines a method compareTo() that establishes the default sorting order for objects of a class.

2. Could you demonstrate the implementation of Comparable in a class?

Certainly! Here’s an example using a Person class:

public class Person implements Comparable<Person> {
    private String name;
    private int age;

    // Constructors, getters, setters

    public int compareTo(Person otherPerson) {
        return, otherPerson.age);

3. What are the advantages and disadvantages of the Comparable interface?


  • Advantage: Provides a default ordering for objects without requiring external sorting logic.
  • Disadvantage: The natural ordering might not be suitable in all cases, and it cannot be changed easily.

Comparator Interface:

4. Explain the role of the Comparator interface in Java 8.

The Comparator interface allows the definition of multiple sorting criteria for objects. It provides flexibility in sorting and is particularly useful for classes that do not implement Comparable.

5. Can you provide an example of implementing a Comparator for sorting by names?

Certainly! Here’s an example using a PersonNameComparator:

public class PersonNameComparator implements Comparator<Person> {
    public int compare(Person person1, Person person2) {
        return person1.getName().compareTo(person2.getName());

6. How has Java 8 enhanced sorting with Comparator?

Java 8 introduced streamlined methods like comparing() for creating comparators with greater ease. Additionally, default methods such as reversed() enhance the functionality of comparators.

7. Can you demonstrate creating a comparator based on age using Java 8 features?

Certainly! Here’s an example using lambda expressions:

Comparator<Person> ageComparator = Comparator.comparingInt(Person::getAge);

Choosing Between Comparable and Comparator:

8. When would you use Comparable, and when would you prefer Comparator?


  • Use Comparable: When there is a clear and natural ordering for objects.
  • Use Comparator: When defining multiple sorting criteria or when dealing with classes that cannot be modified to implement Comparable.

9. How can you chain comparators to achieve multiple-level sorting?

Java 8 introduced the thenComparing method for chaining comparators. Here’s an example sorting by age and then by name:

Comparator<Person> combinedComparator = Comparator.comparingInt(Person::getAge).thenComparing(Person::getName);

10. How does Java 8 handle null values in comparators?

Java 8 provides methods like nullsFirst() and nullsLast() in the Comparator interface to effectively handle null values during comparison.

Comparator<Person> ageComparatorWithNullsFirst = Comparator.comparingInt(Person::getAge).nullsFirst();


Mastering the use of Comparable and Comparator interfaces is crucial for effective sorting in Java. These interview questions provide insights into a candidate’s understanding of these interfaces and their practical applications in Java 8.

Feel free to customize this template based on your specific needs or add more questions and scenarios as required.

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