Comparable defines a class's natural ordering by implementing compareTo in the class itself, while Comparator provides flexible, external custom sorting logic through compare; 1. Use Comparable for one default sort order, 2. Use Comparator for multiple or conditional sorts, 3. Use Comparator when you can't modify the source class, 4. Prefer Comparator in Java 8 with lambda and method references for cleaner, reusable code.
When working with sorting in Java, you’ll often come across two interfaces: Comparable and Comparator. They both allow objects to be compared, but they serve different purposes and are used in different contexts. Understanding the difference is key to writing clean, flexible, and maintainable code.
What is Comparable?
Comparable is used to define the natural ordering of a class. It’s part of the java.lang package and contains a single method: compareTo(T obj).
When a class implements Comparable, it means the objects of that class can be compared to each other in a default, logical way—like alphabetic order for strings or numerical order for integers.
Example:
public class Person implements Comparable<Person> {
private String name;
private int age;
// constructor, getters...
@Override
public int compareTo(Person other) {
return this.name.compareTo(other.name); // Natural order by name
}
}Now, you can sort a list of Person objects without any extra code:
List<Person> people = new ArrayList<>(); // add people... Collections.sort(people); // Uses natural ordering (by name)
? Use Comparable when there's an obvious, default way to sort the objects.
What is Comparator?
Comparator is more flexible. It’s defined in the java.util package and allows you to create custom comparison logic outside the class. You can have multiple comparators for different sorting needs (e.g., sort by age, by name, by salary).
You don’t modify the original class—instead, you define a separate comparison rule.
Example:
Comparator<Person> byAge = new Comparator<Person>() {
@Override
public int compare(Person p1, Person p2) {
return Integer.compare(p1.getAge(), p2.getAge());
}
};
// Or using lambda (Java 8 )
Comparator<Person> byAge = (p1, p2) -> Integer.compare(p1.getAge(), p2.getAge());Now sort using this custom rule:
Collections.sort(people, byAge);
You can even chain them:
Comparator<Person> byNameThenAge = Comparator.comparing(Person::getName)
.thenComparing(Person::getAge);? Use Comparator when:
- You want multiple sorting strategies
- You can’t modify the source class
- The natural order doesn’t make sense or isn’t desired
Key Differences at a Glance
| Feature | Comparable | Comparator |
|---|---|---|
| Package | java.lang.Comparable | java.util.Comparator |
| Method | int compareTo(T obj) | int compare(T o1, T o2) |
| Defines | Natural ordering | Custom ordering(s) |
| Implemented by | The class itself | External class or lambda |
| Number of sort orders | One (default) | Multiple (as needed) |
| Modifies original class? | Yes | No |
Practical Tips
- Default sort? → Use
Comparable - Need to sort differently in different situations? → Use
Comparator - Sorting third-party classes? → You must use
Comparator(can't modify the class) - Java 8 ? Take advantage of
Comparator.comparing()and method references for cleaner code.
For example:
people.sort(Comparator.comparing(Person::getAge).reversed());
This sorts people by age in descending order—concise and readable.
Basically, Comparable sets the default rule, while Comparator gives you the flexibility to break or change that rule when needed. Knowing when to use each makes your code more intuitive and reusable.
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