Java Comparable Comparator — Free Java Tutorial

TL;DR: Learn Java Comparable Comparator in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Java Comparable Comparator in Java

Comparable<T> (java.lang.Comparable) defines the natural ordering of a class. Implement its compareTo(T other) method. Collections.sort() and Arrays.sort() use this.

Comparator<T> (java.util.Comparator) defines an external, custom ordering. Pass it to sort methods as a second argument. Multiple Comparators can exist for one class.

compareTo() convention: return negative if this < other, 0 if equal, positive if this > other. Use Integer.compare(a, b) rather than a - b to avoid overflow.

Java 8+ Comparator.comparing() creates Comparators from key extractors. Chain with .thenComparing() for multi-level sorting. .reversed() inverts order.

class Student implements Comparable<Student> {
    int marks;
    @Override
    public int compareTo(Student other) {
        return Integer.compare(this.marks, other.marks);
    }
}

Comparator<Student> byName = Comparator.comparing(s -> s.name);
Comparator<Student> byMarksDesc =
    Comparator.com

Learn Java Comparable Comparator step by step with Syllab's free interactive Java tutorial — runnable code examples, practice exercises and instant AI feedback, all free with no signup. Explore the full Java course →