Arrays in Java

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Sorting Arrays

Arrays in Java Sorting Arrays

The Arrays.sort() method provides a convenient way to sort arrays of both primitive data types and objects. This method is part of the java.util.Arrays utility class and includes overloaded versions that handle different types of data and sorting needs.

Sorting Primitive Arrays

For arrays of primitive types (like int, double, char), Arrays.sort() sorts elements in ascending order by default. It uses a highly optimized algorithm for efficient sorting.

Example with an int array:

int[] numbers = {5, 1, 4, 2, 3};
Arrays.sort(numbers);
System.out.println(Arrays.toString(numbers)); // Output: [1, 2, 3, 4, 5]

This approach works for all primitive types (int, double, char, etc.) and is very fast, suitable for most applications.

Sorting Object Arrays

For arrays containing objects, Arrays.sort() also sorts in ascending order by default, based on the “natural order” of the elements. The objects must either implement the Comparable interface or a custom Comparator must be provided. Java classes like String and Integer implement Comparable by default.

Example with a String array:

String[] fruits = {"banana", "apple", "cherry"};
Arrays.sort(fruits);
System.out.println(Arrays.toString(fruits)); // Output: [apple, banana, cherry]

Sorting with Custom Comparators

If you need a different order (e.g., descending order), or are sorting based on a property of an object, you can use a Comparator.

Example with a custom comparator for descending order:

Integer[] numbers = {5, 1, 4, 2, 3};
Arrays.sort(numbers, Comparator.reverseOrder());
System.out.println(Arrays.toString(numbers)); // Output: [5, 4, 3, 2, 1]

Sorting Arrays of Custom Objects

For arrays of custom objects, create a Comparator to define the sort criteria or have your class implement Comparable.

Example with custom objects (e.g., sorting by age in a Person class):

class Person {
    String name;
    int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return name + " (" + age + ")";
    }
}

Person[] people = {
    new Person("Alice", 30),
    new Person("Bob", 25),
    new Person("Charlie", 20)
};

// Sort by age using a custom Comparator
Arrays.sort(people, Comparator.comparingInt(person -> person.age));
System.out.println(Arrays.toString(people)); // Output: [Charlie (20), Bob (25), Alice (30)]
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