Sorting and Searching Arrays in Java

Introduction

Sorting and searching are common operations performed on arrays in Java. Sorting arranges the elements of an array in a specific order, while searching finds the position of a particular element in the array.

Sorting Arrays

Arrays.sort() Method

The Arrays.sort() method is used to sort arrays in ascending order. For arrays of primitive types, it uses a modified quicksort algorithm. For arrays of objects, it uses the natural ordering of the elements or a specified comparator.

Example

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] numbers = {5, 2, 7, 1, 9};
        Arrays.sort(numbers);
        System.out.println(Arrays.toString(numbers)); // Outputs: [1, 2, 5, 7, 9]
    }
}

Sorting Arrays in Descending Order

To sort arrays in descending order, you can use the Comparator.reverseOrder() method along with Arrays.sort() for arrays of objects, or you can reverse the array after sorting for arrays of primitive types.

Example

import java.util.Arrays;
import java.util.Comparator;

public class Main {
    public static void main(String[] args) {
        Integer[] numbers = {5, 2, 7, 1, 9};
        Arrays.sort(numbers, Comparator.reverseOrder());
        System.out.println(Arrays.toString(numbers)); // Outputs: [9, 7, 5, 2, 1]
    }
}

Sorting Arrays of Objects

When sorting arrays of objects, the objects must implement the Comparable interface or you must provide a custom Comparator.

Example

import java.util.Arrays;
import java.util.Comparator;

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

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public int compareTo(Person other) {
        return Integer.compare(this.age, other.age);
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class Main {
    public static void main(String[] args) {
        Person[] people = {
                new Person("Alice", 25),
                new Person("Bob", 30),
                new Person("Charlie", 20)
        };

        Arrays.sort(people);
        System.out.println(Arrays.toString(people)); // Sorted by age
    }
}

Searching Arrays

Arrays.binarySearch() Method

The Arrays.binarySearch() method is used to search for a specified element in a sorted array. It returns the index of the element if found, otherwise it returns a negative value.

Example

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int index = Arrays.binarySearch(numbers, 5);
        System.out.println("Index of 5: " + index); // Outputs: 4
    }
}

Note

• The array must be sorted before using Arrays.binarySearch().
• If the element is not found, the method returns the insertion point (negative value).

Conclusion

Sorting and searching are essential operations performed on arrays in Java. The Arrays.sort() method is used to sort arrays, and Arrays.binarySearch() is used to search for elements in sorted arrays. Understanding these operations allows you to efficiently manage and manipulate array data in Java.