How To Sort An Array In Java – Tutorial With Examples

This Tutorial will Explain Various Methods to Sort An Array in Java in Ascending, Descending & Alphabetical Order with the help of Simple Examples:

Sorting arranges data in a specific order. Computer data consists of records made up of one or more fields. To use data efficiently and perform various operations like searching, accessing, etc. it is advisable that this data is arranged in some specific order.

For Example, if there are numerous records of student data, then we could arrange this data depending on the student id or student name. This is termed as sorting. Hence sorting is essential to use the data more efficiently and easily.

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Sort Arrays in Java

In Java, arrays contain data and we should sort this data to arrange it according to some criteria provided. In this tutorial, we will discuss the sorting of Arrays in detail along with simple examples.

How To Sort An Array In Java

Java provides the following methods to sort the arrays.

  • Using For Loops: You can use for loops to traverse the array and compare adjacent elements while traversing and putting them in order.
  • Using The Sort method: The Arrays class of  ‘java.util’ package provides the sort method that takes an array as an argument and sorts the array. This is a direct sorting method and you can sort an array with just one method call.

Let's explore both these methods in detail.

Using Loops

You can sort the array using manual sorting like using for loops. What you can do is use two for loops, one to traverse the array from the starting and another for loop inside the outer one to traverse the next element.

In the body, you compare the adjacent elements and swap if they are not in order. You can use a temporary variable for the swapping of elements.

The program below shows this approach.

public class Main {    
    public static void main(String[] args) {        
        //define original array     
        int [] intArray = new int [] {52,45,32,64,12,87,78,98,23,7};     
        int temp = 0;    

        //print original array    
       System.out.println("Original array: ");    
       for (int i = 0; i <intArray.length; i++) {     
           System.out.print(intArray[i] + " ");    
        }    
        //Sort the array in ascending order using two for loops    
        for (int i = 0; i <intArray.length; i++) {     
          for (int j = i+1; j <intArray.length; j++) {     
              if(intArray[i] >intArray[j]) {      //swap elements if not in order
                 temp = intArray[i];    
                 intArray[i] = intArray[j];    
                 intArray[j] = temp;    
               }     
            }     
        }    
        //print sorted array    
        System.out.println("\nArray sorted in ascending order: ");    
        for (int i = 0; i <intArray.length; i++) {     
            System.out.print(intArray[i] + " ");    
        }    
    }    
}    

Output:

Using loops

Sorting using for loop can be efficient when smaller arrays are involved. It can get complicated when the array size increases.

Sort Method

The sort method provided by ‘java.util.Arrays’ class is a very simple and faster way to sort an array. This method can sort elements of primitive types as well as objects that implement the comparable interface.

When primitive type elements are being sorted, the sort method uses quicksort. When objects are being sorted, iterative mergesort is used.

The general prototype of sort method is as follows:

Arrays.sort (T[] t_arr);

Here, T[] is the data type and t_arr is the array that is to be sorted.

The above prototype works for arrays implementing Comparable interface.

For arrays of custom objects, you can use another variant of Arrays.sort as given below.

Arrays.sort(T[] t_arr, Comparator.c);

So for the arrays that do not implement Comparable interface, a comparator should be passed in the sort function. Note that by default the sort method sorts the array in ascending order.

Let us see some specific examples of array sorting.

Sort Numeric Array In Ascending Order

The first demonstration is sorting of number array in ascending order using sort methods. As already mentioned, by default the sort method sorts the array in ascending order. Thus, to sort a numeric array in ascending order, you just have to call the method on the array in question.

Given below is an example to show this.

import java.util.Arrays; 

public class Main 
{ 
public static void main(String[] args) 
    { 
        //define an array
        int[] intArray = {52, 45, 32, 64, 12, 87, 78, 98, 23, 7}; 

        System.out.printf("Original Array : %s", Arrays.toString(intArray)); 

        Arrays.sort(intArray); 

        System.out.printf("\n\nSorted Array : %s", Arrays.toString(intArray)); 
    } 
}

Output:

Sort Numeric array in ascending order

In the above program, just one function call sorts the array in ascending order.

Sort Numeric Array In Descending Order

The next task is to sort the numeric array in descending order. To do this the sort method is provided with a second argument ‘Collections.reverseOrder ()’ that sorts an array in descending order.

Program to sort array in descending order is given below.

import java.util.Arrays; 
import java.util.Collections; 

public class Main 
{ 
    public static void main(String[] args) 
    { 
        //Collections.reverseOrder do not work for primitive Types 
        //define an array with Integer
        Integer[] IntArray = {52, 45, 32, 64, 12, 87, 78, 98, 23, 7};  

        //print original array
        System.out.printf("Original Array: %s", 
                 Arrays.toString(IntArray)); 

        // Sorts IntArray in descending order 
        Arrays.sort(IntArray, Collections.reverseOrder()); 

        //print sorted array  
        System.out.printf("\n\nSorted Array: %s", 
               Arrays.toString(IntArray)); 
    } 
}

Output:

Sort Numeric array in descending order

Sort String Array In Alphabetical Order

Just like numeric arrays, you can also sort string array using the sort function. When you pass the string array, the array is sorted in ascending alphabetical order. To sort the array in descending alphabetical order, you should provide the Collections interface method reverseOrder () as the second argument.

The following program demonstrates the sorting of a string array in ascending as well as descending order.

import java.util.Arrays; 
import java.util.Collections; 

public class Main 
{ 
    public static void main(String[] args) 
    { 
        String str_Array[] = {"Java", "Python", "Perl", "C++", "C#", "AS400"}; 

        System.out.printf("Original Array: \n%s\n\n", Arrays.toString(str_Array));

        // Sorts str_Array in ascending order 
        Arrays.sort(str_Array); 
        System.out.printf("Array sorted in ascending order: \n%s\n\n",                        
               Arrays.toString(str_Array)); 

        // Sorts str_Array in descending order 
        Arrays.sort(str_Array, Collections.reverseOrder()); 

        System.out.printf("Array sorted in descending order : \n%s\n\n", 
              Arrays.toString(str_Array)); 
    } 
}

Output:

Sort string array in alphabetical order

The output of the program shows a sorted array of strings in both ascending as well as descending order.

Frequently Asked Questions

Q #1) What is Sorting in Java?

Answer: Sorting refers to arranging data in order either alphabetically or numerically.

Q #2) Which Sorting technique is used in Arrays sort in Java?

Answer: Arrays use dual-pivot Quicksort for primitive data types and Mergesort for sorting objects.

Q #3) What is a Comparator in Java?

Answer: Comparator interface is a part of the java.util package and is used to arrange the user-defined objects. Comparator interface is mostly used during the sorting of objects using the sort method.

Q #4) What is the use of Sorting in Java?

Answer: Sorting is a technique of arranging data in a particular order. Sorting of data is useful as we can search for data more efficiently and quickly. We can also easily carry out other operations like accessing, storing, etc. on the ordered data.

Q #5) Is it possible to Sort lists in Java?

Answer: Yes. Lists are a part of the Collections interface in Java and we can use the sort() method of the Collections interface to sort the list.

Conclusion

This completes our discussion on the sorting of arrays in Java. We have discussed the various methods to sort arrays in Java including the ones provided by Java packages as well as the traditional method of using ‘for’ loops to sort array elements one by one.

We saw how to sort an array in ascending and descending order. Then we learned how to sort a string array in alphabetical order.

We will continue to explore more topics on arrays in Java in our subsequent tutorials.

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