How to Sort Strings in Java

How to Sort a string in Java

A sequence of characters is referred to as a string. String objects are immutable in Java, meaning they can't be modified after being created. Although no string classes method is available for directly Sorting strings in Java, we may sort string array in Java by applying other methods one after the other. But first, we will see how we can operate over an immutable string in Java.

So, before we move on how to sort a string in Java, we first convert the given string into a character array using a string method -  toCharArray(),

Code

class SortString {
    public static void main(String[] args) {
        String str = "codingninjas";
        char arr[] = str.toCharArray();
        // Testing if the string converted into array is mutable now.
        arr[2] = 'T';
        System.out.print(arr);
    }
}

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Output

Let us see first what a lexicographically sorted string looks like:

Input String: codingninjas

Output String:  acdgiijnnnos

There are two ways we can sort string array in Java. They are:

1. With a User-defined method.
2. With the sort() method provided inside the Arrays class in Java.

Check this out, Fibonacci Series in Java, and Duck Number in Java.

Sorting strings in Java with user-defined methods

A string array can be sorted by comparing each element to the remainder. We've done the same thing in the following example. Two for-loops have been utilized. In comparison, the inner (second) for loop avoids repeats. If the condition (arr[i].compareTo(arr[j])>0 is true, the swapping and sorting of the array is performed.

Let us see an example of sorting strings in Java using a user-defined algorithm, bubble sort.

Code

import java.io.*; 
class SortString {
 
    // Main driver method
    public static void main(String[] args) throws Exception
    {
        // Custom string
        String str = "codingninjas";
       
        // Converting string into an array for operating
        char arr[] = str.toCharArray();
 
        // User-defined logic for sorting strings in java
        char temp;
        int i = 0;
        while (i < arr.length) {
            int j = i + 1;
            while (j < arr.length) {
                if (arr[j] < arr[i]) {
                   
                    // Comparing the characters one by one
                    temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                }
                j += 1;
            }
            i += 1;
        }
        System.out.println("Original String: "+ str);
        
		// Final sorted array
        System.out.println("Sorted String: "+ new String(arr));
    }
}

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Output

This sorting technique is known as bubble sort. We can use other user-defined sorting techniques such as Insertion Sort, Merge Sort, Radix Sort, etc.

Must Read Array of Objects in Java

Sorting strings in Java using Arrays.sort()

Arrays is a Java class that contains the sort() method for sorting an array in ascending order. It is part of the Java.util package. It sorts using the dual-pivot Quicksort algorithm. It has an O(n log(n)) complexity. It's a static method that takes an array as an argument but doesn't perform anything with it. We may use the class name to call it directly. It accepts int, float, double, long, char, and byte arrays. 

Let as see an example how to sort a string in java using Arrays.sort().

Code

import java.util.Arrays;
class SortString {
    public static void main(String[] args) {
        String str = "codingninjas";
        char arr[] = str.toCharArray();
        System.out.println("Original String: "+ str);
        
        // Sorting strings in Java using Arrays.sort()
        Arrays.sort(arr);
        System.out.println("Sorted String: "+ new String(arr));
    }
}

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Output

Note: The Java compiler sorts the character array based on the element's ASCII codes. Therefore, it will put the uppercase letters at the starting and the lower case alphabets later. To overcome this, we can compare the lowercase of each element while sorting strings in java using a custom method.

Also Read - Selection Sort in C

Frequently Asked Questions

Why do we need to convert a string into a character array?

Strings defined in Java are immutable, and we need to operate on them for sorting purposes, for which we need to convert them into characters array first.

How to sort a string in java in non-increasing order?

String or the converted character array can be sorted in descending order using the opposite logic used in the user-defined comparator.

What does the compare(char a, char b) function do and return?

public int compare(Object a, Object b) will return negative if a has to come before b, will return positive if a has to come after b, and return 0 if a is equal to b.

How to convert character array back to string?

 We can make a new string using string builder and append elements into it or convert it using the Arrays.toString() method.

What are the most famous sorting algorithms used in Java?

Here are the top five Java sorting algorithms:

• Merge Sort
• Heap Sort
• Insertion Sort
• Selection Sort
• Bubble Sort

Conclusion

In this article, we have intensively learned how to sort a string in Java with user-defined methods and the in-built Arrays.sort() method. We have more such articles on Java such as Wrapper classes, Multithreading in Java, exception handling in Java to enhance your knowledge in the field.

Array in Java

Recommended Problems - 

• String Args in Java
• Sort 0 1 2 
• Wiggle sort
• Find first and last position in sorted array

We hope that this blog has helped you enhance your knowledge of sorting strings in Java and if you'd like to learn more, check out our articles on Code Studio. 

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Happy coding!