How To Reverse A String In Java Using Recursion

In this article, we will see how to reverse a string in java using the recursion.

We have seen multiple ways to reverse a string in the previous article.

Now we will see how to reverse a string using the recursion.

A function to reverse the string using the recursion

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public static String reverse(String str) {
    if ((null == str) || (str.length() <= 1)) {
        return str;
    }
    return reverse(str.substring(1)) + str.charAt(0);
}

In the above method reverse() we are taking String str to be reversed.

We are checking if the str is null or its length is less than 1. If found, we will return the same string.

Then we are returning the following statement

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reverse(str.substring(1)) + str.charAt(0);

In the above statement we are calling the reverse() function again with str.substring(1) as parameter. And adding the character at 0th index.

So if we passed the “Hello” String to the function, the call will look like the code below.

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reverse("Hello")
(reverse("ello")) + "H"
((reverse("llo")) + "e") + "H"
(((reverse("lo")) + "l") + "e") + "H"
((((reverse("o")) + "l") + "l") + "e") + "H"
(((("o") + "l") + "l") + "e") + "H"
"olleH"

A complete Java Example

The full example java program is as given below.

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/**
 * A java program to reverse a striong using recursion.
 * 
 * @author gaurav
 *
 */
public class ReverseStringUsingRecursion {

	public static void main(String[] args) {
		String str = "hello";
		System.out.println(reverse(str));

	}

	public static String reverse(String str) {
	    if ((null == str) || (str.length() <= 1)) {
	        return str;
	    }
	    return reverse(str.substring(1)) + str.charAt(0);
	}
}

Output:

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olleh

The example java program given in the above tutorial can be found at this GitHub Gist.

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