Write a java program to reverse a string?

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

This method takes the first character of a string (str.charAt(0)) and puts it at the end of the string. And then calls itself on the remainder of the string (str.substring(1)). Finally adds these two things to get the reverse of the passed string (recursiveMethod(str.substring(1)) + str.charAt(0)). When the passed string is one character or less (str.length() <= 1), it stops calling itself and just returns the string passed.

If the “MyJava” is the string to reverse, then this method works like this.

1st Call —>   recursiveMethod(“MyJava”)
2nd Call —> recursiveMethod(“yJava”) + “M”
3rd Call —>  (recursiveMethod(“Java”) + “y”) + “M”
4th call —>  ((recursiveMethod(“ava”) + “J”)+”y”) + “M”
5th Call —>  (((recursiveMethod(“va”) + “a”) + “J”)+”y”) + “M”
6th Call —>  ((((recursiveMethod(“a”) + “v”) + “a”) + “J”)+”y”) + “M”

After 6th call, it Stops calling itself. Because the length of passed string is 1. So, finally it returns “avaJyM”.

Below is the Java program which reverses the string “MyJava” using all three above methods.

public class ReverseTheString
{
    public static void main(String[] args)
    {
        String str = "MyJava";
 
        //1. Using StringBuffer Class
 
        StringBuffer sbf = new StringBuffer(str);
 
        System.out.println(sbf.reverse());    //Output : avaJyM
 
        //2. Using iterative method
 
        char[] strArray = str.toCharArray();
 
        for (int i = strArray.length - 1; i >= 0; i--)
        {
            System.out.print(strArray[i]);    //Output : avaJyM
        }
 
        System.out.println();
 
        //3. Using Recursive Method
 
        System.out.println(recursiveMethod(str));    //Output : avaJyM
    }
 
    //Recursive method to reverse string
 
    static String recursiveMethod(String str)
    {
         if ((null == str) || (str.length() <= 1))
         {
                return str;
         }
 
         return recursiveMethod(str.substring(1)) + str.charAt(0);
    }
}