What is the most efficient algorithm for reversing

Question

What is the most efficient way to reverse a string in Java? Should I use some sort of xor operator? The easy way would be to put all the chars in a stack and put them back into a string again but I doubt that's a very efficient way to do it.

And please do not tell me to use some built in function in Java. I am interested in learning how to do it not to use an efficient function but not knowing why it's efficient or how it's built up.

Answer 1

public static String reverseString(String str)
{
    StringBuilder sb = new StringBuilder();

    for (int i = str.length() - 1; i >= 0; i--)
    {
        sb.append(str[i]);
    }

    return sb.toString();
}

Answer 2

An old post & question, however still did not see answers pertaining to recursion. Recursive method reverse the given string s, without relaying on inbuilt jdk functions

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

`

Answer 3

Using String:

String abc = "abcd";
int a= abc.length();

String reverse="";

for (int i=a-1;i>=0 ;i--)
{
    reverse= reverse + abc.charAt(i);
}
System.out.println("Reverse of String abcd using invert array is :"+reverse);

Using StringBuilder:

    String abc = "abcd";
    int a= abc.length();
    StringBuilder sb1 = new StringBuilder();

    for (int i=a-1;i>=0 ;i--)
    {
        sb1= sb1.append(abc.charAt(i));
    }
    System.out.println("Reverse of String abcd using StringBuilder is :"+sb1);