string-reverse

Recommended: Please try your approach on {IDE} first, before moving on to the solution.
Prerequisite: String vs StringBuilder vs StringBuffer in Java
Following are some interesting facts about String and StringBuilder classes :
1. Objects of String are immutable.
2. String class in Java does not have reverse() method, however StringBuilder class has built in reverse() method.
3. StringBuilder class do not have toCharArray() method, while String class does have toCharArray() method.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.
Converting String into Bytes: getBytes() method is used to convert the input string into bytes[].
Method:

1. Create a temporary byte[] of length equal
to the length of the input string.
2. Store the bytes (which we get by using
getBytes() method) in reverse order into
the temporary byte[] .
3. Create a new String abject using byte[] to
store result.

// Java program to ReverseString using ByteArray.
import java.lang.*;
import java.io.*;
import java.util.*;

// Class of ReverseString
class ReverseString {
public static void main(String[] args)
{
String input = "PrutordotAi";

// getBytes() method to convert string
// into bytes[].
byte[] strAsByteArray = input.getBytes();

byte[] result = new byte[strAsByteArray.length];

// Store result in reverse order into the
// result byte[]
for (int i = 0; i < strAsByteArray.length; i++)
result[i] = strAsByteArray[strAsByteArray.length - i - 1];

System.out.println(new String(result));
}
}
Output:

iA.roturP
Using built in reverse() method of the StringBuilder class: String class does not have reverse() method, we need to convert the input string to StringBuilder, which is achieved by using the append method of StringBuilder. After that, print out the characters of the reversed string by scanning from the first till the last index.

// Java program to ReverseString using StringBuilder
import java.lang.*;
import java.io.*;
import java.util.*;

// Class of ReverseString
class ReverseString {
public static void main(String[] args)
{
String input = "Prutor dot Ai";

StringBuilder input1 = new StringBuilder();

// append a string into StringBuilder input1
input1.append(input);

// reverse StringBuilder input1
input1.reverse();

// print reversed String
System.out.println(input1);
}
}
Output:

iA tod roturP
Converting String to character array: The user input the string to be reversed.
Method:
1. First, convert String to character array
by using the built in Java String class
method toCharArray().
2. Then, scan the string from end to start,
and print the character one by one.

// Java program to Reverse a String by
// converting string to characters one
// by one
import java.lang.*;
import java.io.*;
import java.util.*;

// Class of ReverseString
class ReverseString {
public static void main(String[] args)
{
String input = "PrutordotAi";

// convert String to character array
// by using toCharArray
char[] try1 = input.toCharArray();

for (int i = try1.length - 1; i >= 0; i--)
System.out.print(try1[i]);
}
}
Output:

iA.roturP
Convert the input string into character array by using the toCharArray(): Convert the input string into character array by using the toCharArray() – built in method of the String Class. Then, scan the character array from both sides i.e from the start index (left) as well as from last index(right) simultaneously.
1. Set the left index equal to 0 and right
index equal to the length of the string -1.
2. Swap the characters of the start index
scanning with the last index scanning
one by one. After that, increase the left
index by 1 (left++) and decrease the right
by 1 i.e., (right--) to move on to the next
characters in the character array .
3. Continue till left is less than or equal to
the right.

// Java program to Reverse a String using swapping
// of variables
import java.lang.*;
import java.io.*;
import java.util.*;

// Class of ReverseString
class ReverseString {
public static void main(String[] args)
{
String input = "Prutor Dot AI";
char[] temparray = input.toCharArray();
int left, right = 0;
right = temparray.length - 1;

for (left = 0; left < right; left++, right--) {
// Swap values of left and right
char temp = temparray[left];
temparray[left] = temparray[right];
temparray[right] = temp;
}

for (char c : temparray)
System.out.print(c);
System.out.println();
}
}
Output:

IA toD roturP

Using ArrayList object: Convert the input string into the character array by using toCharArray() built in method. Then, add the characters of the array into the ArrayList object. Java also has built in reverse() method for the Collections class. Since Collections class reverse() method takes a list object, to reverse the list, we will pass the ArrayList object which is a type of list of characters.
1. We copy String contents to an object
of ArrayList.
1. We create a ListIterator object by using
the listIterator() method on the ArrayList
object.
2. ListIterator object is used to iterate over
the list.
3. ListIterator object helps us to iterate
over the reversed list and print it one
by one to the output screen.

// Java program to Reverse a String using ListIterator
import java.lang.*;
import java.io.*;
import java.util.*;

// Class of ReverseString
class ReverseString {
public static void main(String[] args)
{
String input = "Prutor Dot AI";
char[] hello = input.toCharArray();
List<Character> trial1 = new ArrayList<>();

for (char c : hello)
trial1.add(c);

Collections.reverse(trial1);
ListIterator li = trial1.listIterator();
while (li.hasNext())
System.out.print(li.next());
}
}
Output:

IA toD roturP

Using StringBuffer: String class does not have reverse() method, we need to convert the input string to StringBuffer, which is achieved by using the reverse method of StringBuffer.

// Java program to demonstrate conversion from
// String to StringBuffer and reverse of string
import java.lang.*;
import java.io.*;
import java.util.*;

public class Test {
public static void main(String[] args)
{
String str = "Prutor";

// conversion from String object to StringBuffer
StringBuffer sbr = new StringBuffer(str);
// To reverse the string
sbr.reverse();
System.out.println(sbr);
}
}
Output:

roturP