5 Ways To Reverse A String In Java With Example

In this tutorial we will discuss  how to reverse a string in java . Although there are many ways to get the solution but we are sharing 5 different ways to  reverse a string. This question is frequently asked in the technical interview of java.This question is easy , but please mark this question in your to do list before attending any technical interview in java. First we will understand the question by writing example.

Input :   malayalam
Output: malayalam

Input : akbar
Output : rabka

Points to Keep in Mind Before attempting the Solution:

1. String class in java do not have reverse() method , StringBuilder class does have built in reverse() method.
2. StringBuilder class do not have toCharArray() method , while String class does have toCharArray() method.

Pseudo Code for Reverse String Method 1:

1. The user will input the string to be reversed.
2. First we will convert String to character array by using the built in java String class method toCharArray().

3. Then , we will scan the string from end  to start,  and print the character one by one.

import java.io.*;
import java.util.*;

public class reverseString {
    public static void main(String[] args) {
        String input="";
        System.out.println("Enter the input string");
        try
        {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            input = br.readLine();
            char[] try1= input.toCharArray();
            for (int i=try1.length-1;i>=0;i--)
            System.out.print(try1[i]);
        }
        catch (IOException e) {
            e.printStackTrace();
        }
}}

Pseudo Code for Reverse String Method 2:

1.  In the second method , we will use the built in reverse() method of the StringBuilder class ,.
Note :  String class does not have reverse() method . So we need to convert the input string to StringBuilder , which is achieved by using the append method of the StringBuilder.

2.  After that print out the characters of the reversed string  by scanning from the first till the last index.

import java.io.*;
import java.util.*;

public class reverseString {
 public static void main(String[] args) {
  String input="AliveisAwesome";
  StringBuilder input1 = new StringBuilder();
  input1.append(input);
  input1=input1.reverse(); 
  for (int i=0;i<input1.length();i++)
  System.out.print(input1.charAt(i));  
 }}
  

Pseudo Code for Reverse String Method 3:

1. Convert the input string into character array by using the toCharArray() built in method of the String Class .
2. In this method we will scan the character array from both sides , that is from the start index (left) as well as from last index(right) simultaneously.
3. Set the left index equal to 0 and right index equal to the length of the string -1.
4. 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 .
5. Continue till left is less than or equal to the right .

import java.io.*;
import java.util.*;

public class reverseString {
 public static void main(String[] args) {
    String input = "Be in present";
    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();
   }}
  

Pseudo Code for Reverse String Method  4:

1. Convert the input string into the character array by using toCharArray() built in method.

2. Then add the characters of the array into the LinkedList object . We used LinkedList because it maintains the insertion order of the input values.
3. 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 LinkedList object which is a type of list of characters.
4. We will create the ListIterator object by using the listIterator() method on the LinkedList object.
ListIterator object is used to iterate over the list.
5. ListIterator object will help us to iterate over the reversed list and print it one by one to the output screen.

import java.io.*;
import java.util.*;

public class reverseString {
 public static void main(String[] args) {
     String input = "Be in present";
     char[] hello=input.toCharArray();
     List<Character> trial1= new LinkedList<>();
     for(char c: hello)
     trial1.add(c);
     Collections.reverse(trial1);
     ListIterator li = trial1.listIterator();  
     while(li.hasNext())
    {System.out.print(li.next());}  
   }}
  

Pseudo Code for Reverse String Method 5 :

1. The last method is converting string into bytes .  getBytes()  method  is used to convert the input string into bytes[].
2. Then we will create a temporary byte[]  of length equal to the length of the input string.
3. We will store the bytes(which we get by using getBytes() method) in reverse order   into the temporary byte[] .

package ctci;
import java.io.*;
import java.util.*;

public class reverseString {
 public static void main(String[] args) {
  String input = "Be in present";
  byte [] strAsByteArray = input.getBytes();
  byte [] result = new byte [strAsByteArray.length];
   
  for(int i = 0; i<strAsByteArray.length; i++){
  result[i] = strAsByteArray[strAsByteArray.length-i-1];
  }
  System.out.println( new String(result));
   }}

Computer Hacking In The New Age, All You Need To Know About Hacking Today

Every human discovery has pros and cons, so is the computer which has pervaded all our lives. The modern humanity is increasingly dependent on computer for various day-to-day activities. Computers do us a whole lot of good things, but it is not without some pitfalls. With the extensive use of internet for hundreds of our needs, computer opens a vicious cycle of hackers. Computer hacking is a term which refers to an individual’s illegal and unauthorized access to the data which are stored in a user’s system. This is done to disturb the confidentiality and security of the user’s computer.

The hackers focus on individuals’ computer system when they are online. As long as you are not connected to internet you are less prone to hacking. The access to internet has actually made computer hacking easy. You must protect your computer with strong antivirus and firewall programs to keep hackers away. Hackers are known for creating problems which are difficult to solve. This gives a good business to computer investigators and technicians. Hacking can be done in lots of ways. Few of them are given below:

• Worms: These are the programs which propagate through networks.
• Trojans: These are hidden in websites, attached files and emails.
• Viruses: These attach themselves to various kinds of files. They can damage certain functions of your computer.

Hackers also crash on wireless networks which do not have firewall installed and enabled. They can also send email attachments with malicious software which get embedded on the victim’s computer. Hackers attack accounts which have weak passwords. All these are done to get access to confidential and sensitive information of the users. Whatever is the method of hacking, the effect is harmful for the user. Your system will be flooded with viruses, malwares which steal your information. In order to avoid hacking one has to make sure that the systems at home or office have the latest anti-virus program and firewall installed and enabled. These programs need to be regularly updated. Use the latest browser and scan your computer on a regular basis.

New Age...

The New Age of internet has brought with it many risk factors along with umpteen advantages. The New Age is the time where our personal lives are no longer very personal, but people are able to access personal information of internet users from various sources in the virtual world. We need to be careful about usernames and passwords, else it will lead to dangerous consequences. Universities, large companies and government agencies are mostly targeted by hackers simply because of the bulk of information they handle. The great newspapers like The Wall Street Journal and The New York Times were also targeted by hackers.

Computer hackers are people who gain remote access to information stored in a system elsewhere. During the 1950s and 60s hackers were more drawn towards learning the operations of a computer rather than stealing confidential information of a remote user. Unlike the olden days, now computer hacking has become more sophisticated and organized. In the late 1990s hackers tried to get access to files in the network of Pentagon. Some more expert hackers gained access to the patent files at the Indiana University School of Medicine in February 2003. Many hackers were sentenced in the history since hacking represents a potential national security threat.

Viruses

One major tool hackers use to steal information from computer systems is the use of viruses. Over the years the number of viruses has increased drastically. The virtual world now has above 100000 viruses and the number grows virtually every day. Apart from the threat the computer hackers pose, they also can be beneficial in one way. They can bring to light the flaws in a computer network. Hackers can help in redesigning the system and in making information inaccessible to illegal users and to unauthorized access.

Getting Administrative Access

Getting a log in password is one of the predominant ways to get access to a computer which is by the side of the hacker. Getting remote access to a computer is another way to hack a system. Managing to crack a Wi-Fi password is the third method of sneaking into someone else’s system. Hacking if done on a public or school computer will have serious consequences. The hacker will be put behind the bars for illegally accessing the computer which does not belong to him or her.