Reverse a string in Java

Question

I have  Hello World  kept in a String variable named hi   I need to print it  but reversed   How can I do this  I understand there is some kind of a function already built-in into Java that does that   Related  Reverse each individual word of    Hello World    string with Java

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public String reverseWords String s         String reversedWords            if s length   lt  0            return reversedWords       else if s length      1           if s                      return                       return s             char arr     s toCharArray        int j   arr length-1      while j  gt   0            if  arr j                       reversedWords  arr j            else              String temp                 while j gt  0  amp  amp  arr j                           temp  arr j                   j--                            j                temp   reverseWord temp               reversedWords  temp                    j--              String   chk   reversedWords split            if chk    null    chk length    0           return                return reversedWords        public String reverseWord String s        char   arr   s toCharArray         for int i 0 j arr length-1 i lt  j i   j--           char tmp   arr i           arr i    arr j           arr j    tmp            return String valueOf arr

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For Online Judges problems that does not allow StringBuilder or StringBuffer  you can do it in place using char   as following   public static String reverse String input       char   in   input toCharArray        int begin 0      int end in length-1      char temp      while end gt begin           temp   in begin           in begin  in end           in end    temp          end--          begin              return new String in

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Sequence of characters  or  StringString s Family   String testString    Yashwanth 777       1 1 4 D80016  2          Using Java 8 Stream API   First we convert String into stream by using method CharSequence chars    then we use the method IntStream range to generate a sequential stream of numbers  Then we map this sequence of stream into String   public static String reverseString Stream String str        IntStream cahrStream   str chars        final int   array   cahrStream map  x - gt  x   toArray         int from   0  upTo   array length      IntFunction lt String gt  reverseMapper    i  - gt    Character toString  char  array   upTo - i     from - 1             String reverseString   IntStream range from  upTo     for  int i   from  i  lt  upTo   i                         mapToObj  reverseMapper                      array  lastElement                collect Collectors joining                   Joining stream of elements together into a String               toString                                     This object  which is already a string   is itself returned       System out println  Reverse Stream as String      reverseString       return reverseString         Using a Traditional for Loop   If you want to reverse the string then we need to follow these steps    Convert String into an Array of Characters  Iterate over an array in reverse order  append each Character to temporary string variable until the last character    public static String reverseString  String reverse         if  reverse    null  amp  amp  reverse        amp  amp  reverse length    gt  0              char   arr   reverse toCharArray            String temp               for  int i   arr length-1  i  gt   0  i--                 temp    arr i                     System out println  Reverse String      temp             return null         Easy way to Use reverse method provided form StringBuffer or StringBuilder Classes    StringBuilder and StringBuffer are mutable sequence of characters  That means one can change the value of these object s    StringBuffer buffer   new StringBuffer str   System out println  StringBuffer - reverse      buffer reverse       String builderString    new StringBuilder str   reverse   toString  System out println  StringBuilder generated reverse String      builderString       StringBuffer has the same methods as the StringBuilder  but each method in StringBuffer is synchronized so it is thread safe

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1  Using Character Array   public String reverseString String inputString        char   inputStringArray   inputString toCharArray        String reverseString           for  int i   inputStringArray length - 1  i  gt   0  i--            reverseString    inputStringArray i             return reverseString      2  Using StringBuilder   public String reverseString String inputString        StringBuilder stringBuilder   new StringBuilder inputString       stringBuilder   stringBuilder reverse        return stringBuilder toString        OR  return new StringBuilder inputString  reverse   toString

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Procedure    We can use split   to split the string  Then use reverse loop and add the characters     Code snippet   class test     public static void main String args               String str    world         String   split  str split             String revers             for  int i   split length-1  i gt  0  i--                  revers    split i                 System out printf   s   revers                output   dlrow

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public static String revString String str       char   revCharArr   str toCharArray        for  int i 0  i lt  str length   2  i             char f   revCharArr i           char l   revCharArr str length  -i-1           revCharArr i    l          revCharArr str length  -i-1    f            String revStr   new String revCharArr       return revStr

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One natural way to reverse a String is to use a StringTokenizer and a stack  Stack is a class that implements an easy-to-use last-in  first-out  LIFO  stack of objects   String s    Hello My name is Sufiyan     Put it in the stack frontwards  Stack lt String gt  myStack   new Stack lt  gt     StringTokenizer st   new StringTokenizer s   while  st hasMoreTokens           myStack push st nextToken         Print the stack backwards  System out print       s           backwards by word is  n t      while   myStack empty        System out print myStack pop       System out print          System out println

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public class StringReverse1    public static void main String   args        String name    quot Vaquar khan quot        char array     name toCharArray        System out println name       System out println reverseString array       private static String reverseString char   array        String reverse    quot  quot               for  int i   array length - 1  i  gt   0  i--              System out println array i                       reverse    array i             return reverse        Results         Vaquar khan        nahk rauqaV

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Just another method private void revByFor                 String str  quot google quot               StringBuilder revStr  new StringBuilder                char   str1  str toCharArray                for  char c   str1                    revStr insert 0  c                                 System out println revStr

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You can also try this   public class StringReverse       public static void main String   args            String str    Dogs hates cats           StringBuffer sb   new StringBuffer str           System out println sb reverse

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package logicprogram  import java io     public class Strinrevers   public static void main String args   throws IOException       BufferedReader br new BufferedReader new InputStreamReader System in        System out println  enter data        String data br readLine        System out println data       String str         char cha   data toCharArray         int l data length        int k l-1      System out println l         for int i 0 k gt  i k--                 str  cha k                 String text String valueOf ch       System out println str

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All above solution is too good but here I am making reverse string using recursive programming    This is helpful for who is looking recursive way of doing reverse string    public class ReversString    public static void main String args          char s      Dhiral Pandya  toCharArray        String r   new String reverse 0  s        System out println r      public static char   reverse int i  char source           if  source length   2    i            return source             char t   source i       source i    source source length - 1 - i       source source length - 1 - i    t       i        return reverse i  source

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System out print  Please enter your name      String name   keyboard nextLine     String reverse   new StringBuffer name  reverse   toString    String rev   reverse toLowerCase    System out println rev     I used this method to turn names backwards and into lower case

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public static void reverseString String s           System out println  ---------            for int i s length  -1  i gt  0 i--               System out print s charAt i                          System out println

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Take a look at the Java 6 API under StringBuffer  String s    sample   String result   new StringBuffer s  reverse   toString

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Having surrogate pairs in input string  you have to leave them not reversed  so good and generic way of reversing the string is using StringBuilder reverse as it handles extended character set correctly  So called supplementary characters consisting of surrogate pairs are unicode values up to U 10FFFF encoded as two consecutive chars   Here is my solution   String aString    abcdef   String reversedString   aString         codePoints           boxed           map Character  toString          collect Collectors collectingAndThen Collectors toList    aList - gt               Collections reverse aList              return String join     aList                  String codepoints returns stream of integers surrogate pair  double chars  packed in one integer  this is different that String chars for which one integer   one char as of Java 11 Character toString also accepts codepoint  and returns either String of length 1 or 2 if there is surrogate pair

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public void reverString    System out println  Enter value    BufferedReader br new BufferedReader new InputStreamReader System in     try     String str br readLine      char   charArray str toCharArray      for int i charArray length-1  i gt  0  i--      System out println charArray i               catch IOException ex

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You can use a for statement too         for  int y   0  y  lt  phrase length    y--         char ch   phrase charAt y-1         System out print ch

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It is very simple in minimum code of lines  public class ReverseString       public static void main String   args            String s1    neelendra           for int i s1 length  -1 i gt  0 i--                                System out print s1 charAt i

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You can use this   new StringBuilder hi  reverse   toString     Or  for versions earlier than JDK 1 5  use java util StringBuffer instead of StringBuilder     they have the same API  Thanks commentators for pointing out that StringBuilder is preferred nowadays when there is no concurrency concern

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There are many ways to reverse a string   1  Converting String into Bytes  getBytes   method is used to convert the input string into bytes     import java lang    import java io    import java util    class ReverseString  public static void main String   args        String input    GeeksforGeeks       byte    strAsByteArray   input getBytes        byte    result    new byte  strAsByteArray length        for  int i   0  i lt strAsByteArray length  i            result i              strAsByteArray strAsByteArray length-i-1        System out println new String result          2 Converting String to character array  The user input the string to be reversed   Personally suggested   import java lang    import java io    import java util      class ReverseString  public static void main String   args        String input    GeeksForGeeks           convert String to character array        by using toCharArray     char   try1   input toCharArray         for  int i   try1 length-1  i gt  0  i--          System out print try1 i          3 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 LinkedList object which is a type of list of characters   import java lang    import java io    import java util      class ReverseString   public static void main String   args        String input    Geeks For Geeks       char   hello   input toCharArray        List lt Character gt  trial1   new ArrayList lt  gt          for  char c  hello          trial1 add c        Collections reverse trial1       ListIterator li   trial1 listIterator        while  li hasNext            System out print li next

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public static String reverseIt String source        int i  len   source length        StringBuilder dest   new StringBuilder len        for  i    len - 1   i  gt   0  i--           dest append source charAt i               return dest toString        http   www java2s com Code Java Language-Basics ReverseStringTest htm

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It gets the value you typed and returns it reversed     public static  String reverse  String a       char   rarray   a toCharArray        String finalvalue           for  int i   0  i  lt  rarray length  i                  finalvalue    rarray rarray length - 1 - i            return finalvalue

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Maybe using new StringBuilder str  reverse toString   is convenient and efficient enough  But if you wanna do it yourself  try this one   public static String reverse String str        StringBuilder sb   new StringBuilder str length         for  int i   str length   - 1  i  gt   0  i--            sb append str charAt i              return sb toString        Some answers use str toCharArray   to get this string s char array  this will result to allocate new memory to store these chars  which is not efficient     StringBuffer is thread safe  but StringBuilder is not  So StringBuffer is less efficient than StringBuilder  If not necessary  use  StringBuilder is a better practice

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As others have pointed out the preferred way is to use   new StringBuilder hi  reverse   toString     But if you want to implement this by yourself  I m afraid that the rest of responses have flaws   The reason is that String represents a list of Unicode points  encoded in a char   array according to the variable-length encoding  UTF-16    This means some code points use a single element of the array  one code unit  but others use two of them  so there might be pairs of characters that must be treated as a single unit  consecutive  high  and  low  surrogates    public static String reverseString String s        char   chars   new char s length         boolean twoCharCodepoint   false      for  int i   0  i  lt  s length    i              chars s length   - 1 - i    s charAt i           if  twoCharCodepoint                swap chars  s length   - 1 - i  s length   - i                     twoCharCodepoint    Character isBmpCodePoint s codePointAt i              return new String chars      private static void swap char   array  int i  int j        char temp   array i       array i    array j       array j    temp     public static void main String   args  throws Exception       FileOutputStream fos   new FileOutputStream  C  temp reverse-string txt        StringBuilder sb   new StringBuilder  Linear B Syllable B008 A          sb appendCodePoint 65536     http   unicode-table com es  10000     sb append           fos write sb toString   getBytes  UTF-16         fos write   n  getBytes  UTF-16         fos write reverseString sb toString    getBytes  UTF-16

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import java util Scanner   public class Test        public static void main String   args           Scanner input   new Scanner  System in           String word   input next            String reverse               for int i word length  -1  i gt  0  i--              reverse    word charAt i           System out println reverse                     If you want to use a simple for loop

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recursion    public String stringReverse String string        if  string    null    string length      0            return string            return stringReverse string substring 1     string charAt 0

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Solution  1 -- Using array and charAt       String name    reverse     String to reverse     Character   nameChar    new Character name length        Declaring a character array with length as length of the String which you want to reverse      for int i 0 i lt name length   i      this will loop you through the String     nameChar i  name charAt name length  -1-i     Using built in charAt   we can fetch the character at a given index       for char nam nameChar    Just to print the above nameChar character Array using an enhanced for loop     System out print nam           Solution  2 - Using StringBuffer and reverse         StringBuffer reverseString   new StringBuffer  reverse        System out println reverseString reverse       reverse    Causes the character sequence to be replaced by the reverse of the sequence

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Here is a low level solution   import java util Scanner   public class class1        public static void main String   args            Scanner in   new Scanner System in           String inpStr   in nextLine            System out println  Original String      inpStr           char temp          char   arr   inpStr toCharArray            int len   arr length          for int i 0  i lt  inpStr length    2  i   len--               temp   arr i               arr i    arr len-1               arr len-1    temp                     System out println  Reverse String      String valueOf arr

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Here is the code that can be used to reverse a String   public static void main String   args             String aString    noun            int size   aString length            String reversed                for  int i size-1 i gt  0 i--               reversed   reversed  aString charAt i               if  i    0                  System out println reversed                 you can also watch the video to better understand the concepts that are needed  https   www youtube com watch v KaoA0o2Tfi4

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This did the trick for me  public static void main String   args         String text    abcdefghijklmnopqrstuvwxyz        for  int i    text length   - 1   i  gt   0  i--            System out print text charAt i

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Since the below method  using XOR  to reverse a string is not listed  I am attaching this method to reverse a string   The Algorithm is based on       1  A XOR B  XOR B   A       2  A XOR B  XOR A   B   Code snippet   public class ReverseUsingXOR       public static void main String   args            String str    prateek           reverseUsingXOR str toCharArray                     Example         str  prateek         str low  p         str high  k         str low  p k         str high   p k  k  p         str low   p k  p k                        public static void reverseUsingXOR char   str            int low   0          int high   str length - 1           while  low  lt  high                str low     char   str low    str high                str high     char   str low    str high                   str low     char   str low    str high                low                high--                       display reversed string         for  int i   0  i  lt  str length  i                  System out print str i                         Output   keetarp

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Simple For loop in java   public void reverseString char   s        int length   s length      for  int i   0  i  lt  s length   2  i                 swaping character         char temp   s length - i - 1           s length - i - 1    s i           s i    temp

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public String reverse String s             String reversedString               for int i s length    i gt 0  i--                reversedString    s charAt i-1                         return reversedString

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Everybody proposes a way to reverse string here  If you  the reader of   the answer  are interested in  my way using  u202E unicode is here    public static String reverse String s            return   u202E    s      It can be tested from here   It is just to print  If your aim is to pass a string in a reversed manner  you need to do it using loop or recursion

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public static void main String   args        String str    Prashant       int len   str length        char   c   new char len       for  int j   len - 1  i   0  j  gt   0  j--  i              c i    str charAt j             str   String copyValueOf c       System out println str

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package ThingsInArray   public class MagicWithSelectionSort        public static void main String   arg            isSort  uhsnamiH               private static void isSort String name            String revName             for  int i   name toCharArray   length-1  i  gt 0   i--                revName revName name charAt i                     System out println revName

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String string  whatever   String reverse   new StringBuffer string  reverse   toString    System out println reverse

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StringBuilder s   new StringBuilder  racecar        for  int i   0  j   s length   - 1  i  lt   s length   2   i    j--            char temp   s charAt i           s setCharAt i  s charAt j            s setCharAt j  temp              System out println s toString

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import java util Scanner  public class StringReverseExample       public static void main String   args                String str rev          Scanner in   new Scanner System in           System out print  Enter the string               str   in nextLine            rev   new StringBuffer str  reverse   toString            System out println   nString before reverse   str           System out println  String after reverse   rev              Output    Enter the string   satyam  String before reverse satyam String after reverse maytas

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Here is an example using recursion   public void reverseString         String alphabet    ABCDEFGHIJKLMNOPQRSTUVWXYZ       String reverseAlphabet   reverse alphabet  alphabet length  -1      String reverse String stringToReverse  int index       if index    0           return stringToReverse charAt 0                   char letter   stringToReverse charAt index       return letter   reverse stringToReverse  index-1

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I tried  just for fun  by using a Stack  Here my code   public String reverseString String s        Stack lt Character gt  stack   new Stack lt  gt         StringBuilder sb   new StringBuilder        for  int i   0  i  lt  s length    i              stack push s charAt i              while   stack empty              sb append stack pop               return sb toString

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Just For Fun     Algorithm  str len     char reversedStr    new reversedStr len    Traverse i from 0 to len 2 and then     reversedStr i  str len-1-i        reversedStr len-1 i  str i    return reversedStr   Time Complexity O n  Space Complexity  O n   public class Reverse       static char reversedStr            public static void main String   args            System out println reversestr  quot jatin quot                       private static String reversestr String str            int strlen   str length            reversedStr   new char strlen                    for  int i   0  i  lt   strlen   2  i                  reversedStr i    str charAt strlen - 1 - i               reversedStr strlen - 1 - i    str charAt i                      return new String reversedStr

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public class Test    public static void main String args         StringBuffer buffer   new StringBuffer  Game Plan       buffer reverse       System out println buffer

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I am doing this by using the following two ways   Reverse string by CHARACTERS   public static void main String   args           Using traditional approach     String result         for int i string length  -1  i gt  0  i--            result   result   string charAt i             System out println result           Using StringBuffer class     StringBuffer buffer   new StringBuffer string       System out println buffer reverse             Reverse string by WORDS   public static void reverseStringByWords String string        StringBuilder stringBuilder   new StringBuilder        String   words   string split            for  int j   words length-1  j  gt   0  j--            stringBuilder append words j   append                 System out println  Reverse words      stringBuilder

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Without Using Arrays  you can store the Characters and concatenate them in reverse order   public static String reverseString String inpt         String sb           for int i   inpt length  -1  i gt  0  i--             sb   sb concat    inpt charAt i               return sb

[java] Reverse a string in Java

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