Printing reverse of any String without using any predefined function

Question

How to print the reverse of the String java is object orientated language without using any predefined function like reverse

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private void rev         String st  hello       String b          for int i st length  -1 i gt  0 i--           b b st charAt i              System out println  reverse     b

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You can do it either recursively or iteratively  looping    Iteratively    static String reverseMe String s       StringBuilder sb   new StringBuilder       for int i   s length   - 1  i  gt   0  --i       sb append s charAt i       return sb toString         Recursively    static String reverseMe String s       if s length      0       return        return s charAt s length   - 1    reverseMe s substring 0 s length  -1

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public class MyStack      private int maxSize     private char   stackArray     private int top     public MyStack int s          maxSize   s        stackArray   new char maxSize         top   -1          public void push char j          stackArray   top    j          public char pop           return stackArray top--           public char peek           return stackArray top           public boolean isEmpty           return  top    -1           public boolean isFull           return  top    maxSize - 1           public static void main String   args          MyStack theStack   new MyStack 10         String s  abcd         for int i 0 i lt s length   i          theStack push s charAt i          for int i 0 i lt s length   i          System out println theStack pop

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First of all  Why reinvent the wheel   That being said  Loop from the length of the string to 0 and concatenate into another string

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I had this a while back  and having answered with the obvious StringBuffer reverse   answer  they then asked  Can you reverse a char array without using those API methods and achieve the result without spooling into a new char array      At the time I recognised that I only needed to iterate over half the length of the char array  but made a bit of a hash of explaining the actual code that needed to go into it  it was a verbal question    Anyway  I tried it when I got home and came up with this   public class StringReverse    public static void main String   args        String a    String        char   aChar   a toCharArray         for  int i    aChar length-1  2   i  gt   0   i--           int posA   i          int posB    aChar length-1-i           char tmpA   aChar posA           char tmpB   aChar posB           System out println  Setting     posA     to     tmpB           System out println  Setting     posB     to     tmpA            aChar posA    tmpB          aChar posB    tmpA             System out println aChar          You can obviously achieve this with less code  but I think the temporary assignments in the method make it more clear what the code is doing   Outputs something like   Setting 2 to i Setting 3 to r Setting 1 to n Setting 4 to t Setting 0 to g Setting 5 to S  gnirtS   More of an interview question than a homework question  I d say

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Here s a recursive solution that just prints the string in reverse order  It should be educational if you re trying to learn recursion  I ve also made it  wrong  by actually having 2 print statements  one of them should be commented out  Try to figure out which mentally  or just run experiments  Either way  learn from it   static void printReverse String s        if   s isEmpty              System out print s substring 0  1            printReverse s substring 1            System out print s substring 0  1              Bonus points if you answer these questions    What is its stack requirement  Is it prone to stack overflow  Is it a tail recursion

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public class ReverseString    public static void main String   args         reverseString  HELLO       public static String reverseString String s       char   arr s toCharArray        for int i   arr length -1 i gt  0 i--           System out print arr i              String str String copyValueOf arr       return str

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This is the simplest solution   System out print  egaugnal detatneiro tcejbo si avaj

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String a  Siva    for int i 0 i lt  a length  -1 i         System out print a charAt i       for int i   a length   - 1  i  gt   0  --i       System out println a charAt i

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String reverse String s      int legnth   s length      char   arrayCh   s toCharArray      for int i 0  i lt  length 2  i            char ch   s charAt i         arrayCh i    arrayCh legnth-1-i         arrayCh legnth-1-i    ch        return new String arrayCh

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public class ReverseString    public static void main String    args         String s    reverse string        String b                    for  int i   0  i  lt  s length    i                       b  b   s substring s length  -1-i  s length  -i                                     System out println b

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public static void main String   args          String str    hello world here I am        StringTokenizer strToken   new StringTokenizer str       int token   strToken countTokens        String str1      new String token        char chr     new char str length         int counter   0       for int j 0  j  lt  str length    j               if str charAt j                        chr j    str charAt j            else               str1 counter      new String chr  trim                chr   new char str length                         str1 counter      new String chr  trim         for int i str1 length-1  i  gt   0   i--            System out println str1 i              O P is  am I here world hello

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package com ofs   public class ReverseWordsInString  public static void main String   args         String str    welcome to the new world and how are you feeling             Get the Java runtime     Runtime runtime   Runtime getRuntime           Run the garbage collector     runtime gc           Calculate the used memory     long firstUsageMemory   runtime totalMemory   - runtime freeMemory        System out println  Used memory in bytes      firstUsageMemory       System out println str       str   new StringBuffer str  reverse   toString        int count   0      int preValue   0      int lastspaceIndexVal   str lastIndexOf           int strLen   str length        for  int i   0  i  lt  strLen - 1  i              if  Character isWhitespace str charAt i                  if  i - preValue    1  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str substring i  strLen                   preValue   i                  count                  else if  i - preValue    2  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str charAt i - 2    str substring i  strLen                   preValue   i                  count                  else if  i - preValue    3  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str substring i  strLen                   preValue   i                  count                  else if  i - preValue    4  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str substring i  strLen                   preValue   i                  count                  else if  i - preValue    5  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str substring i - 2  i - 1    str charAt i - 3                            str charAt i - 3    str charAt i - 5                            str substring i  strLen                   preValue   i                  count                  else if  i - preValue    6  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str charAt i - 5                            str charAt i - 6    str substring i  strLen                   preValue   i                  count                  else if  i - preValue    7  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str charAt i - 5                            str charAt i - 6    str charAt i - 7                            str substring i  strLen                   preValue   i                  count                  else if  i - preValue    8  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str charAt i - 5                            str charAt i - 6    str charAt i - 7                            str charAt i - 8    str substring i  strLen                   preValue   i                  count                  else if  i - preValue    2  amp  amp  count    0                    str   str substring 0  preValue    str charAt i - 1                            str substring i  strLen                   preValue   i                else if  i - preValue    3  amp  amp  count    0                    str   str substring 0  preValue   1    str charAt i - 1                            str charAt i - 2    str substring i  strLen                   preValue   i                else if  i - preValue    4  amp  amp  count    0                    str   str substring 0  preValue   1    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str substring i  strLen                   preValue   i                else if  i - preValue    5  amp  amp  count    0                    str   str substring 0  preValue   1    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str substring i  strLen                   preValue   i                  count                  else if  i - preValue    6  amp  amp  count    0                    str   str substring 0  preValue   1    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str charAt i - 5                            str substring i  strLen                   preValue   i                  count                  else if  i - preValue    7  amp  amp  count    0                    str   str substring 0  preValue   1    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str charAt i - 5                            str charAt i - 6    str substring i  strLen                   preValue   i                  count                  else if  i - preValue    8  amp  amp  count    0                    str   str substring 0  preValue   1    str charAt i - 1                            str charAt i - 2    str charAt i - 3                            str charAt i - 4    str charAt i - 5                            str charAt i - 6    str charAt i - 7                            str substring i  strLen                   preValue   i                  count                              if  lastspaceIndexVal    preValue                    if  strLen - lastspaceIndexVal    2  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                       preValue   i                    else if  strLen - lastspaceIndexVal    3  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                                str charAt strLen - 2                       preValue   i                    else if  strLen - lastspaceIndexVal    4  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                                str charAt strLen - 2                                str charAt strLen - 3                       preValue   i                      count                      else if  strLen - lastspaceIndexVal    5  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                                str charAt strLen - 2                                str charAt strLen - 3                                str charAt strLen - 4                       preValue   i                    else if  strLen - lastspaceIndexVal    6  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                                str charAt strLen - 2                                str charAt strLen - 3                                str charAt strLen - 4                                str charAt strLen - 5                       preValue   i                      count                      else if  strLen - lastspaceIndexVal    7  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                                str charAt strLen - 2                                str charAt strLen - 3                                str charAt strLen - 4                                str charAt strLen - 5                                str charAt strLen - 6                       preValue   i                    else if  strLen - lastspaceIndexVal    8  amp  amp  count    0                        str   str substring 0  preValue   1                                str charAt strLen - 1                                str charAt strLen - 2                                str charAt strLen - 3                                str charAt strLen - 4                                str charAt strLen - 5                                str charAt strLen - 6                                str charAt strLen - 7                       preValue   i                                                      runtime gc           Calculate the used memory     long SecondaryUsageMemory   runtime totalMemory               - runtime freeMemory        System out println  Used memory in bytes      SecondaryUsageMemory       System out println str

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You can simply try like this take a string iterate over it using for loop till second last character of string and then simply reverse your loop like following    public class StringReverse       public static void main String ar             System out println reverseMe  iniana               static String reverseMe String s          String reverse              for int i   s length  -1  i gt  0  i--              resverse   reverse   s charAt i                   return reverse

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Here you go    public static void main  String   args        System out println reverserString  Akshay        private static String reverserString String src        char   sArr   src toCharArray        char   dArr   new char sArr length       for int i sArr length  i gt 0  i--            dArr sArr length-i    sArr i-1              return new String dArr

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Try this   public  class Test        public static void main String   args            String s    welcome          for  int i 0  j    s length   -1  i  lt   j  j--              char c s charAt j         System out print c

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String x    stack overflow   String reversed       for int i   x length  -1   i gt  0  i--       reversed   reversed  x charAt i     System out println  reversed string is      reversed

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It is very simple using while loop  public class Test   public static void main String   args        String name    subha chandra       int len   name length        while len  gt  0           len--          char c   name charAt len           System out print c      use String valueOf c  to convert char to String

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ReverseString java  public class ReverseString       public static void main String   args            String str    Ranga Reddy           String revStr   reverseStr str           System out println revStr                      Way1 - Recursive     public static String reverseStr String str            char arrStr     reverseString 0  str toCharArray             return new String arrStr              private static char   reverseString int charIndex  char   arr                 if  charIndex  gt  arr length -  charIndex 1               return arr                     int startIndex   charIndex          int endIndex   arr length -  charIndex 1            char temp   arr startIndex                   arr startIndex    arr endIndex           arr endIndex    temp                charIndex                   return reverseString charIndex    arr                 Way2     private static String strReverse String str            char ch     new char str length             for  int i   str length   - 1  j   0  i  gt   0  i--                ch j      str charAt i                     return new String ch

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import java util Scanner  public class StringReverse       public static void main String   args              Read user Data From Console         Scanner sc   new Scanner System in           System out println  Enter Your String               Take an String so that it can Store the string data          String s1   sc nextLine              split the string and keep in an array         String   s2   s1 split               String s3                  reverse  the string and placed in an String s3         for  int i   0  i  lt  s2 length  i                  for  int j  s2 i  length  -1 j gt  0 j--                    s3    s2 i  charAt j                  for             s3                    for          System out println  After Reverse    s3           main    StringReverse

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How about a simple traverse from the end of the string to the beg   void printRev String str     for int i str length  -1 i gt  0 i--    System out print str charAt i

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import java util    public class Restring    public static void main String   args      String input output    Scanner kbd new Scanner System in     System out println  Please Enter a String      input kbd nextLine      int n input length       char tmp   new char n     char nxt   new char n      tmp input toCharArray      int m 0    for int i n-1 i gt  0 i--            nxt m  tmp i         m           System out print  Reversed String is         for int i 0 i lt n i              System out print nxt i

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public class Match    void comp String s1  String s2        char   charArray1   s1 toCharArray        char   charArray2   s2 toCharArray         int length1   charArray1 length               int length2   charArray2 length             int flag   0       if  length1    length2            for  int i   0  i  lt   length1 - 1  i                  if  charArray1 i     charArray2 i                     System out println  index are matched           charArray1 i           in index-    i                  else                   flag   1                  System out println  index are not matched           charArray1 i           in index-    i                   System out println  index are not matched           charArray2 i           in index-    i                                                     else           System out println  Your string are not matched by length              if  flag    0            System out println  Your string  matched with other String          else           System out println  Your string are not matched            public static void main String   args        java util Scanner sc   new java util Scanner System in       System out println  Enter the 1st String         String s1   sc nextLine        System out println  Enter the 2nd string        String s2   sc nextLine        Match m   new Match        m comp s1  s2

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public String reverse String arg        String tmp   null      if  arg length      1                return arg             else                String lastChar   arg substring arg length  -1 arg length              String remainingString   arg substring 0  arg length   -1            tmp   lastChar   reverse remainingString           return tmp

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public class ReverseWithoutStringAPI    public static void main String   args           String st  hello            StringBuffer b new StringBuffer             for int i st length  -1 i gt  0 i--                b append st charAt i               System out println  reverse     b

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final String s    123456789   final char   word   s toCharArray    final int l   s length   - 2  final int ll   s length   - 1  for  int i   0  i  lt  l  i          char x   word i       word i    word ll - i       word ll - i    x    System out println s   System out println new String word        You can do it either recursively or iteratively  looping    Iteratively   static String reverseMe String s        StringBuilder sb   new StringBuilder        for  int i   s length   - 1  i  gt   0  --i          sb append s charAt i        return sb toString        Recursively   static String reverseMe String s        if  s length      0          return         return s charAt s length   - 1    reverseMe s substring 1          Integer i   new Integer 15   test i   System out println i   test i   System out println i    public static void test  Integer i        i    Integer i   10

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What is suprising is that most of the answers are wrong  When Unicode is used  Seems like no one understands that java uses UTF-16 under the hood for Text encoding   Here is my simple answer   static String reverseMe String s       StringBuilder sb   new StringBuilder        int count   s codePointCount 0 s length        for int i   count - 1  i  gt   0  --i       sb append Character toChars s codePointAt i         return sb toString

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Code will be as below       public class A         public static void main String args            String str  hello         for int i str length  -1 i gt  0 i--           String str1 str charAt i           system out print str1

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public class StringReverse        public static void main String   args            String s   args 0            for  int i  s length  -1  i  gt   0  i--                               System out print s charAt i                             Prints the reversed string of the input

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public class StringReverse       public static void main String ar             System out println reverseMe  SRINIVAS               static String reverseMe String s           StringBuffer sb new StringBuffer            for int i s length  -1 i gt  0 --i               sb append s charAt i                      return sb toString

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Code will be as below   public class RemoveString    public static void main String   args     Scanner scanner new Scanner System in    String s scanner next     String st      for int i s length  -1 i gt  0 i--    st st s charAt i        System out println st

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Well  printing itself would suggest a predefined function     Presumably  though  you could obtain the characters and concatenate them manually in reverse  i e  loop over it backwards   Of course  you could say concatenation is a predefined function    so maybe the char array itself  But again    why   Is the source allowed to contain  egaugnal detatneiro tcejbo si avaj   -p  Also - note that string reversal is actually pretty complex if you consider unicode combining characters  surrogate pairs  etc  You should note the caveat that most string reversal mechanisms will only deal with the more common cases  but may struggle with i18n

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this is the best solution for this  public class String rev   public static void main String   args        String str  Karan Rajput       int ln str length        for  int i   ln  i  gt  0  i--            System out print str charAt i-1

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It can be done this way also   char c   str toCharArray      int i c lenght-1  public void printReverseString char   c  int i          if i  -1  return         System out println c i           printReverseString c --i

[java] Printing reverse of any String without using any predefined function?

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