how to convert Lower case letters to upper case letters and upper case letters to lower case letters

Question

Alternately display any text that is typed in the textbox          in either Capital or lowercase depending on the original        letter changed   For example   CoMpUtEr will convert to        cOmPuTeR and vice versa      Switch addActionListener new ActionListener                 public void actionPerformed ActionEvent e                String characters    SecondTextField getText       String to read the user input             int length   characters length       change the string characters to length           for int i   0  i  lt  length  i       to check the characters of string                                       char character   characters charAt i                          if Character isUpperCase character                                  SecondTextField setText      characters toLowerCase                                else  if Character isLowerCase character                                  SecondTextField setText      characters toUpperCase       problem is here  how can i track the character which i already change above  means lowerCase

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You don t have to track whether you ve already changed the character from upper to lower  Your code is already doing that since it s basically   1   for each character x  2       if x is uppercase  3           convert x to lowercase 4       else  5           if x is lowercase  6                convert x to uppercase    The fact that you have that else in there  on line 4  means that a character that was initially uppercase will never be checked in the second if statement  on line 5    Example  start with A  Because that s uppercase  it will be converted to lowercase on line 3 and then you ll go back up to line 1 for the next character   If you start with z  the if on line 2 will send you directly to line 5 where it will be converted to uppercase  Anything that s neither upper nor lowercase will fail both if statements and therefore remain untouched

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Here you are some other version   public class Palindrom    public static void main String   args        Scanner sc   new Scanner System in       System out println  Enter a word to check          String checkWord   sc nextLine        System out println isPalindrome checkWord        sc close        public static boolean isPalindrome String str                StringBuilder secondSB   new StringBuilder        StringBuilder sb   new StringBuilder        sb append str       for int i   0  i lt sb length   i             char c   sb charAt i           if Character isUpperCase c                sb setCharAt i  Character toLowerCase c                        secondSB append sb       return sb toString   equals secondSB reverse   toString

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If you look at characters a-z  you ll see that all of them have the 6th bit is set to 1  Where in A-Z 6th bit is not set   A   1000001    a   1100001 B   1000010    b   1100010 C   1000011    c   1100011 D   1000100    d   1100100          Z   1011010    z   1111010   So all we need to do is to iterate through each character from a given string and then do XOR    with 32  In this way  the 6th bit can swap   Look at the below code for simply changing the string case without using any if-else conditions   public final class ChangeStringCase       public static void main String   args            String str    Hello World           for  int i   0  i  lt  str length    i                  char ans    char  str charAt i    32               System out print ans      Final Output  hELLO wORLD                     Time Complexity  O N  where N   Length of the string   Space Complexity  O 1

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This is to convert a letter from upper case to lower case import java util Scanner      public class ChangeCase           public static void main String  args                 String input              Scanner sc  new Scanner System in                   System out println  Enter Letter from upper case                    input sc next                 String result              result  input toLowerCase                System out println result

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You can use StringUtils swapCase   from org apache commons

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public class Toggle   public static String toggle String s        char   ch   s toCharArray         for  int i   0  i  lt  s length    i              char charat   ch i           if  Character isUpperCase charat                 charat   Character toLowerCase charat             else             charat   Character toUpperCase charat           System out print charat             return s       public static void main String   args        toggle  DivYa

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This is a better approach without using any String function   public static String ReverseCases String str        StringBuilder sb   new StringBuilder        for  int i   0  i  lt  str length    i            char temp        if  str charAt i   gt    a   amp  amp  str charAt i   lt    z             temp    char  str charAt i  - 32                 else if  str charAt i   gt    A   amp  amp  str charAt i   lt    Z            temp    char  str charAt i    32                 else           temp   str charAt i                  sb append temp             return sb toString

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setText is changing the text content to exactly what you give it  not appending it   Convert the String from the field first  then apply it directly     String value    This Is A Test   StringBuilder sb   new StringBuilder value   for  int index   0  index  lt  sb length    index          char c   sb charAt index       if  Character isLowerCase c             sb setCharAt index  Character toUpperCase c          else           sb setCharAt index  Character toLowerCase c             SecondTextField setText sb toString

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StringBuilder b   new StringBuilder     Scanner s   new Scanner System in   String n   s nextLine     for int i   0  i  lt  n length    i          char c   n charAt i        if Character isLowerCase c     true            b append String valueOf c  toUpperCase               else           b append String valueOf c  toLowerCase              System out println b

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String str1 str2      Scanner S new Scanner System in       str1 S nextLine        System out println str1       str2 S nextLine        str1 str1 concat str2       System out println str1 toLowerCase

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import java util Scanner  class TestClass       public static void main String args    throws Exception           Scanner s   new Scanner System in           String str   s nextLine            char   ch   str toCharArray            for  int i   0  i  lt  ch length  i                  if  Character isUpperCase ch i                      ch i    Character toLowerCase ch i                  else                   ch i    Character toUpperCase ch i                                    System out println ch

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Methods description    toLowerCase    Returns a new string with all characters converted to lowercase    toUpperCase    Returns a new string with all characters converted to uppercase     For example    Welcome  toLowerCase   returns a new string  welcome   Welcome  toUpperCase   returns a new string  WELCOME

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public static void main String   args        Scanner scanner   new Scanner System in       String satr scanner nextLine        String newString           for  int i   0  i  lt  satr length    i              if  Character isUpperCase satr charAt i                  newString  Character toLowerCase satr charAt i             else newString    Character toUpperCase satr charAt i              System out println newString

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The problem is that you are trying to set the value of SecondTextField after checking every single character in the original string  You should do the conversion  on the side   one character at a time  and only then set the result into the SecondTextField   As you go through the original string  start composing the output from an empty string  Keep appending the character in the opposite case until you run out of characters  Once the output is ready  set it into SecondTextField   You can make an output a String  set it to an empty string     and append characters to it as you go  This will work  but that is an inefficient approach  A better approach would be using a StringBuilder class  which lets you change the string without throwing away the whole thing

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This is a better method  -  void main  throws IOException       System out println  Enter sentence        BufferedReader br   new BufferedReader new InputStreamReader System in        String str   br readLine        String sentence           for int i 0 i lt str length   i                  if Character isUpperCase str charAt i    true                        char ch2   char  str charAt i  32               sentence   sentence   ch2                    else if Character isLowerCase str charAt i    true                        char ch2   char  str charAt i -32               sentence   sentence   ch2                    else         sentence  sentence   str charAt i              System out println sentence

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String name    Vikash   String upperCase   name toUpperCase    String lowerCase   name toLowerCase

[java] how to convert Lower case letters to upper case letters & and upper case letters to lower case letters

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