How can I check if a single character appears in a string

Question

In Java is there a way to check the condition    Does this single character appear at all in string x   without using a loop

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static String removeOccurences String a  String b        StringBuilder s2   new StringBuilder a        for int i 0 i lt b length   i             char ch   b charAt i             System out println ch    first index  a indexOf ch             int lastind   a lastIndexOf ch        for int k new String s2  indexOf ch  k  gt  0 k new String s2  indexOf ch                if s2 charAt k     ch                   s2 deleteCharAt k           System out println  val of s2                 s2 toString                                          System out println s1 toString          return  s1 toString

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To check if something does not exist in a string  you at least need to look at each character in a string   So even if you don t explicitly use a loop  it ll have the same efficiency   That being said  you can try using str contains    char

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If you need to check the same string often you can calculate the character occurrences up-front  This is an implementation that uses a bit array contained into a long array   public class FastCharacterInStringChecker implements Serializable   private static final long serialVersionUID   1L   private final long   l   new long 1024      65536   64   1024  public FastCharacterInStringChecker final String string        for  final char c  string toCharArray              final int index   c  gt  gt  6          final int value   c -  index  lt  lt  6           l index     1L  lt  lt  value           public boolean contains final char c        final int index   c  gt  gt  6     c   64     final int value   c -  index  lt  lt  6      c -  index   64      return  l index   amp   1L  lt  lt  value      0

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static String removeOccurences String a  String b        StringBuilder s2   new StringBuilder a        for int i 0 i lt b length   i             char ch   b charAt i             System out println ch    first index  a indexOf ch             int lastind   a lastIndexOf ch        for int k new String s2  indexOf ch  k  gt  0 k new String s2  indexOf ch                if s2 charAt k     ch                   s2 deleteCharAt k           System out println  val of s2                 s2 toString                                          System out println s1 toString          return  s1 toString

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To check if something does not exist in a string  you at least need to look at each character in a string   So even if you don t explicitly use a loop  it ll have the same efficiency   That being said  you can try using str contains    char

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If you see the source code of indexOf in JAVA  public int indexOf int ch  int fromIndex             final int max   value length           if  fromIndex  lt  0                 fromIndex   0             else if  fromIndex  gt   max                    Note  fromIndex might be near -1 gt  gt  gt 1               return -1                       if  ch  lt  Character MIN SUPPLEMENTARY CODE POINT                    handle most cases here  ch is a BMP code point or a                 negative value  invalid code point                final char   value   this value               for  int i   fromIndex  i  lt  max  i                       if  value i     ch                         return i                                                 return -1             else                return indexOfSupplementary ch  fromIndex                      you can see it uses a for loop for finding a character  Note that each indexOf you may use in your code  is equal to one loop  So  it is unavoidable to use loop for a single character  However  if you want to find a special string with more different forms  use useful libraries such as util regex  it deploys stronger algorithm to match a character or a  string pattern with Regular Expressions  For example to find an email in a string  String regex    quot             quot     Pattern pattern   Pattern compile regex   Matcher matcher   pattern matcher email    If you don t like to use regex  just use a loop and charAt and try to cover all cases in one loop  Be careful recursive methods has more overhead than loop  so it s not recommended

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you can use this code  It will check the char is present or not  If it is present then the return value is  gt   0 otherwise it s -1  Here I am printing alphabets that is not present in the input   import java util Scanner   public class Test    public static void letters         System out println  Enter input char        Scanner sc   new Scanner System in       String input   sc next        System out println  Output           for  char alphabet    A   alphabet  lt    Z   alphabet                  if input toUpperCase   indexOf alphabet   lt  0                   System out print alphabet                 public static void main String   args        letters             Ouput Example Enter input char nandu Output    B C E F G H I J K L M O P Q R S T V W X Y Z

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You won t be able to check if char appears at all in some string without atleast going over the string once using loop   recursion   the built-in methods like indexOf also use a loop    If the no  of times you look up if a char is in string x is more way more than the length of the string than I would recommend using a Set data structure as that would be more efficient than simply using indexOf  String s    abc       Build a set so we can check if character exists in constant time O 1  Set lt Character gt  set   new HashSet lt  gt     int len   s length    for int i   0  i  lt  len  i    set add s charAt i        Now we can check without the need of a loop    contains method of set doesn t use a loop unlike string s contains method set contains  a      true set contains  z      false   Using set you will be able to check if character exists in a string in constant time O 1  but you will also use additional memory   Space complexity will be O n

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You can use string indexOf  a     If the char a is present in string        it returns the the index of the first occurrence of the character in   the character sequence represented by this object  or -1 if the   character does not occur

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Yes  using the indexOf   method on the string class  See the API documentation for this method

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Is the below what you were looking for  int index   string indexOf character   return index    -1

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String contains   which checks if the string contains a specified sequence of char values String indexOf   which returns the index within the string of the first occurence of the specified character or substring  there are 4 variations of this method

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If you see the source code of indexOf in JAVA  public int indexOf int ch  int fromIndex             final int max   value length           if  fromIndex  lt  0                 fromIndex   0             else if  fromIndex  gt   max                    Note  fromIndex might be near -1 gt  gt  gt 1               return -1                       if  ch  lt  Character MIN SUPPLEMENTARY CODE POINT                    handle most cases here  ch is a BMP code point or a                 negative value  invalid code point                final char   value   this value               for  int i   fromIndex  i  lt  max  i                       if  value i     ch                         return i                                                 return -1             else                return indexOfSupplementary ch  fromIndex                      you can see it uses a for loop for finding a character  Note that each indexOf you may use in your code  is equal to one loop  So  it is unavoidable to use loop for a single character  However  if you want to find a special string with more different forms  use useful libraries such as util regex  it deploys stronger algorithm to match a character or a  string pattern with Regular Expressions  For example to find an email in a string  String regex    quot             quot     Pattern pattern   Pattern compile regex   Matcher matcher   pattern matcher email    If you don t like to use regex  just use a loop and charAt and try to cover all cases in one loop  Be careful recursive methods has more overhead than loop  so it s not recommended

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To check if something does not exist in a string  you at least need to look at each character in a string   So even if you don t explicitly use a loop  it ll have the same efficiency   That being said  you can try using str contains    char

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Is the below what you were looking for  int index   string indexOf character   return index    -1

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You can use string indexOf  a     If the char a is present in string        it returns the the index of the first occurrence of the character in   the character sequence represented by this object  or -1 if the   character does not occur

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I m not sure what the original poster is asking exactly  Since indexOf      and contains      both probably use loops internally  perhaps he s looking to see if this is possible at all without a loop  I can think of two ways off hand  one would of course be recurrsion   public boolean containsChar String s  char search        if  s length      0          return false      else         return s charAt 0     search    containsChar s substring 1   search       The other is far less elegant  but completeness             Works for strings of up to 5 characters     public boolean containsChar String s  char search        if  s length    gt  5  throw IllegalArgumentException         try           if  s charAt 0     search  return true          if  s charAt 1     search  return true          if  s charAt 2     search  return true          if  s charAt 3     search  return true          if  s charAt 4     search  return true        catch  IndexOutOfBoundsException e               this should never happen            return false            return false      The number of lines grow as you need to support longer and longer strings of course  But there are no loops recurrsions at all  You can even remove the length check if you re concerned that that length   uses a loop

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String temp    abcdefghi   if temp indexOf  b    -1       System out println  there is  b  in temp string      else      System out println  there is no  b  in temp string

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package com  public class  index        public static void main String   args            String s1  be proud to be an indian           char ch s1 charAt s1 indexOf  e             int count   0           for int i 0 i lt s1 length   i                  if s1 charAt i    e                    System out println  number of E     ch                   count                                    System out println  Total count of E     count

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String contains String  or String indexOf String  - suggested  quot abc quot  contains  quot Z quot       false - correct  quot zzzz quot  contains  quot Z quot       false - correct  quot Z quot  contains  quot Z quot       true - correct  quot and quot  contains  quot  quot       true - correct  quot and quot  contains  quot  quot       false - correct  quot and quot  indexOf  quot  quot       0 - correct  quot and quot  indexOf  quot  quot       -1 - correct  String indexOf int  and carefully considered String indexOf char  with char to int widening  quot and quot  indexOf  quot  quot  charAt 0       0 though incorrect usage has correct output due to portion of correct data  quot and quot  indexOf  quot  quot  charAt 0       0 -- incorrect usage and ambiguous result  quot and quot  indexOf  quot  quot  codePointAt 0       -1 -- correct usage and correct output  The discussions around character is ambiguous in Java world can the value of char or Character considered as single character  No  In the context of unicode characters  char or Character can sometimes be part of a single character and should not be treated as a complete single character logically  if not  what should be considered as single character  logically   Any system supporting character encodings for Unicode characters should consider unicode s codepoint as single character  So Java should do that very clear  amp  loud rather than exposing too much of internal implementation details to users  String class is bad at abstraction  though it requires confusingly good amount of understanding of its encapsulations to understand the abstraction  and hence an anti-pattern   How is it different from general char usage  char can be only be mapped to a character in Basic Multilingual Plane  Only codePoint - int can cover the complete range of Unicode characters  Why is this difference  char is internally treated as 16-bit unsigned value and could not represent all the unicode characters using UTF-16 internal representation using only 2-bytes  Sometimes  values in a 16-bit range have to be combined with another 16-bit value to correctly define character  Without getting too verbose  the usage of indexOf  charAt  length and such methods should be more explicit  Sincerely hoping Java will add new UnicodeString and UnicodeCharacter classes with clearly defined  abstractions  Reason to prefer contains and not indexOf int   Practically there are many code flows that treat a logical character as char in java  In Unicode context  char is not sufficient Though the indexOf takes in an int  char to int conversion masks this from the user and user might do something like str indexOf someotherstr charAt 0   unless the user is aware of the exact context  So  treating everything as CharSequence  aka String  is better      public static void main String   args            System out println  quot and quot  indexOf  quot  quot  charAt 0        0 though incorrect usage has correct output due to portion of correct data         System out println  quot and quot  indexOf  quot  quot  charAt 0        0 -- incorrect usage and ambiguous result         System out println  quot and quot  indexOf  quot  quot  codePointAt 0        -1 -- correct usage and correct output         System out println  quot and quot  contains  quot  quot        true - correct         System out println  quot and quot  contains  quot  quot        false - correct

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Yes  using the indexOf   method on the string class  See the API documentation for this method

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String temp    abcdefghi   if temp indexOf  b    -1       System out println  there is  b  in temp string      else      System out println  there is no  b  in temp string

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I m not sure what the original poster is asking exactly  Since indexOf      and contains      both probably use loops internally  perhaps he s looking to see if this is possible at all without a loop  I can think of two ways off hand  one would of course be recurrsion   public boolean containsChar String s  char search        if  s length      0          return false      else         return s charAt 0     search    containsChar s substring 1   search       The other is far less elegant  but completeness             Works for strings of up to 5 characters     public boolean containsChar String s  char search        if  s length    gt  5  throw IllegalArgumentException         try           if  s charAt 0     search  return true          if  s charAt 1     search  return true          if  s charAt 2     search  return true          if  s charAt 3     search  return true          if  s charAt 4     search  return true        catch  IndexOutOfBoundsException e               this should never happen            return false            return false      The number of lines grow as you need to support longer and longer strings of course  But there are no loops recurrsions at all  You can even remove the length check if you re concerned that that length   uses a loop

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Yes  using the indexOf   method on the string class  See the API documentation for this method

User · Answer

You can use string indexOf  a     If the char a is present in string        it returns the the index of the first occurrence of the character in   the character sequence represented by this object  or -1 if the   character does not occur

User · Answer

To check if something does not exist in a string  you at least need to look at each character in a string   So even if you don t explicitly use a loop  it ll have the same efficiency   That being said  you can try using str contains    char

User · Answer

You can use string indexOf  a     If the char a is present in string        it returns the the index of the first occurrence of the character in   the character sequence represented by this object  or -1 if the   character does not occur

User · Answer

I m not sure what the original poster is asking exactly  Since indexOf      and contains      both probably use loops internally  perhaps he s looking to see if this is possible at all without a loop  I can think of two ways off hand  one would of course be recurrsion   public boolean containsChar String s  char search        if  s length      0          return false      else         return s charAt 0     search    containsChar s substring 1   search       The other is far less elegant  but completeness             Works for strings of up to 5 characters     public boolean containsChar String s  char search        if  s length    gt  5  throw IllegalArgumentException         try           if  s charAt 0     search  return true          if  s charAt 1     search  return true          if  s charAt 2     search  return true          if  s charAt 3     search  return true          if  s charAt 4     search  return true        catch  IndexOutOfBoundsException e               this should never happen            return false            return false      The number of lines grow as you need to support longer and longer strings of course  But there are no loops recurrsions at all  You can even remove the length check if you re concerned that that length   uses a loop

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You can use 2 methods from the String class    String contains   which checks if the string contains a specified sequence of char values String indexOf   which returns the index within the string of the first occurence of the specified character or substring or returns -1 if the character is not found  there are 4 variations of this method    Method 1   String myString    foobar   if  myString contains  x            Do something      Method 2   String myString    foobar   if  myString indexOf  x    gt   0          Do something      Links by  Zach Scrivena

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You can use 2 methods from the String class    String contains   which checks if the string contains a specified sequence of char values String indexOf   which returns the index within the string of the first occurence of the specified character or substring or returns -1 if the character is not found  there are 4 variations of this method    Method 1   String myString    foobar   if  myString contains  x            Do something      Method 2   String myString    foobar   if  myString indexOf  x    gt   0          Do something      Links by  Zach Scrivena

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String contains   which checks if the string contains a specified sequence of char values String indexOf   which returns the index within the string of the first occurence of the specified character or substring  there are 4 variations of this method

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you can use this code  It will check the char is present or not  If it is present then the return value is  gt   0 otherwise it s -1  Here I am printing alphabets that is not present in the input   import java util Scanner   public class Test    public static void letters         System out println  Enter input char        Scanner sc   new Scanner System in       String input   sc next        System out println  Output           for  char alphabet    A   alphabet  lt    Z   alphabet                  if input toUpperCase   indexOf alphabet   lt  0                   System out print alphabet                 public static void main String   args        letters             Ouput Example Enter input char nandu Output    B C E F G H I J K L M O P Q R S T V W X Y Z

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Yes  using the indexOf   method on the string class  See the API documentation for this method

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String contains String  or String indexOf String  - suggested  quot abc quot  contains  quot Z quot       false - correct  quot zzzz quot  contains  quot Z quot       false - correct  quot Z quot  contains  quot Z quot       true - correct  quot and quot  contains  quot  quot       true - correct  quot and quot  contains  quot  quot       false - correct  quot and quot  indexOf  quot  quot       0 - correct  quot and quot  indexOf  quot  quot       -1 - correct  String indexOf int  and carefully considered String indexOf char  with char to int widening  quot and quot  indexOf  quot  quot  charAt 0       0 though incorrect usage has correct output due to portion of correct data  quot and quot  indexOf  quot  quot  charAt 0       0 -- incorrect usage and ambiguous result  quot and quot  indexOf  quot  quot  codePointAt 0       -1 -- correct usage and correct output  The discussions around character is ambiguous in Java world can the value of char or Character considered as single character  No  In the context of unicode characters  char or Character can sometimes be part of a single character and should not be treated as a complete single character logically  if not  what should be considered as single character  logically   Any system supporting character encodings for Unicode characters should consider unicode s codepoint as single character  So Java should do that very clear  amp  loud rather than exposing too much of internal implementation details to users  String class is bad at abstraction  though it requires confusingly good amount of understanding of its encapsulations to understand the abstraction  and hence an anti-pattern   How is it different from general char usage  char can be only be mapped to a character in Basic Multilingual Plane  Only codePoint - int can cover the complete range of Unicode characters  Why is this difference  char is internally treated as 16-bit unsigned value and could not represent all the unicode characters using UTF-16 internal representation using only 2-bytes  Sometimes  values in a 16-bit range have to be combined with another 16-bit value to correctly define character  Without getting too verbose  the usage of indexOf  charAt  length and such methods should be more explicit  Sincerely hoping Java will add new UnicodeString and UnicodeCharacter classes with clearly defined  abstractions  Reason to prefer contains and not indexOf int   Practically there are many code flows that treat a logical character as char in java  In Unicode context  char is not sufficient Though the indexOf takes in an int  char to int conversion masks this from the user and user might do something like str indexOf someotherstr charAt 0   unless the user is aware of the exact context  So  treating everything as CharSequence  aka String  is better      public static void main String   args            System out println  quot and quot  indexOf  quot  quot  charAt 0        0 though incorrect usage has correct output due to portion of correct data         System out println  quot and quot  indexOf  quot  quot  charAt 0        0 -- incorrect usage and ambiguous result         System out println  quot and quot  indexOf  quot  quot  codePointAt 0        -1 -- correct usage and correct output         System out println  quot and quot  contains  quot  quot        true - correct         System out println  quot and quot  contains  quot  quot        false - correct

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String contains   which checks if the string contains a specified sequence of char values String indexOf   which returns the index within the string of the first occurence of the specified character or substring  there are 4 variations of this method

User · Answer

package com  public class  index        public static void main String   args            String s1  be proud to be an indian           char ch s1 charAt s1 indexOf  e             int count   0           for int i 0 i lt s1 length   i                  if s1 charAt i    e                    System out println  number of E     ch                   count                                    System out println  Total count of E     count

User · Answer

You won t be able to check if char appears at all in some string without atleast going over the string once using loop   recursion   the built-in methods like indexOf also use a loop    If the no  of times you look up if a char is in string x is more way more than the length of the string than I would recommend using a Set data structure as that would be more efficient than simply using indexOf  String s    abc       Build a set so we can check if character exists in constant time O 1  Set lt Character gt  set   new HashSet lt  gt     int len   s length    for int i   0  i  lt  len  i    set add s charAt i        Now we can check without the need of a loop    contains method of set doesn t use a loop unlike string s contains method set contains  a      true set contains  z      false   Using set you will be able to check if character exists in a string in constant time O 1  but you will also use additional memory   Space complexity will be O n

User · Answer

If you need to check the same string often you can calculate the character occurrences up-front  This is an implementation that uses a bit array contained into a long array   public class FastCharacterInStringChecker implements Serializable   private static final long serialVersionUID   1L   private final long   l   new long 1024      65536   64   1024  public FastCharacterInStringChecker final String string        for  final char c  string toCharArray              final int index   c  gt  gt  6          final int value   c -  index  lt  lt  6           l index     1L  lt  lt  value           public boolean contains final char c        final int index   c  gt  gt  6     c   64     final int value   c -  index  lt  lt  6      c -  index   64      return  l index   amp   1L  lt  lt  value      0

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I m not sure what the original poster is asking exactly  Since indexOf      and contains      both probably use loops internally  perhaps he s looking to see if this is possible at all without a loop  I can think of two ways off hand  one would of course be recurrsion   public boolean containsChar String s  char search        if  s length      0          return false      else         return s charAt 0     search    containsChar s substring 1   search       The other is far less elegant  but completeness             Works for strings of up to 5 characters     public boolean containsChar String s  char search        if  s length    gt  5  throw IllegalArgumentException         try           if  s charAt 0     search  return true          if  s charAt 1     search  return true          if  s charAt 2     search  return true          if  s charAt 3     search  return true          if  s charAt 4     search  return true        catch  IndexOutOfBoundsException e               this should never happen            return false            return false      The number of lines grow as you need to support longer and longer strings of course  But there are no loops recurrsions at all  You can even remove the length check if you re concerned that that length   uses a loop

User · Answer

String contains   which checks if the string contains a specified sequence of char values String indexOf   which returns the index within the string of the first occurence of the specified character or substring  there are 4 variations of this method

[java] How can I check if a single character appears in a string?

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