String Comparison in Java

Question

What does  compare two strings lexicographically  mean

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Below Algo  compare two strings lexicographically    Input two strings string 1 and string 2  for  int i   0  i  lt  str1 length    amp  amp       i  lt  str2 length    i        Loop through each character of both  strings comparing them until one  of the string terminates    a  If unicode value of both the characters    is same then continue   b  If unicode value of character of    string 1 and unicode value of string 2   is different then return  str1 i -str2 i   if length of string 1 is less than string2  return str2 str1 length     else   return str1 str2 length        This method compares two strings lexicographically  public static int compareCustom String s1  String s2        for  int i   0  i  lt  s1 length    amp  amp  i lt  s2 length    i              if s1 charAt i     s2 charAt i                  System out println  Equal                continue                    else              return s1 charAt i  - s2 charAt i                          if s1 length   lt s2 length             return s2 length   - s1 length              else if s1 length   gt s2 length             return s1 length  -s2 length              else          return 0                if two String are equal it will return 0 otherwise return Negative or   positive value   Source   - Source

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The String compareTo     method performs lexicographical comparison  Lexicographically    alphebetically

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Java lexicographically order    Numbers -before-  Uppercase -before- Lowercase   Odd as this seems  it is true   I have had to write comparator chains to be able to change the default behavior  Play around with the following snippet with better examples of input strings to verify the order  you will need JSE 8    import java util ArrayList   public class HelloLambda    public static void main String   args        ArrayList lt String gt  names   new ArrayList lt  gt         names add  Kambiz        names add  kambiz        names add  k1ambiz        names add  1Bmbiza        names add  Samantha        names add  Jakey        names add  Lesley        names add  Hayley        names add  Benjamin        names add  Anthony         names stream            filter e - gt  e contains  a             sorted            forEach System out  println         Result  1Bmbiza Benjamin Hayley Jakey Kambiz Samantha k1ambiz kambiz  Please note this is answer is Locale specific  Please note that I am filtering for a name containing the lowercase letter a

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Leading from answers from  Bozho and  aioobe  lexicographic comparisons are similar to the ordering that one might find in a dictionary   The Java String class provides the  compareTo    method in order to lexicographically compare Strings  It is used like this  apple  compareTo   banana     The return of this method is an int which can be interpreted as follows    returns  lt  0 then the String calling the method is lexicographically first  comes first in a dictionary  returns    0 then the two strings are lexicographically equivalent returns   0 then the parameter passed to the compareTo method is lexicographically first    More specifically  the method provides the first non-zero difference in ASCII values   Thus  computer  compareTo   comparison   will return a value of  int   u  -  int   a   20   Since this is a positive result  the parameter   comparison   is lexicographically first   There is also a variant  compareToIgnoreCase    which will return 0 for  a  compareToIgnoreCase   A    for example

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The wording  comparison  is mildly misleading   You are not comparing for strict equality but for which string comes first in the dictionary  lexicon    This is the feature that allows collections of strings to be sortable   Note that this is very dependent on the active locale   For instance  here in Denmark we have a character      which used to be spelled as  aa  and is very distinct from two single a s  EDIT   If pronounced as          Hence Danish sorting rules treat two consequtive a s identically to an       which means that it goes after z   This also means that Danish dictionaries are sorted differently than English or Swedish ones

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If you check which string would come first in a lexicon  you ve done a lexicographical comparison of the strings   Some links    Wikipedia - String  computer science  Lexicographical ordering Note on comparisons  lexicographic comparison between strings   Stolen from the latter link      A string s precedes a string t in lexicographic order if         s is a prefix of t  or   if c and d are respectively the first character of s and t in which s and t differ  then c precedes d in character order          Note  For the characters that are alphabetical letters  the character order coincides with the alphabetical order  Digits precede letters  and uppercase letters precede lowercase ones       Example          house precedes household   Household precedes house   composer precedes computer   H2O precedes HOTEL

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Comparing sequencially the letters that have the same position against each other   more like how you order words in a dictionary

[java] String Comparison in Java

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