How many spaces will Java String trim remove

Question

In Java  I have a String like this         content          Will String trim   remove all spaces on these sides or just one space on each

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All of them      Returns    A copy of this string with leading and trailing white space removed  or this string if it has no leading or trailing white space              Quoted from Java 1 5 0 docs       But why didn t you just try it and see for yourself

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Example of Java trim   removing spaces   public class Test       public static void main String   args                String str     n t This is be trimmed  n n            String newStr   str trim          removes newlines  tabs and spaces           System out println  old       str           System out println  new       newStr             OUTPUT  old     This is a String    new   This is a String

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trim   will remove all leading and trailing blanks  But be aware  Your string isn t changed  trim   will return a new string instance instead

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If your String input is   String a       abc      System out println a     Yes  output will be   abc   But if your String input is   String b        This  is  a  test    System out println b     Output will be This  is  a  test So trim only removes spaces before your first character and after your last character in the string and ignores the inner spaces  This is a piece of my code that slightly optimizes the built in String trim method removing the inner spaces and removes spaces before and after your first and last character in the string  Hope it helps   public static String trim char    input       char    output   new char  input length       int j 0      int jj 0      if input 0                        while input jj                       jj                     for int i jj  i lt input length  i           if input i             i   input length-1   amp  amp  input input length-1                    output j  input i           j                  else if  input i 1                 output j               j                            char    m   new char  j       int a 0      for int i 0  i lt m length  i           m i  output a         a              return new String  m

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See API for String class      Returns a copy of the string  with leading and trailing whitespace omitted     Whitespace on both sides is removed   Note that trim   does not change the String instance  it will return a new object    String original      content      String withoutWhitespace   original trim         original still refers to    content        and withoutWhitespace refers to  content

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One very important thing is that a string made entirely of  white spaces  will return a empty string   if a string sSomething    xxxxx   where x stand for white spaces  sSomething trim   will return an empty string   if a string sSomething    xxAxx   where x stand for white spaces  sSomething trim   will return A   if sSomething   xxSomethingxxxxAndSomethingxElsexxx   sSomething trim   will return SomethingxxxxAndSomethingxElse  notice that the number of x between words is not altered   If you want a neat packeted string combine trim   with regex as shown in this post  How to remove duplicate white spaces in string using Java    Order is meaningless for the result but trim   first would be more efficient  Hope it helps

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Trim   works for both sides

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If you want to check what will do some method  you can use BeanShell  It is a scripting language designed to be as close to Java as possible  Generally speaking it is interpreted Java with some relaxations  Another option of this kind is Groovy language  Both these scripting languages provide convenient Read-Eval-Print loop know from interpreted languages  So you can run console and just type         content       trim      You ll see  content  as a result after pressing Enter  or Ctrl R in Groovy console

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When in doubt  write a unit test    Test public void trimRemoveAllBlanks        assertThat      content     trim    is  content         NB  of course the test  for JUnit   Hamcrest  doesn t fail

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String formattedStr unformattedStr  formattedStr formattedStr trim   replaceAll    s

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To keep only one instance for the String  you could use the following   str      Hello        or  str   str trim      Then the value of the str String  will be str    Hello

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From the source code  decompiled       public String trim           int i   this count      int j   0      int k   this offset      char   arrayOfChar   this value      while   j  lt  i   amp  amp   arrayOfChar  k   j    lt                 j      while   j  lt  i   amp  amp   arrayOfChar  k   i - 1    lt               --i      return    j  gt  0      i  lt  this count     substring j  i    this         The two while that you can see mean all the characters whose unicode is below the space character s  at beginning and end  are removed

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One thing to point out  though  is that String trim has a peculiar definition of  whitespace   It does not remove Unicode whitespace  but also removes ASCII control characters that you may not consider whitespace      This method may be used to trim whitespace from the beginning and end of a string  in fact  it trims all ASCII control characters as well     If possible  you may want to use Commons Lang s StringUtils strip    which also handles Unicode whitespace  and is null-safe  too

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From java docs String class source           Returns a copy of the string  with leading and trailing whitespace    omitted      lt p gt     If this  lt code gt String lt  code gt  object represents an empty character    sequence  or the first and last characters of character sequence    represented by this  lt code gt String lt  code gt  object both have codes    greater than  lt code gt   amp  92 u0020  lt  code gt   the space character   then a    reference to this  lt code gt String lt  code gt  object is returned      lt p gt     Otherwise  if there is no character with a code greater than     lt code gt   amp  92 u0020  lt  code gt  in the string  then a new     lt code gt String lt  code gt  object representing an empty string is created    and returned      lt p gt     Otherwise  let  lt i gt k lt  i gt  be the index of the first character in the    string whose code is greater than  lt code gt   amp  92 u0020  lt  code gt   and let     lt i gt m lt  i gt  be the index of the last character in the string whose code    is greater than  lt code gt   amp  92 u0020  lt  code gt   A new  lt code gt String lt  code gt     object is created  representing the substring of this string that    begins with the character at index  lt i gt k lt  i gt  and ends with the    character at index  lt i gt m lt  i gt -that is  the result of     lt code gt this substring  lt i gt k lt  i gt   amp nbsp  lt i gt m lt  i gt  1  lt  code gt       lt p gt     This method may be used to trim whitespace  as defined above  from    the beginning and end of a string         return  A copy of this string with leading and trailing white             space removed  or this string if it has no leading or             trailing white space      public String trim     int len   count  int st   0  int off   offset          avoid getfield opcode    char   val   value        avoid getfield opcode     while   st  lt  len   amp  amp   val off   st   lt               st      while   st  lt  len   amp  amp   val off   len - 1   lt               len--    return   st  gt  0      len  lt  count     substring st  len    this      Note that after getting start and length it calls the substring method of String class

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Javadoc for String has all the details  Removes white space  space  tabs  etc   from both end and returns a new string

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Based on the Java docs here  the  trim   replaces   u0020  which is commonly known as whitespace    But take note  the   u00A0   Unicode NO-BREAK SPACE  amp nbsp    is also seen as a whitespace  and  trim   will NOT remove this  This is especially common in HTML   To remove it  I use    tmpTrimStr   tmpTrimStr replaceAll    u00A0          An example of this problem was discussed here

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It will remove all spaces on both the sides

[java] How many spaces will Java String.trim() remove?

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