How do I concatenate two strings in Java

Question

I am trying to concatenate strings in Java   Why isn t this working   public class StackOverflowTest         public static void main String args              int theNumber   42          System out println  Your number is     theNumber

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String join  delimiter   stringA   stringB          As of Java 8 and later  we can use String join    Caveat  You must pass all String or CharSequence objects  So your int variable 42 does not work directly  One alternative is using an object rather than primitive  and then calling toString   Integer theNumber   42  String output        String                                                       String  class in Java 8 and later gained the new  join  method       join                                                       Static method on the  String  class                                                                   Delimiter           Your number is     theNumber toString                  A series of  String  or  CharSequence  objects that you want to join                                                                  Returns a  String  object of all the objects joined together separated by the delimiter      Dump to console    System out println  output       See this code run live at IdeOne com

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Out of the box you have 3 ways to inject the value of a variable into a String as you try to achieve   1  The simplest way  You can simply use the operator   between a String and any object or primitive type  it will automatically concatenate the String and    In case of an object  the value of String valueOf obj  corresponding to the String  null  if obj is null otherwise the value of obj toString    In case of a primitive type  the equivalent of String valueOf  lt primitive-type gt      Example with a non null object   Integer theNumber   42  System out println  Your number is     theNumber           Output   Your number is 42    Example with a null object   Integer theNumber   null  System out println  Your number is     theNumber           Output   Your number is null    Example with a primitive type   int theNumber   42  System out println  Your number is     theNumber           Output   Your number is 42    2  The explicit way and potentially the most efficient one  You can use StringBuilder  or StringBuffer the thread-safe outdated counterpart  to build your String using the append methods    Example   int theNumber   42  StringBuilder buffer   new StringBuilder        append  Your number is    append theNumber  append       System out println buffer toString        or simply System out println buffer    Output   Your number is 42    Behind the scene  this is actually how recent java compilers convert all the String concatenations done with the operator    the only difference with the previous way is that you have the full control    Indeed  the compilers will use the default constructor so the default capacity  16  as they have no idea what would be the final length of the String to build  which means that if the final length is greater than 16  the capacity will be necessarily extended which has price in term of performances    So if you know in advance that the size of your final String will be greater than 16  it will be much more efficient to use this approach to provide a better initial capacity  For instance  in our example we create a String whose length is greater than 16  so for better performances it should be rewritten as next   Example optimized    int theNumber   42  StringBuilder buffer   new StringBuilder 18       append  Your number is    append theNumber  append       System out println buffer    Output   Your number is 42    3  The most readable way  You can use the methods String format locale  format  args  or String format format  args  that both rely on a Formatter to build your String  This allows you to specify the format of your final String by using place holders that will be replaced by the value of the arguments    Example   int theNumber   42  System out println String format  Your number is  d    theNumber       Or if we need to print only we can use printf System out printf  Your number is still  d with printf  n   theNumber     Output   Your number is 42  Your number is still 42 with printf    The most interesting aspect with this approach is the fact that we have a clear idea of what will be the final String because it is much more easy to read so it is much more easy to maintain

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import com google common base Joiner   String delimiter       Joiner on delimiter  join Lists newArrayList  Your number is    47           This may be overkill to answer the op s question  but it is good to know about for more complex join operations  This stackoverflow question ranks highly in general google searches in this area  so good to know

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here is an example to read and concatenate 2 string without using 3rd variable   public class Demo       public static void main String args    throws Exception            InputStreamReader r new InputStreamReader System in                BufferedReader br   new BufferedReader r           System out println  enter your first string            String str1   br readLine            System out println  enter your second string            String str2   br readLine            System out println  concatenated string is     str1   str2

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not      But be careful with String concatenation  Here s a link introducing some thoughts from IBM DeveloperWorks

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In java concatenate symbol is      If you are trying to concatenate two or three strings while using jdbc then use this   String u   t1 getString    String v   t2 getString    String w   t3 getString    String X   u        v        w  st setString 1  X     Here    is used for space only

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The java 8 way   StringJoiner sj1   new StringJoiner        String joined   sj1 add  one   add  two   toString       one  two System out println joined     StringJoiner sj2   new StringJoiner                 String joined2   sj2 add  Jake   add  John   add  Carl   toString        Jake  John  Carl  System out println joined2

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There are two basic answers to this question     simple  Use the   operator  string concatenation    your number is    theNumber         as noted elsewhere   less simple   Use StringBuilder  or StringBuffer     StringBuilder value  value append  your number is    value append theNumber   value append        value toString      I recommend against stacking operations like this   new StringBuilder   append  I   append  like to write   append  confusing code      Edit  starting in java 5 the string concatenation operator is translated into StringBuilder calls by the compiler  Because of this  both methods above are equal      Note  Spaceisavaluablecommodity asthissentancedemonstrates   Caveat  Example 1 below generates multiple StringBuilder instances and is less efficient than example 2 below  Example 1  String Blam   one   two  Blam    three   four  Blam    five   six    Example 2  String Blam   one   two   three   four   five   six

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So from the able answer s you might have got the answer for why your snippet is not working  Now I ll add my suggestions on how to do it effectively  This article is a good place where the author speaks about different way to concatenate the string and also given the time comparison results between various results    Different ways by which Strings could be concatenated in Java   By using   operator  20       By using concat method in String class Using StringBuffer  By using StringBuilder   Method 1   This is a non-recommended way of doing  Why  When you use it with integers and characters you should be explicitly very conscious of transforming the integer to toString   before appending the string or else it would treat the characters to ASCI int s and would perform addition on the top    String temp        200    B      This is translated internally into   new StringBuilder   append       append  200   append  B   toString      Method 2   This is the inner concat method s implementation   x000D   x000D  public String concat String str    x000D      int olen   str length    x000D      if  olen    0    x000D          return this  x000D        x000D      if  coder      str coder      x000D          byte   val   this value  x000D          byte   oval   str value  x000D          int len   val length   oval length  x000D          byte   buf   Arrays copyOf val  len   x000D          System arraycopy oval  0  buf  val length  oval length   x000D          return new String buf  coder   x000D        x000D      int len   length    x000D      byte   buf   StringUTF16 newBytesFor len   olen   x000D      getBytes buf  0  UTF16   x000D      str getBytes buf  len  UTF16   x000D      return new String buf  UTF16   x000D    x000D   x000D   x000D    This creates a new buffer each time and copies the old content to the newly allocated buffer  So  this is would be too slow when you do it on more Strings   Method 3   This is thread safe and comparatively fast compared to  1  and  2   This uses StringBuilder internally and when it allocates new memory for the buffer  say it s current size is 10  it would increment it s 2 size   2  which is 22   So when the array becomes bigger and bigger this would really perform better as it need not allocate buffer size each and every time for every append call     x000D   x000D      private int newCapacity int minCapacity    x000D             overflow-conscious code x000D          int oldCapacity   value length  gt  gt  coder  x000D          int newCapacity    oldCapacity  lt  lt  1    2  x000D          if  newCapacity - minCapacity  lt  0    x000D              newCapacity   minCapacity  x000D            x000D          int SAFE BOUND   MAX ARRAY SIZE  gt  gt  coder  x000D          return  newCapacity  lt   0    SAFE BOUND - newCapacity  lt  0  x000D                hugeCapacity minCapacity  x000D                newCapacity  x000D        x000D   x000D      private int hugeCapacity int minCapacity    x000D          int SAFE BOUND   MAX ARRAY SIZE  gt  gt  coder  x000D          int UNSAFE BOUND   Integer MAX VALUE  gt  gt  coder  x000D          if  UNSAFE BOUND - minCapacity  lt  0       overflow x000D              throw new OutOfMemoryError    x000D            x000D          return  minCapacity  gt  SAFE BOUND  x000D                minCapacity   SAFE BOUND  x000D        x000D   x000D   x000D    Method 4  StringBuilder would be the fastest one for String concatenation since it s not thread safe  Unless you are very sure that your class which uses this is single ton I would highly recommend not to use this one   In short  use StringBuffer until you are not sure that your code could be used by multiple threads  If  you are damn sure  that your class is singleton then go ahead with StringBuilder for concatenation

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For exact concatenation operation of two string please use   file names   file names concat file names1     In your case use   instead of

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you can use stringbuffer  stringbuilder  and as everyone before me mentioned       I m not sure how fast     is  I think it is the fastest for shorter strings   but for longer I think builder and buffer are about equal  builder is slightly faster because it s not synchronized

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You must be a PHP programmer   Use a   sign   System out println  Your number is     theNumber

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Using     symbol u can concatenate strings   String a  I    String b  Love     String c  Java    System out println a b c

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In Java  the concatenation symbol is      not

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The concatenation operator in java is    not    Read this  including all subsections  before you start  Try to stop thinking the php way     To broaden your view on using strings in Java - the   operator for strings is actually transformed  by the compiler  into something similar to   new StringBuilder   append  firstString   append  secondString   toString

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You can concatenate Strings using the   operator   String a  hello    String b  world    System out println a b     Output   hello world   That s it

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There are multiple ways to do so  but Oracle and IBM say that using    is a bad practice  because essentially every time you concatenate String  you end up creating additional objects in memory  It will utilize extra space in JVM  and your program may be out of space  or slow down   Using StringBuilder or StringBuffer is best way to go with it  Please look at Nicolas Fillato s comment above for example related to StringBuffer   String first    I eat    String second    all the rats     System out println first second

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First method  You could use     sign for concatenating strings  but this always happens in print  Another way  The String class includes a method for concatenating two strings  string1 concat string2

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Use   for string concatenation    Your number is     theNumber

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This should work  public class StackOverflowTest         public static void main String args                  int theNumber   42          System out println  Your number is     theNumber

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You can concatenate Strings using the   operator   System out println  Your number is     theNumber           theNumber is implicitly converted to the String  42

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instead of

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For better performance use str1 concat str2  where str1 and str2 are string variables

[java] How do I concatenate two strings in Java?

`String.join( delimiter , stringA , stringB , … )`

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