What is the best way to get the first letter from a string in Java returned as a string of length 1

Question

Assume the following   String example         something   String firstLetter          Are there differences to be aware of with the following ways of assigning firstLetter that could impact performance  which would be best  and why   firstLetter   String valueOf example charAt 0    firstLetter   Character toString example charAt 0    firstLetter   example substring 0  1     The reason the first letter is being returned as a String is that this is being run in Hadoop  and a string is required to assign to a Text type  firstLetter will be output as a key from a map   method  for example   public class FirstLetterMapper extends Mapper lt LongWritable  Text  Text  IntWritable gt        String line   new String        Text firstLetter   new Text        IntWritable wordLength   new IntWritable          Override     public void map LongWritable key  Text value  Context context              throws IOException  InterruptedException            line   value toString             for  String word   line split    W                  if  word length    gt  0                        ---------------------------------------------                    firstLetter assignment                 firstLetter set String valueOf word charAt 0   toLowerCase                        ---------------------------------------------                  wordLength set word length                     context write firstLetter  wordLength

User · Answer

import java io    class Initials        public static void main String args    throws IOException           BufferedReader br   new BufferedReader new InputStreamReader System in            String s          char x          int l          System out print  Enter any sentence              s   br readLine            s         s    adding a space infront of the inputted sentence or a name         s   s toUpperCase      converting the sentence into Upper Case  Capital Letters          l   s length      finding the length of the sentence         System out print  Output                for  int i   0  i  lt  l  i                  x   s charAt i     taking out one character at a time from the sentence             if  x           if the character is a space  printing the next Character along with a fullstop                 System out print s charAt i   1

User · Answer

Long story short  it probably doesn t matter  Use whichever you think looks nicest   Longer answer  using Oracle s Java 7 JDK specifically  since this isn t defined at the JLS   String valueOf or Character toString work the same way  so use whichever you feel looks nicer  In fact  Character toString simply calls String valueOf  source    So the question is  should you use one of those or String substring  Here again it doesn t matter much  String substring uses the original string s char   and so allocates one object fewer than String valueOf  This also prevents the original string from being GC ed until the one-character string is available for GC  which can be a memory leak   but in your example  they ll both be available for GC after each iteration  so that doesn t matter  The allocation you save also doesn t matter -- a char 1  is cheap to allocate  and short-lived objects  as the one-char string will be  are cheap to GC  too   If you have a large enough data set that the three are even measurable  substring will probably give a slight edge  Like  really slight  But that  if    measurable  contains the real key to this answer  why don t you just try all three and measure which one is fastest

User · Answer

import org openjdk jmh annotations Benchmark  import org openjdk jmh annotations BenchmarkMode  import org openjdk jmh annotations Fork  import org openjdk jmh annotations Measurement  import org openjdk jmh annotations Mode  import org openjdk jmh annotations OutputTimeUnit  import org openjdk jmh annotations Scope  import org openjdk jmh annotations Setup  import org openjdk jmh annotations State  import org openjdk jmh annotations Warmup   import java util concurrent TimeUnit    State Scope Thread   BenchmarkMode Mode AverageTime   OutputTimeUnit TimeUnit NANOSECONDS   Warmup iterations   5  time   1   Fork value   1   Measurement iterations   5  time   1  public class StringFirstCharBenchmark        private String source        Setup     public void init             source    MALE               Benchmark     public String substring             return source substring 0  1               Benchmark     public String indexOf             return String valueOf source indexOf 0              Results    ----------------------------------------------------------------------    Benchmark                           Mode  Cnt   Score   Error  Units    ----------------------------------------------------------------------    StringFirstCharBenchmark indexOf    avgt    5  23 777   5 788  ns op     StringFirstCharBenchmark substring  avgt    5  11 305   1 411  ns op    ----------------------------------------------------------------------

User · Answer

Performance wise substring 0  1  is better as found by following       String example    something       String firstLetter             long l System nanoTime        firstLetter   String valueOf example charAt 0        System out println  String valueOf      System nanoTime  -l         l System nanoTime        firstLetter   Character toString example charAt 0        System out println  Character toString      System nanoTime  -l         l System nanoTime        firstLetter   example substring 0  1       System out println  substring      System nanoTime  -l      Output   String valueOf  38553 Character toString  30451 substring  8660

User · Answer

String whole    something   String first   whole substring 0  1   System out println first

[java] What is the best way to get the first letter from a string in Java, returned as a string of length 1?

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