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charAt() and substring method in java

Anonymous User 2554 10 Oct 2014

I want to go through each character in a String and pass each character of the String as a String to another function.

String s = "abcdefg";
for (int i = 0; i < s.length(); i++)
{
      newFunction(s.substring(i, i + 1));
}

or

String s = "abcdefg";
for (int i = 0; i < s.length(); i++)
{
       newFunction(Character.toString(s.charAt(i)));
}

Ask by Anonymous User

Updated 10 Oct 2014

1 Answers

Anonymous User 10 Oct 2014

As usual: it doesn't matter but if you insist on spending time on micro-optimization or if you really like to optimize for your very special use case, try this:

import org.junit.Assert;
import org.junit.Test;
 
public class StringCharTest {
 
    //
Times:
    // 1.Initialization of "s" outside the loop
    // 2.Init of "s" inside the loop
    // 3.newFunction() actually checks the string length,
    // sothe function will not be optimized away by the hotstop compiler
 
    @Test
    // Fastest:237ms / 562ms / 2434ms
    public void testCacheStrings() throws Exception {
        // Cacheall possible Char strings
        String[] char2string = new String[Character.MAX_VALUE];
        for (char i = Character.MIN_VALUE; i < Character.MAX_VALUE; i++)
{
            char2string[i] =Character.toString(i);
        }
 
        for (int x = 0; x < 10000000; x++) {
            char[] s = "abcdefg".toCharArray();
            for (int i = 0; i < s.length; i++) {
                newFunction(char2string[s[i]]);
            }
        }
    }
 
    @Test    // Fast:1687ms / 1725ms / 3382ms
    public void testCharToString() throws Exception {
        for (int x = 0; x < 10000000; x++) {
            String s = "abcdefg";
            for (int i = 0; i < s.length(); i++) {
                //Fast: Creates new String objects, but does not copy an array
               
newFunction(Character.toString(s.charAt(i)));
            }
        }
    }
 
    @Test    // Very fast: 1331 ms/ 1414ms / 3190ms
    public void testSubstring() throws Exception {
        for (int x = 0; x < 10000000; x++) {
            String s = "abcdefg";
            for (int i = 0; i < s.length(); i++) {
                //The fastest! Reuses the internal char array
                newFunction(s.substring(i, i +1));
            }
        }
    }
 
    @Test
    //Slowest: 2525ms / 2961ms / 4703ms
    public void testNewString() throws Exception {
        char[] value = new char[1];
        for (int x = 0; x < 10000000; x++) {
            char[] s = "abcdefg".toCharArray();
            for (int i = 0; i < s.length; i++) {
                value[0] = s[i];
                //Slow! Copies the array
                newFunction(new String(value));
            }
        }
    }
 
    private void newFunction(String string) {
        // Do something with the one-character string
        Assert.assertEquals(1, string.length());
    }
 
}

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