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  1.  
  2. import java.util.*;
  3. import java.lang.*;
  4. import java.io.*;
  5.  
  6. class Ideone {
  7.  
  8. 	private static class Log {
  9.  
  10. 	    public static void logLoopStats(String name, long elapsedNano, int charCount) {
  11. 	        float timePerChar = (float) elapsedNano / (float) charCount;
  12. 	        String part1 = String.format("%s: %,dns, character count: %,d. ", name, elapsedNano, charCount);
  13. 	        String part2 = String.format("Time per character is %.3fns.", timePerChar);
  14. 	        System.out.println(part1 + part2);
  15. 	    }
  16.  
  17. 	}
  18.  
  19. 	public static void main(String[] args) throws Exception {
  20.         List<String> list = new ArrayList<>();
  21.  
  22.         for (int j = 0; j < 1000000; j++) {
  23.             list.add("one");
  24.             list.add("two");
  25.             list.add("three");
  26.             list.add("four");
  27.             list.add("five");
  28.         }
  29.  
  30.         long startTime1 = System.nanoTime();
  31.         int count1 = loopWithI(list);
  32.         long elapsed1 = System.nanoTime() - startTime1;
  33.  
  34.         long startTime2 = System.nanoTime();
  35.         int count2 = loopWithISize(list);
  36.         long elapsed2 = System.nanoTime() - startTime2;
  37.  
  38.         long startTime3 = System.nanoTime();
  39.         int count3 = loopWithIterator(list);
  40.         long elapsed3 = System.nanoTime() - startTime3;
  41.  
  42.         long startTime4 = System.nanoTime();
  43.         int count4 = loopWithListIterator(list);
  44.         long elapsed4 = System.nanoTime() - startTime4;
  45.  
  46.         Log.logLoopStats("Loop with I, counting size", elapsed1, count1);
  47.         Log.logLoopStats("Loop with I, not counting size", elapsed2, count2);
  48.         Log.logLoopStats("Loop with iterator", elapsed3, count3);
  49.         Log.logLoopStats("Loop with list iterator", elapsed4, count4);
  50.     }
  51.  
  52.     private static int loopWithI(List<String> list) {
  53.         int i = 0;
  54.         int charCount = 0;
  55.         while (i < list.size()) {
  56.             charCount += list.get(i).length();
  57.             i++;
  58.         }
  59.         return charCount;
  60.     }
  61.  
  62.     private static int loopWithISize(List<String> list) {
  63.         int i = 0;
  64.         int charCount = 0;
  65.         int size = list.size();
  66.         while (i < size) {
  67.             charCount += list.get(i).length();
  68.             i++;
  69.         }
  70.         return charCount;
  71.     }
  72.  
  73.     private static int loopWithIterator(List<String> list) {
  74.         Iterator<String> iterator = list.iterator();
  75.         int charCount = 0;
  76.         while (iterator.hasNext()) {
  77.             charCount += iterator.next().length();
  78.         }
  79.         return charCount;
  80.     }
  81.  
  82.     private static int loopWithListIterator(List<String> list) {
  83.         ListIterator<String> listIterator = list.listIterator();
  84.         int charCount = 0;
  85.         while (listIterator.hasNext()) {
  86.             charCount += listIterator.next().length();
  87.         }
  88.         return charCount;
  89.     }
  90.  
  91. }
Success #stdin #stdout 0.7s 320512KB
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stdin
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Standard input is empty
stdout
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Loop with I, counting size: 95,307,356ns, character count: 19,000,000. Time per character is 5.016ns.
Loop with I, not counting size: 59,286,751ns, character count: 19,000,000. Time per character is 3.120ns.
Loop with iterator: 86,909,725ns, character count: 19,000,000. Time per character is 4.574ns.
Loop with list iterator: 85,995,007ns, character count: 19,000,000. Time per character is 4.526ns.
https://ideone.com/Td0jy8
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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