如何在 Java 中最佳化字串建立

問題描述

如何最佳化字串建立？

解決方案

利用 String.intern() 方法，以下範例優化了字串建立。

public class StringOptimization {
   public static void main(String[] args) {
      String variables[] = new String[50000];	  
      for( int i = 0; i < 50000; i++) {
         variables[i] = "s"+i;
      }
      long startTime0 = System.currentTimeMillis();
      
      for(int i = 0; i < 50000; i++) {
         variables[i] = "hello";
      }
      long endTime0 = System.currentTimeMillis();
      System.out.println("Creation time" 
         + " of String literals : "+ (endTime0 - startTime0) 
         + " ms" );
      long startTime1 = System.currentTimeMillis();
      
      for(int i = 0; i < 50000; i++) {
         variables[i] = new String("hello");
      }
      long endTime1 = System.currentTimeMillis();
      System.out.println("Creation time of" 
         + " String objects with 'new' key word : " 
         + (endTime1 - startTime1)
         + " ms");
      long startTime2 = System.currentTimeMillis();
      
      for(int i = 0; i < 50000; i++) {
         variables[i] = new String("hello");
         variables[i] = variables[i].intern();		  
      }
      long endTime2 = System.currentTimeMillis();
      System.out.println("Creation time of" 
         + " String objects with intern(): " 
         + (endTime2 - startTime2)
         + " ms");
   }
}

結果

上面的程式碼範例會產生以下結果。結果可能有所不同。

Creation time of String literals : 0 ms
Creation time of String objects with 'new' key word : 31 ms
Creation time of String objects with intern(): 16 ms