打印每个词后面的空格

Question

有没有简单有效的方法可以把一组单词合并在一起，中间用空格隔开，但前后不要空格呢？

我想应该可以在循环中合并的时候去掉最后的空格（比如用 sum += (term + " ") 这种方式），不过我不太喜欢这样做。

最好是用Java、Python或者Ruby来写代码。

Answer 1

这是我现有的一个工具类的代码。

文件路径：C:\java\home\src\krc\utilz\Arrayz.java

package krc.utilz;

/**
 * A bunch of static helper methods for arrays of String's.
 * @See also krc.utilz.IntArrays for arrays of int's.
 */
public abstract class Arrayz
{
  /**
   * Concetenates the values in the given array into a string, seperated by FS.
   * @param FS String - Field Seperator - Name borrowed from awk
   * @param Object[] a - array to be concatentated
   * @return a string representation of the given array.
   */
  public static String join(String FS, Object[] a) {
    if (a==null||a.length==0) return "";
    StringBuilder result = new StringBuilder(String.valueOf(a[0]));
    for(int i=1; i<a.length; i++) {
      result.append(FS);
      result.append(String.valueOf(a[i]));
    }
    return result.toString();
  }

  ....

}

谢谢，Keith。

---

补充说明

这里有一个简单粗暴的性能比较，使用java.util.Arrays作为基准。

请注意，热点成本是经过100次迭代后计算的，应该对这三种方法来说（大致上）是相同的……krc.utilz.RandomString和krc.utilz.Arrayz这两个工具类可以根据需要提供，随时问我就行。

package forums;

import java.util.Arrays;
import krc.utilz.Arrayz;
import krc.utilz.RandomString;

class ArrayToStringPerformanceTest
{
  private static final int NS2MS = 1000000; // 1 millisecond (1/10^3) = 1,000,000 nanoseconds (1/10^9)

  public static void main(String[] args) {
    try {
      String[] array = randomStrings(100*1000, 16);
      long start, stop;
      String result;

      final int TIMES = 100;
      long time1=0L, time2=0L, time3=0L;

      for (int i=0; i<TIMES; i++) {

        start = System.nanoTime();
        result = Arrays.toString(array);
        stop = System.nanoTime();
        //System.out.println("Arrays.toString  took "+(stop-start)+" ns");
        time1 += (stop-start);

        start = System.nanoTime();
        result = Arrayz.join(", ", array);
        stop = System.nanoTime();
        //System.out.println("Arrayz.join      took "+(stop-start)+" ns");
        time2 += (stop-start);

        start = System.nanoTime();
        result = arrayToString(array, ", ");
        stop = System.nanoTime();
        //System.out.println("arrayToString    took "+(stop-start)+" ns");
        time3 += (stop-start);

      }
      System.out.format("java.util.Arrays.toString  took "+(time1/TIMES/NS2MS)+" ms");
      System.out.format("krc.utilz.Arrayz.join      took "+(time2/TIMES/NS2MS)+" ms");
      System.out.format("arrayToString              took "+(time3/TIMES/NS2MS)+" ms");

    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  public static String arrayToString(String[] array, String spacer) {
    StringBuffer result = new StringBuffer();
    for ( int i=0; i<array.length; i++ ) {
      result.append( array[i] + ((i+1<array.length)?spacer:"") );
    }
    return result.toString();
  }

  private static String[] randomStrings(int howMany, int length) {
    RandomString random = new RandomString();
    String[] a = new String[howMany];
    for ( int i=0; i<howMany; i++) {
      a[i] = random.nextString(length);
    }
    return a;
  }

}

/*
C:\Java\home\src\forums>"C:\Program Files\Java\jdk1.6.0_12\bin\java.exe" -Xms512m -Xmx1536m -enableassertions -cp C:\Java\home\classes forums.ArrayToStringPerformanceTest

java.util.Arrays.toString  took 26 ms
krc.utilz.Arrayz.join      took 32 ms
arrayToString              took 59 ms
*/

另外，看看Doomspork的建议，以及我对此的评论。

谢谢，Keith。

Answer 2

是的，这正是join的用途。下面是Ruby语言的写法：

["word", "another", "word"].join(" ")

<flamebait> 你可以看到，Ruby把join这个方法放在了Array（数组）上，而不是String（字符串）上，这样更合理一些。</flamebait>

Answer 3

在Python中，使用join方法会非常简单：

values = ["this", "is", "your", "array"]
result = " ".join(values)