一个把List<String>转化为以","隔开的字符串的方法

 import java.util.ArrayList;
 import java.util.List;
 /**
  * 集合操作
  * @author intrl
  * @date 2010-12-15
  * @version 1.0
  */
 public class Test {

     public static void main(String[] args) {
         List<String> list=new ArrayList<String>();
         list.add("aaa");
         list.add("bbb");
         list.add("ccc");
         System.out.println(listToString(list));//aaa,bbb,ccc
     }

     public static String listToString(List<String> stringList){
         if (stringList==null) {
             return null;
         }
         StringBuilder result=new StringBuilder();
         boolean flag=false;
         for (String string : stringList) {
             if (flag) {
                 result.append(",");
             }else {
                 flag=true;
             }
             result.append(string);
         }
         return result.toString();
     }
 }

方法二:

 这代码太垃圾了
 为什么不
 int length = arr.length ;
 StringBuffer buf = new StringBuffer("");
 if(length > 0){
     buf.append(arr[0]);
 }
 for(int i = 1 ; i < length ; i++){
    buf.append(',');
    buf.append(arr[i]);
 }

方法三:

apache common包下的StringUtils的join方法:

StringUtils.join(list, ",");

以下其源码:

 public static String join(Iterator iterator, String separator) {

         // handle null, zero and one elements before building a buffer
         if (iterator == null) {
             return null;
         }
         if (!iterator.hasNext()) {
             return EMPTY;
         }
         Object first = iterator.next();
         if (!iterator.hasNext()) {
             return ObjectUtils.toString(first);
         }

         // two or more elements
         StringBuffer buf = new StringBuffer(256); // Java default is 16, probably too small
         if (first != null) {
             buf.append(first);
         }

         while (iterator.hasNext()) {
             if (separator != null) {
                 buf.append(separator);
             }
             Object obj = iterator.next();
             if (obj != null) {
                 buf.append(obj);
             }
         }
         return buf.toString();
     }