StringUtils.join,原集合為空,結果不為空
阿新 • • 發佈:2018-12-20
import org.apache.commons.collections.CollectionUtils; import org.apache.commons.lang.StringUtils; import java.util.ArrayList; import java.util.List; /** * @Desc **/ public class Test8 { public static void main(String[] args) { List<String> list = new ArrayList<String>(); System.out.println(list == null);//false String s = StringUtils.join(list, ",");//一定要注意,此時字串s不為空,是""。吃了大虧! System.out.println(s == null);//false System.out.println(s.length());//0 s = CollectionUtils.isEmpty(list) ? null : StringUtils.join(list, ",");//先判斷原list是否為空 System.out.println(s == null);//true list.add("a"); s = StringUtils.join(list, ","); System.out.println(s);//a list.add("b"); list.add("c"); s = StringUtils.join(list, ","); System.out.println(s);//a,b,c } }