2013/05/29面试

三个编程题：1.String的map转成二维数组。2.Integer的List排序。3.某个目录下文件类型总数。

1.

import java.util.Iterator;import java.util.LinkedHashMap;import java.util.Map;import java.util.Set;public class Map2Array {public static void main(String[] args) {//Map m =new HashMap();  //显示的是3,2,1          Map<String,String> m =new LinkedHashMap<String, String>();  //显示的是1,2,3          m.put("1","aaaa");          m.put("2","baaa");          m.put("3","caaa");                 String[][] s = map2Array(m);        if(s!=null)        for(String [] ss:s){        for(String sss:ss){        System.out.print(sss+" ");        }        System.out.println();        }       }static String[][] map2Array(Map map) {int length = map==null?0:map.size();if(length==0){return null;}String[][] result= new String[length][2];Set set = map.keySet();Iterator iterator = set.iterator();int i=0;while(iterator.hasNext()) {String key = (String) iterator.next();result[i][0]=key;result[i++][1] = (String) map.get(key);}return result;}}

2

import java.util.ArrayList;import java.util.Collections;import java.util.List;public class ListSort {public static void main(String[] args) {List<Integer> oldList = new ArrayList<Integer>();oldList.add(1);oldList.add(5);oldList.add(8);oldList.add(2);System.out.println("开始: ");for(int i:oldList) {System.out.print(i+"-");}Collections.sort(oldList);System.out.println("\n升序: ");for(int i:oldList) {System.out.print(i+"-");}Collections.reverse(oldList);System.out.println("\n降序：");for(int i:oldList) {System.out.print(i+"-");}System.out.println("\n最大：");System.out.print(Collections.max(oldList));System.out.println("\n最小：");System.out.print(Collections.min(oldList));}}

3.

import java.io.File;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Set;public class CountKindsFile {/** * @param args */public static void main(String[] args) {String filePath = "F:\\Test";String fileType = "";File rootDirectory = new File(filePath);File[] files = rootDirectory.listFiles();System.out.println("总共有 "+files.length+" 个文件.");Map<String,Integer> m = new HashMap<String, Integer>();for(File f:files){if(f.isDirectory()) {if(m.containsKey("folder")) {m.put("folder", m.get("folder")+1);} else {m.put("folder", 1);}} else {fileType = f.getName().substring(f.getName().lastIndexOf(".")+1);if(m.containsKey(fileType)) {m.put(fileType, m.get(fileType)+1);} else {m.put(fileType, 1);}}}System.out.println("总共有 "+m.size()+" 种文件.");Set set = m.keySet();Iterator iterator = set.iterator();while(iterator.hasNext()) {String key = (String) iterator.next();Integer value = m.get(key);System.out.println(key+"有"+value+"个");}}}

结果：

分割————————————————————————————————————————————————————————————————————

两个数据库题：

1.表中有A B C三列,用SQL语句实现：当A列大于B列时选择A列否则选择B列，当B列大于C列时选择B列否则选C.

2.查询出每门课都大于80分的学生姓名 

score表

name   subject score
张三     语文       81
张三     数学       75
李四     语文       76  特意改为85
李四     数学       90
王五     语文       81
王五     数学       100
王五     英语       90

1.

select case when A>B then case when A>C then A else C end else case when B>C then B else C end end as name from member

详细看  猛击

2.在网上查询大量资料后，看到的情况都是李四的语文为76，特意改为85，按照网上的解决方案为：

select distinct name from score where name not in(select distinct name from score where score<80)

得到的结果为：李四和王五。

从题目中得知张三和李四是没有英语成绩，再怎么也不会出现在最后的结果里。

故我所写的有点繁琐：

select namefrom(select name,max(case subject when '语文' then score end) as yuwen,max(case subject when '数学' then score end) as shuxue,max(case subject when '英语' then score end) as enfrom scoregroup by name) tempwhere yuwen>80 and shuxue>80 and en>80;

若有好的SQL尽情贴上。