java題（可以當作面試）

今天一個朋友給以一些他面試的題，（學校和企業合作的，他說有點水，）
具體的題目就不說了，貼代碼：

class A {  
    public String show(D obj){  
           return ("A and D");  
    }   
    public String show(A obj){  
           return ("A and A");  
    }   
}   
class B extends A{  
    public String test(){
        return "test";
    }
    public String show(B obj){  
           return ("B and B");  
    }  
    public String show(A obj){  
           return ("B and A");  
    }   
}  
class C extends B{}   
class D extends B{}
public class testMain {

    public static void main(String ar[]) {
        /*編碼轉換*/
        String str = "測試";
        try{
            byte[] bs = str.getBytes("utf-8");
            String str1 = new String(bs, "iso-8859-1");
            System.out.println(str1);

            String str2 = new String(bs, "gb2312");
            System.out.println(str2);

            String str3 = new String(bs, "utf-8");
            System.out.println(str3);


            byte[] bs2 = str.getBytes("iso-8859-1");

            String str5 = new String(bs, "gb2312");
            System.out.println(str5);
        } catch(Exception e) {}

        /*多態，不明白的同學多看看重寫的定義，B中有一個方法是重寫的，一個是自定義的 */
        /*A a1 = new A();  
        A a2 = new B();  
        B b = new B();  
        C c = new C();   
        D d = new D();   
        System.out.println(a1.show(b));    
        System.out.println(a1.show(c));   
        System.out.println(a1.show(d));    
        System.out.println(a2.show(b));    
        System.out.println(a2.show(c));     
        System.out.println(a2.show(d));     
        System.out.println(b.show(b));      
        System.out.println(b.show(c));      
        System.out.println(b.show(d));    
        b.show

        /*文件
         * */
        /*System.out.println(new File("aaaa").exists());
        System.out.println(new File("aaa"));
        String path="E:";
        File file = new File(path);
        System.out.println(file.isDirectory());
        System.out.println(file.exists());
        if(file.isDirectory()) {
            File[] filelist = file.listFiles();
            for(int i = 0; i<filelist.length; i++) {
                if(filelist[i].isDirectory())
                System.out.println(filelist[i].getName());
                if(filelist[i].isFile()) {
                    System.out.println("文件：" + filelist[i].getName());
                }
            }
        }

        /*數組和集合的區別
         * 看博客
         * http://www.cnblogs.com/summers/p/4094260.html
         * http://blog.csdn.net/liu1695347/article/details/4627292
         * */
        /*List l = new ArrayList<>();

        l.add("132");
        l.add(1);
        l.add(1.0);

        System.out.println(l.get(0) instanceof String);
        System.out.println(l.get(1) instanceof Integer);
        System.out.println(l);


        /*時間*/
        /*Date d = new Date();
        System.out.println(d);

        System.out.println(d.getTimezoneOffset());
        System.out.println(d.getTime());
        System.out.println(d.getDate());

        System.out.println(d.getYear());
        System.out.println(d.getMonth());
        System.out.println(d.getDay());
        System.out.println(d.getHours());
        System.out.println(d.getMinutes());
        System.out.println(d.getSeconds());

         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
         String dateNowStr = sdf.format(d);  
         System.out.println("轉換日期格式" + dateNowStr);  

         String str = "2012-1-13 17:26:33";    
         try {
             Date today = sdf.parse(str);  
             System.out.println("時間轉換成String" + today);
         } catch(Exception e) {}

        Calendar now = Calendar.getInstance();
        System.out.println();
        System.out.println("年: " + now.get(Calendar.YEAR));  
        System.out.println("月: " + (now.get(Calendar.MONTH)+1));     
        System.out.println("日: " + now.get(Calendar.DAY_OF_MONTH));     
        System.out.println("時: " + now.get(Calendar.HOUR_OF_DAY));      
        System.out.println("分: " + now.get(Calendar.MINUTE));     
        System.out.println("秒: " + now.get(Calendar.SECOND));      
        System.out.println("1970" + now.getTimeInMillis());     
        System.out.println(now.getTime()); 
        now.set(Calendar.DATE, 1);
        now.roll(Calendar.DATE, -1);
        int MaxDate=now.get(Calendar.DATE);
        System.out.println("本月的最後一天是:"+MaxDate);


        /*取小數點前兩位，四捨五入*/
        /*double m=7237.3589;

        DecimalFormat df = new DecimalFormat("#.00");
        System.out.println(df.format(m));

        System.out.println(String.format("%.2f", m));

        /*String轉換int double*/
        /*String str = "123";

        Integer i = Integer.parseInt(str);
        System.out.println(i);

        Double d = Double.parseDouble(str);
        System.out.println(d);*/

        /*字符串逆序*/
        //StringBuilder sb = new StringBuilder("abc");
        //System.out.println(sb.reverse());
    }
}

編碼轉換的時候，手賤了，改了一下.java的編碼格式，我以爲能變回來，結果eclipse讓我失望了，漢字又敲了一遍，不對的地方希望同志們指出。
今晚是寫不完了。有空更新…..基礎很重要，基礎很重要，基礎很重要，