解析Java程序设计答案

1、Java作业P201：5如何改进下面的程序以提高其执行性能？对你的改进作出解释，并写出新的程序。int i;URL url = new URL("bbb:/java.sunaaa/");URLConnection javaSite = url.openConnection();InputStream input = javaSite.getInputStream();InputStreamReader reader = new InputStreamReader(input);while (i = reader.read() != -1) System.out.print(

2、i);答: 使用缓冲流！在这里，可以增加两个缓冲流： 在InputStream 上增加一个BufferedInputStream ，在InputStreamReader 上增加一个BufferedReader。改变后的程序如下：int i;URL url = new URL("bbb:/java.sunaaa/");URLConnection javaSite = url.openConnection();InputStream input = javaSite.getInputStream();BufferedInputStream in = new BufferedIn

3、putStream(input);BufferedReader reader = new BufferedReader(new InputStreamReader(in);while (i = reader.read() != -1) System.out.print(i);6查阅API文档中有关DataInputStream和DataOutputStream的内容。并编写一个程序使用readInt()方法从输入文件中读入学生成绩，求出学生的总成绩和平均成绩输出到另一个文件中。假设输入文件中的内容格式如下：姓名 语文 数学 外语张三 89 92 95李四 77 81 74王五 87 80 75

4、答：public static String readInputByRow(String path,int num) File file=new File(path); try FileInputStream fis = new FileInputStream(file); InputStreamReader isr = new InputStreamReader(fis, "UTF-8"); BufferedReader reader = new BufferedReader(isr); String tempstring="" int line=1;

5、 while(tempstring=reader.readLine()!=null) if(line=num) break; line+; reader.close(); isr.close(); fis.close(); return tempstring; catch (IOException e) e.printStackTrace(); return null; 10.改正下面的程序使其能通过编译答：public class catvoid test(File named)RandomAccessFile BufferedReader input = null;String line

6、= null;try input = new RandomAccessFile(named, "r");while(line = input.readLine()!=null)System.out.println(line);return;catch(FileNotFoundException fnf)System.err.println("File: " + named + " not found.");

7、catch(Exception e)         System.err.println(e.toString();)finally         if (input != null)             try  

8、60;              input.close();             catch(IOException io)                

9、;     p173：5：下面的程序片段有什么错误？能否通过编译？trycatch(Exception e)catch(ArithemeticException a)答：不能通过编译，ArithemeticException cannot be resolved to a typeDuplicate parameter a6：阅读程序，写出程序的运行结果。class first_exception public static void main(String args) char c; int a,b=0; int array=new int7

10、; String s="Hello" try a=1/b; catch(ArithmeticException ae) System.out.println("Catch "+ae); try array8=0; catch(ArrayIndexOutOfBoundsException ai) System.out.println("Catch "+ai); try c=s.charAt(8); catch(StringIndexOutOfBoundsException se) System.out.println("Cat

11、ch "+se); 答：运行结果：Catch java.lang.ArithmeticException: / by zeroCatch java.lang.ArrayIndexOutOfBoundsException: 8Catch java.lang.StringIndexOutOfBoundsException: String index out of range: 89: 试编写一个程序读入英文的Zero到Nine，输出其对应的阿拉伯数字，要求能对错误的输入按异常情况进行处理。程序：public String nvl(String str,String newStr) ret

12、urn str = null | "".equalsIgnoreCase(str)?newStr:str; public void output(String numberStr) numberStr = nvl(numberStr,"wrongNumber"); if("one".equalsIgnoreCase(numberStr) System.out.println(1); return; if("two".equalsIgnoreCase(numberStr) System.out.println(2);

13、 return; if("three".equalsIgnoreCase(numberStr) System.out.println(3); return; if("four".equalsIgnoreCase(numberStr) System.out.println(4); return; if("five".equalsIgnoreCase(numberStr) System.out.println(5); return; if("six".equalsIgnoreCase(numberStr) System

14、.out.println(6); return; if("seven".equalsIgnoreCase(numberStr) System.out.println(7); return; if("eight".equalsIgnoreCase(numberStr) System.out.println(8); return; if("nine".equalsIgnoreCase(numberStr) System.out.println(9); return; try if(numberStr.equalsIgnoreCase(&q

15、uot;wrongNumber") int a = 1 / 0; catch(Exception e) System.out.println("错误的输入！"); 12：import java.io.*;import java.util.Scanner;public class num public static void main(String args) / TODO Auto-generated method stubchar data=new char12;int i,b;String number;Scanner sc=new Scanner(Syste

16、m.in);trynumber=sc.nextLine();data=number.toCharArray();catch(Exception e)System.out.print(e.toString();tryif(data0!='0')b=1/0;catch (ArithmeticException e) System.out.print("区号必须0开头"); tryfor(i=0;i<12;i+)if(i!=3&&i!=4)if(!('0'<=datai&&datai<='9

17、')b=1/0;catch (ArithmeticException e) System.out.print("其他数字不为数字"); tryif(data3='-')if(data4='0')b=1/0;else if(data4='-')if(data5='0')b=1/0;catch (ArithmeticException e) System.out.print("号开头不能0开头"); tryif(data3!='-'&&data4!='-')b=1/0;catch (ArithmeticException e) System.out.print("