Java开发网 - 高手帮下忙

Topic: 高手帮下忙

1.高手帮下忙

Posted by: pnwqcomputer
Posted on: 2005-07-08 21:12

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Original subject : 高手帮下忙


import java.io.*;
public class ym{
public static void main(String args[]) throws IOException
{
   int num;
   String str1;
   BufferedReader buffer1;
   buffer1=new BufferedReader(new InputStreamReader(System.in));
   while(true)
   {
      try
      {
         System.out.print("请输入成绩:");
         str1=buffer1.readLine();
         if (str1.length()<1){System.out.println("你必须输入一个数值!");}
         else {break;}
      }
  
   catch(IOException e)
   {
      continue;
   }
}
num=Integer.parseInt(str1);
if(num>=60){System.out.println(num+"是及格成绩");}
else{System.out.println(num+"不是及格分数");}
}
}

在 int num;后加上int i=1;后把true改为i==1为什么就通不过编译呢？？？帮下忙，谢谢了！！！！！

2.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: szaba Posted on: 2005-07-08 21:40 同样不懂不过在我的平台里编译报错只是认为str1应该初始化只要把String str1；这一句改为 String str1 = "";就行了

3.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: pnwqcomputer Posted on: 2005-07-08 21:45 同样不懂不过在我的平台里编译报错只是认为str1应该初始化只要把String str1；这一句改为 String str1 = "";就行了原程序是在书上抄来的，在我的平台上没报错！晕！！越来越多难点了！！！

4.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: szaba Posted on: 2005-07-08 22:39 没报错怎么叫通不过编译呢？

5.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: why Posted on: 2005-07-09 00:19 pnwqcomputer wrote: 在 int num;后加上int i=1;后把true改为i==1为什么就通不过编译呢？？？ ARE you sure? 原程序是在书上抄来的，在我的平台上没报错！ String str1; 这一句未改時没报错? ARE you sure?!?! Please be responsible for the information you provided. Check carefuly, please!

6.Re:高手帮下忙 [Re: why]	Copy to clipboard
Posted by: szaba Posted on: 2005-07-09 06:59 老大我试过的的确是原来不报错后来改了就报错了

7.Re:高手帮下忙 [Re: szaba]	Copy to clipboard
Posted by: why Posted on: 2005-07-09 07:48 szaba wrote: 老大我试过的的确是原来不报错后来改了就报错了 Could you compile the two files and show us what are on your Command Prompt window (assuming you're using one)? Show us the two files as well - 原来的 and 后来改了的

8.Re:高手帮下忙 [Re: pnwqcomputer]

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Posted by: pnwqcomputer
Posted on: 2005-07-09 08:43

原程序是《精彩java 2程序设计》第169页的（没报错)


import java.io.*;
public class ym{
public static void main(String args[]) throws IOException
{
   int num;
   String str1;
   BufferedReader buffer1;
   buffer1=new BufferedReader(new InputStreamReader(System.in));
   while(true)
   {
      try
      {
         System.out.print("请输入成绩:");
         str1=buffer1.readLine();
         if (str1.length()<1){System.out.println("你必须输入一个数值!");}
         else {break;}
      }
  
   catch(IOException e)
   {
      continue;
   }
}
num=Integer.parseInt(str1);
if(num>=60){System.out.println(num+"是及格成绩");}
else{System.out.println(num+"不是及格分数");}
}
}

修改后的是


import java.io.*;
public class ym{
public static void main(String args[]) throws IOException
{
   int num;
   int i=1;
   String str1;
   BufferedReader buffer1;
   buffer1=new BufferedReader(new InputStreamReader(System.in));
   while(i==1)
   {
      try
      {
         System.out.print("请输入成绩:");
         str1=buffer1.readLine();
         if (str1.length()<1){System.out.println("你必须输入一个数值!");}
         else {break;}
      }
  
   catch(IOException e)
   {
      continue;
   }
}
num=Integer.parseInt(str1);
if(num>=60){System.out.println(num+"是及格成绩");}
else{System.out.println(num+"不是及格分数");}
}
}

改后就报错了；

再改为：


import java.io.*;
public class ym{
public static void main(String args[]) throws IOException
{
   int num;
   int i=1;
   String str1="";
   BufferedReader buffer1;
   buffer1=new BufferedReader(new InputStreamReader(System.in));
   while(i==1)
   {
      try
      {
         System.out.print("请输入成绩:");
         str1=buffer1.readLine();
         if (str1.length()<1){System.out.println("你必须输入一个数值!");}
         else {break;}
      }
  
   catch(IOException e)
   {
      continue;
   }
}
num=Integer.parseInt(str1);
if(num>=60){System.out.println(num+"是及格成绩");}
else{System.out.println(num+"不是及格分数");}
}
}

又没报错！！高手们阿！Tell me why?Thank you!

9.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: why Posted on: 2005-07-09 11:56 > 原程序是《精彩java 2程序设计》第169页的（没报错) while (true) { ... str1=buffer1.readLine(); // would be run at least once (or Exception caught), so str1 would be initialized > 修改后的是 > 改后就报错了； num=Integer.parseInt(str1); // uninitialized local variable > 再改为： corrected now.

10.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: pnwqcomputer Posted on: 2005-07-09 13:18 谢谢你！可是我还有点不明白 > 修改后不是还要执行 str1=buffer1.readLine(); 不也一样初试化了吗？ Aren't "while (true)" and "int i=1;while(i==1)" the same?

11.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: why Posted on: 2005-07-09 21:17 pnwqcomputer wrote: 谢谢你！可是我还有点不明白 > 修改后不是还要执行 str1=buffer1.readLine(); 不也一样初试化了吗？ Aren't "while (true)" and "int i=1;while(i==1)" the same? The compiler is not clever enough to know that i==1 is always true.

12.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: szaba Posted on: 2005-07-10 11:13 呵呵应该说 compiler is clever enough! 不知道我这样理解对不对？当while(ture)的时候虽然 str1定义时没有赋初值编译也能通过而不报错但是当while(i==1)的时候就会要求 str1定义时必须赋初值？请WHY老大继续指教！谢谢

13.Re:高手帮下忙 [Re: szaba]	Copy to clipboard
Posted by: why Posted on: 2005-07-10 12:10 szaba wrote: 呵呵应该说 compiler is clever enough! As you like... The compiler won't tell whether i is still 1 from lines 7 to 10 (of "修改后的是"), so it won't assume that str1 would be initialized at line 15. I'm already out of patience, so please don't ask me any further.

14.Re:高手帮下忙 [Re: pnwqcomputer]	Copy to clipboard
Posted by: szaba Posted on: 2005-07-10 17:58 了解 WHY老大不是版主自然没有答疑解惑的职责想想幼时也因反应迟钝（？）不得老师之喜道理是一样的以后兄弟不指名老大指教就是这样老大什么时候 out of patience了只要视若无睹当偶放P便是了