如何清空输入缓冲区的数据?

Question

注释部分为问题所在.如何能让第2次循环有效.
输入数据如下:
0
y
结果出现NumberFormatException异常.怀疑是输入的y存在于输入缓冲区中,导致进入第2次循环不需要输入数据(y应该被读取了).
执行subscription = Integer.parseInt(str)-1;语句.当然就会出现NumberFormatException异常了.
不知道我的看法对没对,请问如何解决能过输入第2次数据的问题?(就是继续输入月份.)
[code=Java
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;public class MonthDemo {
private static String[] month;
private static int subscription;
public static void main(String[] args) {
month = new String[]{"January","February","March","April","May","June",
"July","August","September","October","November","December",};
boolean flag = true;
char c;
String str;
while(flag){
System.out.print("请输入月份的数字: ");
try{
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
str = br.readLine(); //第2次循环到这里不需要输入数据,怀疑是输入缓冲区没有清空,输入的非n字符被读取.
subscription = Integer.parseInt(str)-1;
try{
if(subscription<0 || subscription>11)
{
throw new MyException();
}
else
{
System.out.println((subscription+1)+"月的英文为:"+month[subscription]);
flag = false;
}
}
catch(MyException e)
{
System.out.println(e);
System.out.println("退出请输入N,不退出则输入任意字符");
try{
c = (char)System.in.read();
if(c =='n' || c=='N' )
{
flag = false;
}

}
catch(IOException ex){
ex.printStackTrace();
}
}
}
catch(IOException e)
{
System.out.println("读入数据时出错~！");
}
}
}
}class MyException extends Exception{
MyException(String str){
super(str);
}
MyException(){
super();
}
public String toString(){
return "您输入的月份不合法~!";
}
}
][/code]

Answer 1

不好意思代码没贴好...import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;public class MonthDemo {
private static String[] month;
private static int subscription;
public static void main(String[] args) {
month = new String[]{"January","February","March","April","May","June",
"July","August","September","October","November","December",};
boolean flag = true;
char c;
String str;
while(flag){
System.out.print("请输入月份的数字: ");
try{
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
str = br.readLine(); //第2次循环到这里不需要输入数据,怀疑是输入缓冲区没有清空,输入的非n字符被读取.
subscription = Integer.parseInt(str)-1;
try{
if(subscription<0 || subscription>11)
{
throw new MyException();
}
else
{
System.out.println((subscription+1)+"月的英文为:"+month[subscription]);
flag = false;
}
}
catch(MyException e)
{
System.out.println(e);
System.out.println("退出请输入N,不退出则输入任意字符");
try{
c = (char)System.in.read();
if(c =='n' || c=='N' )
{
flag = false;
}

}
catch(IOException ex){
ex.printStackTrace();
}
}
}
catch(IOException e)
{
System.out.println("读入数据时出错~！");
}
}
}
}class MyException extends Exception{
MyException(String str){
super(str);
}
MyException(){
super();
}
public String toString(){
return "您输入的月份不合法~!";
}
}

Answer 2

  首先呢,你出的问题并不是没有清空缓存的原因,而是逻辑问题,最明显的就是成功输出月份的英文后你把flag=false他自然就停止循环了
  第2，你在第一个try那里捕捉的是IOException，也就是说，如果你输入数字n不能被Integer.parseInt(n),NumberFormatException这个异常你就捕获
不到,可以改成Exception
  自己把逻辑再整理下，很简单就能改好

Answer 3

首先,如何成功输入后,不会进入第2次循环.因为已经退出了.所以与你说的没有一点关系.
第2.我现在不是要捕获NumberFormatException.
最后,还是感谢你的回帖.

Answer 4

楼主输入y后，执行subscription = Integer.parseInt(str)-1;后会抛出NumberFormatException异常，注意，抛出异常后，try下面的语句就不执行了，所以直接到catch语句那里，而你又没捕捉该异常，那么java运行时系统就捕捉并输出了
另外，流中的数据不会存在于缓冲区的，readLIne()已经读出了！

Answer 5

我先输入的是0,然后再输入的是y...不是一开始输入y.暂时先不考虑一开始就输入y的情形,不知道我说清楚没?

Answer 6

这是我修改后的代码，也不是很好，但能实现楼主效果，你可以再改一改！
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;public class MonthDemo {
    private static String[] month;
    private static int subscription;
    public static void main(String[] args) {
        month = new String[]{"January","February","March","April","May","June",
                "July","August","September","October","November","December",};
        boolean flag = true;
        char c;
        String str;
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
                
        while(flag){
            System.out.print("请输入月份的数字: ");
            try{                str = br.readLine();    //第2次循环到这里不需要输入数据,怀疑是输入缓冲区没有清空,输入的非n字符被读取.
                //subscription = Integer.parseInt(str)-1;
                subscription = Integer.decode(str).intValue();
                if(subscription<0 || subscription>11)
                 {
                     throw new MyException();
                  }
                 else
                 {
                            System.out.println((subscription+1)+"月的英文为:"+month[subscription]);
                            //flag = false;
                  }
                 }
                catch(MyException e)
                {
                    System.out.println(e);
                    System.out.println("退出请输入N,不退出则输入任意字符");
                    try{
                        c = (char)br.read();
                        if(c =='n' || c=='N' )
                        {
                            flag = false;
                        }
                        else{
                         br.readLine();
                        }
                                                
                    }
                    catch(IOException ex){
                        ex.printStackTrace();
                    }                    
                }
            catch(NumberFormatException nfe){
             try{
             throw new MyException();
             }catch(MyException e)
                {
                    System.out.println(e);
                    System.out.println("退出请输入N,不退出则输入任意字符");
                    try{
                        c = (char)br.read();
                        if(c =='n' || c=='N' )
                        {
                            flag = false;
                        }
                        else
                        {
                         br.readLine();
                        }
                        
                                                
                    }
                    catch(IOException ex){
                        ex.printStackTrace();
                    }                    
                }
               
            }
            catch(IOException e)
            {
                System.out.println("读入数据时出错~！");
            }
        }
    }
}class MyException extends Exception{
    MyException(String str){
        super(str);
    }
    MyException(){
        super();
    }
    public String toString(){
        return "您输入的月份不合法~!";
    }
}

Answer 7

两者没区别吧！你输入0后输出结果当时是正确的，只是输入y后，出现异常，而异常正是y在传进subscription = Integer.parseInt(str)-1后抛出的！
哦，我上面的subscription = Integer.decode(str).intValue();不对，也应减一，楼主还是采用subscription = Integer.parseInt(str)-1就行

Answer 8

恩,现在问题聚焦在了(char)System.in.read()与(char)br.read()上面.
为什么第1个就会出现异常,第2个就不会出现异常呢?
能解释下吗?

Answer 9

这个对了！
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;public class MonthDemo {
    private static String[] month;
    private static int subscription;
    public static void main(String[] args) {
        month = new String[]{"January","February","March","April","May","June",
                "July","August","September","October","November","December",};
        boolean flag = true;
        char c;
        String str;
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
                
        while(flag){
            System.out.print("请输入月份的数字: ");
            try{                str = br.readLine();    //第2次循环到这里不需要输入数据,怀疑是输入缓冲区没有清空,输入的非n字符被读取.
                //subscription = Integer.parseInt(str)-1;
                subscription = Integer.decode(str).intValue();
                if(subscription<=0 || subscription>=12)
                 {
                     throw new MyException();
                  }
                 else
                 {
                            System.out.println((subscription)+"月的英文为:"+month[subscription-1]);
                            //flag = false;
                  }
                 }
                catch(MyException e)
                {
                    System.out.println(e);
                    System.out.println("退出请输入N,不退出则输入任意字符");
                    try{
                        c = (char)br.read();
                        if(c =='n' || c=='N' )
                        {
                            flag = false;
                        }
                        else{
                         br.readLine();//读完缓冲区
                        }
                                                
                    }
                    catch(IOException ex){
                        ex.printStackTrace();
                    }                    
                }
            catch(NumberFormatException nfe){
             try{
             throw new MyException();
             }catch(MyException e)
                {
                    System.out.println(e);
                    System.out.println("退出请输入N,不退出则输入任意字符");
                    try{
                        c = (char)br.read();
                        if(c =='n' || c=='N' )
                        {
                            flag = false;
                        }
                        else
                        {
                         br.readLine();
                        }
                        
                                                
                    }
                    catch(IOException ex){
                        ex.printStackTrace();
                    }                    
                }
               
            }
            catch(IOException e)
            {
                System.out.println("读入数据时出错~！");
            }
        }
    }
}class MyException extends Exception{
    MyException(String str){
        super(str);
    }
    MyException(){
        super();
    }
    public String toString(){
        return "您输入的月份不合法~!";
    }
}

Answer 10

System.in()和C中的scanf()及C++中的cin>>差不多，最后还会把我们结束输入的回车当做一个字符！其实br.read()也一样，只是我加了条br.readLine(),认为的把流中的数据读出了！！
这是我的理解，仅供参考，呵呵！