class bl2
{
            public static void main(String [] args)
            {
                        int x=12;
                        {
                            if(x<3)
                            {
                                        System.out.println("x<3");
                                        System.out.println("ok");
                            }
                            else if(x>=3 && x<8)
                                        System.out.println("x>=3 && x<8");
                        }
              int y;            
                        /*if(x>0)
                                        y=x;
                        else
                                        y=-x;*/
                        y=x>0?x:-x;
                    
                        if(x==1)
                                    {
                                    if(y==1)
                                                {
                                                System.out.println("x==1,y==1");
                                                }
                                    else
                                            {
                                                System.out.println("x==1,y!=1");
                                         }
                                      }
                      else if(x>3)   
                                  {
                                  if(y==1)
                                    {
                                                System.out.println("x!=1,y==1");
                                    }
                                    else
                                    {
                                                System.out.println("x!=1,y!=1");
                                    }
                                    }
                        
                        x=1;
                        switch(x)
                        {
                                        case 1:
                                                        System.out.println("switch1");
                                                        break;
                                        case 2:
                                                        System.out.println("seitch2");
                                                        break;
                                        case 3:
                                        case 4:
                                                                        System.out.println("3,4");
                                                                        break;
                                        default:
                                                        System.out.println("other");
                        }
                        try
                        {      
                        x=System.in.read();
                          }
                          catch(Exception e){}
                        while(x!='q')
                        {
                                        System.out.println((char)x);
                                        x=System.in.read();  
                                             try
                                {      
                                x =System.in.read();
                                }
                                catch(Exception e){}
                                }     
            }
}

//编译时总是说 bl2.java:69: 未报告的异常 ；必须对其进行捕捉或声明以便抛出
                                                        x=System.in.read();
                                                                        ^

while(x!='q'){
    System.out.println((char)x);
    x=System.in.read();
    try{      
        x =System.in.read();
    }catch(IOException e){
        System.err.println("IOException detected : " + e.getMessage());
    }
}

应该是因为没对第三行的那句read()做错误捕捉。
其实想省事点，直接在方法声明中表明该方法会排除异常。

public static void main(String [] args) throws IOException{
    ... ... ... ...
}

这样方法体内的 try 就可以省了。

多谢   说详细些该怎样改呢？

[[it] 本帖最后由 wenxx10 于 2008-8-20 13:48 编辑 [/it]]

while(x!='q'){
    System.out.println((char)x);
    try{
        x=System.in.read();
    }catch(IOException e){}
    try{      
        x =System.in.read();
    }catch(IOException e){
        System.err.println("IOException detected : " + e.getMessage());
    }
}

或者把程序里面所有的try/catch去掉，但是在main声明处注明：

public static void main(String [] args) throws IOException{
    ... ... ... ...
}

但是说实话，我看不明白，你为啥要连续写两边read()。不知道是啥用意。

xx  我也不懂视频上只是讲循环没将这个

bl2.java:3: 找不到符号
符号： 类 IOException
位置： 类 bl2
            public static void main(String [] args) throws IOException
                                                           ^
1 错误

可能是因为没导入包，在程序第一行写入：

import *;