“无法找到符号”尽管正确的变量名

Question

在下面的代码片段中，我真的不明白为什么编译器会发出 “找不到符号”错误消息。

public class LU62XnsCvr extends Object 
{  
    // these two variables (among many others) are declared here as "public" 
    static StringBuffer message_data = new StringBuffer(); 
    static File Mesg_File = new File("C:\\...\\Mesg_File.txt"); // path snipped 

    public static void SendMesg() // This "method" is "called" from various 
           // sections of the LU62XnsCvr program 
    {  
    if (mesgcount == 1) 
     { 
     // On First call Connect the LU62XC Message File 
     FileOutputStream MesgOut = new FileOutputStream(Mesg_File); 
     FileChannel MesgChnl = MesgOut.getChannel(); 
     ByteBuffer Mesg_Bufr = ByteBuffer.allocate(128); 
     } 

    // Send Message to the Message Log 
    String mesg_str = message_data.toString(); // convert buffer to a string 
    MesgWork = mesg_str.getBytes();   // Convert string to byte array 
    Mesg_Bufr.put(MesgWork, bufroffset, MGbuflen); // copy MesgWork to buffer 
    MesgChnl.write(Mesg_Bufr); // write message buffer out to the file channel 
    Mesg_Bufr.clear(); 
    message_data.append("    "); // set message_data to 16 blanks 

    for (ndx = 0; ndx < MGbuflen; ++ndx) 
    { 
     MesgWork[ndx] = 0x20; // clear MesgWork byte area using blank character 
    } 
    } // End of Send Message log write sub-routine 

上面看起来对我来说没问题;但我得到以下几点：

src\LU62XnsCvr.java:444: cannot find symbol 
symbol : variable Mesg_Bufr 
location: class APPC_LU62.java.LU62XnsCvr 
    Mesg_Bufr.put(MesgWork, bufroffset, MGbuflen); 
    ^
src\LU62XnsCvr.java:445: cannot find symbol 
symbol : variable Mesg_Bufr 
location: class APPC_LU62.java.LU62XnsCvr 
    MesgChnl.write(Mesg_Bufr); 
        ^
src\LU62XnsCvr.java:445: cannot find symbol 
symbol : variable MesgChnl 
location: class APPC_LU62.java.LU62XnsCvr 
    MesgChnl.write(Mesg_Bufr); 
    ^
src\LU62XnsCvr.java:446: cannot find symbol 
symbol : variable Mesg_Bufr 
location: class APPC_LU62.java.LU62XnsCvr 
    Mesg_Bufr.clear(); 
    ^

除非我失去了一些东西，似乎是Mesg_Bufr“拼写为”正确。 为什么编译器不能找到变量？

Answer 1

您在if块中声明Mesg_Bufr，因此它只在该块中可见。

if (mesgcount == 1) 
{ 
    //On First call Connect the LU62XC Message File 
    FileOutputStream MesgOut = new FileOutputStream(Mesg_File) ; 
    FileChannel MesgChnl = MesgOut.getChannel() ; 
    ByteBuffer Mesg_Bufr = ByteBuffer.allocate(128) ; 
} 

其他人也一样。我不知道你想做什么（和tbh我不在乎），但为了使其正确运行，您可能必须将所有代码放在if中，或者更好的情况下，如果返回mesg != 1。